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Linux Time - 魅族内核团队
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<a class="tag" href="/tags/#xtime" title="xtime">xtime</a>
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<a class="tag" href="/tags/#boottime" title="boottime">boottime</a>
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<h1>Linux Time</h1>
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Posted by Peng Weilin on
2018-07-12
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<h2 id="1、Linux时钟框架"><a href="#1、Linux时钟框架" class="headerlink" title="1、Linux时钟框架"></a>1、Linux时钟框架</h2><p><img src="linux_time_profile.png" alt="image">[^DroidPhoneo]</p>
<p>上图是linux时钟框架一个经典的描述。本质上linux各种时钟架构和服务是基于硬件提供的两种timer而构建的。</p>
<p>1、定时Timer</p>
<ul>
<li>这类timer每个cpu都有一个独立的，称为local timer。这类timer的中断一般都是PPI（Private Peripheral Interrupt）类型，即每个cpu都有独立一份中断。 与PPI对应的是SPI（Shared Peripheral Interrupt，即多个cpu共享同一个中断。</li>
<li>这类timer一般是32bit宽度count，最重要的它会频繁的溢出并产生timer到期中断。</li>
<li>这类timer服务于tick timer(低精度)或者hrtimer(高精度)。</li>
<li>低精度模式，local timer工作在PERIODIC模式。即timer以tick时间(1/HZ)周期性的产生中断。在tick timer中处理任务调度tick、低精度timer、其他时间更新和统计profile。在这种模式下，所有利用时间的进行的运算，精度都是以tick(1/HZ)为单位的，精度较低。比如HZ=1000，那么tick=1ms。</li>
<li>高精度模式，local timer工作在ONESHOT模式。即系统可以支持hrtimer(high resolution)高精度timer，精度为local timer的计数clk达到ns级别。这种情况下把tick timer也转换成一种hrtimer。</li>
</ul>
<p>2、时间戳Timer</p>
<ul>
<li>这类timer一个系统多个cpu共享一个，称为global timer。</li>
<li>这类timer一般是32bit/64bit宽度count，一般不会溢出产生中断，系统实时的去读取count的值来计算当前的时间戳。</li>
<li>这类timer服务于clocksource/timekeeper。</li>
</ul>
<blockquote>
<p>本文的代码分析基于linux kernel 4.4.22，最好的学习方法还是”RTFSC”</p>
</blockquote>
<h3 id="1-1、Exynos-MCT-Multi-Core-Timer"><a href="#1-1、Exynos-MCT-Multi-Core-Timer" class="headerlink" title="1.1、Exynos MCT(Multi-Core Timer)"></a>1.1、Exynos MCT(Multi-Core Timer)</h3><p>我们以samsung exynos架构为例来说明linux对timer的使用。</p>
<p><img src="exynos_timer.png" alt="image"></p>
<p>从上图可以看到，exynos有1个64bit global timer用来做时间戳timer，有8个31bit localtimer用来做定时timer，每个cpu拥有一个localtimer。</p>
<p><img src="exynos_mct_initflow.png" alt="image"></p>
<p>上图是exynos driver的初始化流程，mct_init_dt()中包含了主要的初始化流程：</p>
<figure class="highlight scss"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">static void __init <span class="built_in">mct_init_dt</span>(struct device_node *np, unsigned int int_type)</span><br><span class="line">{</span><br><span class="line"> <span class="built_in">exynos4_timer_resources</span>(np, of_iomap(np, <span class="number">0</span>)); <span class="comment">//(1)初始化localtimer，并将其注册成clockevent</span></span><br><span class="line"> <span class="built_in">exynos4_clocksource_init</span>(); <span class="comment">//(2)初始化globaltimer，并将其注册成clocksource</span></span><br><span class="line"> <span class="built_in">exynos4_clockevent_init</span>(); <span class="comment">//(3)将globaltimer的comparator 0注册成一个clockevent，一般不会使用</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>后面结合clocksource和clockevent的子系统的解析，再来详细描述exynos系统的具体实现。</p>
<h2 id="2、clocksource-timekeeper"><a href="#2、clocksource-timekeeper" class="headerlink" title="2、clocksource & timekeeper"></a>2、clocksource & timekeeper</h2><p><img src="clocksource_timekeeper.png" alt="image"></p>
<p>上图描述的是clocksource和timekeeper的关系：</p>
<ul>
<li>一个global timer对应注册一个clocksource。</li>
<li>一个系统中可以有多个clocksource，timekeeper选择精度最高的那个来使用。</li>
<li>用户使用timekeeper提供的接口来获取系统的时间戳。</li>
<li>为了避免无人主动获取时间clocksource定时器的溢出，timekeeper需要定期的去获取clocksource的值来更新系统时间，一般是在tick处理中更新。</li>
</ul>
<h3 id="2-1、clocksource"><a href="#2-1、clocksource" class="headerlink" title="2.1、clocksource"></a>2.1、clocksource</h3><p>下面来看一看clocksource的定义：</p>
<figure class="highlight jboss-cli"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line">static struct clocksource mct_frc = {</span><br><span class="line"> <span class="string">.name</span> = <span class="string">"mct-frc"</span>,</span><br><span class="line"> /* <span class="params">(1)</span> <span class="string">.rating</span> = 精度，数值越大越好，</span><br><span class="line"> select_best会选择精度最大的clocksource给timekeeper使用 */</span><br><span class="line"> <span class="string">.rating</span> = 400, </span><br><span class="line"> /* <span class="params">(2)</span> <span class="string">.read</span> = 读取clocksource的timer当前计数 */</span><br><span class="line"> <span class="string">.read</span> = exynos4_frc_read,</span><br><span class="line"> /* <span class="params">(3)</span> <span class="string">.mask</span> = timer的位宽 */</span><br><span class="line"> <span class="string">.mask</span> = CLOCKSOURCE_MASK<span class="params">(32)</span>,</span><br><span class="line"> <span class="string">.flags</span> = CLOCK_SOURCE_IS_CONTINUOUS,</span><br><span class="line"> <span class="string">.resume</span> = exynos4_frc_resume,</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<p>看一下clocksource的注册过程：</p>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br></pre></td><td class="code"><pre><span class="line">static void __init exynos4_clocksource_init(void)</span><br><span class="line">{</span><br><span class="line"> <span class="comment">// 启动global timer</span></span><br><span class="line"> exynos4_mct_frc_start();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 注册timer_delay</span></span><br><span class="line"> exynos4_delay_timer.read_current_timer = &exynos4_read_current_timer;</span><br><span class="line"> exynos4_delay_timer.freq = clk_rate;</span><br><span class="line"> register_current_timer_delay(&exynos4_delay_timer);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (1) 注册clocksource</span></span><br><span class="line"> <span class="keyword">if</span> (clocksource_register_hz(&mct_frc, clk_rate))</span><br><span class="line"> panic(<span class="string">"%s: can't register clocksource\n"</span>, mct_frc.<span class="keyword">name</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 注册sched_clock</span></span><br><span class="line"> sched_clock_register(exynos4_read_sched_clock, <span class="number">32</span>, clk_rate);</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">static inline int clocksource_register_hz(struct clocksource *cs, u32 hz)</span><br><span class="line">{</span><br><span class="line"> return __clocksource_register_scale(cs, <span class="number">1</span>, hz);</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line">int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)</span><br><span class="line">{</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Initialize mult/shift and max_idle_ns */</span></span><br><span class="line"> <span class="comment">/* (1.1) 根据timer的频率freq，计算cs->mult、cs->shift</span></span><br><span class="line"><span class="comment"> 这两个字段是用来把timer的计数转换成实际时间单位ns</span></span><br><span class="line"><span class="comment"> ns = (count * cs->mult) >> cs->shift */</span></span><br><span class="line"> __clocksource_update_freq_scale(cs, scale, freq);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Add clocksource to the clocksource list */</span></span><br><span class="line"> mutex_lock(&clocksource_mutex);</span><br><span class="line"> <span class="comment">/* (1.2) 将新的clocksource加入全局链表 */</span></span><br><span class="line"> clocksource_enqueue(cs);</span><br><span class="line"> clocksource_enqueue_watchdog(cs);</span><br><span class="line"> <span class="comment">/* (1.3) 从全局链表中重新选择一个best</span></span><br><span class="line"><span class="comment"> clocksource给timekeeper使用 */</span></span><br><span class="line"> clocksource_select();</span><br><span class="line"> clocksource_select_watchdog(<span class="literal">false</span>);</span><br><span class="line"> mutex_unlock(&clocksource_mutex);</span><br><span class="line"> return <span class="number">0</span>;</span><br><span class="line">}</span><br><span class="line">|||→</span><br><span class="line">void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)</span><br><span class="line">{</span><br><span class="line"> u64 sec;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Default clocksources are *special* and self-define their mult/shift.</span></span><br><span class="line"><span class="comment"> * But, you're not special, so you should specify a freq value.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (freq) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Calc the maximum number of seconds which we can run before</span></span><br><span class="line"><span class="comment"> * wrapping around. For clocksources which have a mask > 32-bit</span></span><br><span class="line"><span class="comment"> * we need to limit the max sleep time to have a good</span></span><br><span class="line"><span class="comment"> * conversion precision. 10 minutes is still a reasonable</span></span><br><span class="line"><span class="comment"> * amount. That results in a shift value of 24 for a</span></span><br><span class="line"><span class="comment"> * clocksource with mask >= 40-bit and f >= 4GHz. That maps to</span></span><br><span class="line"><span class="comment"> * ~ 0.06ppm granularity for NTP.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (1.1.1) 计算timer计数器到溢出，</span></span><br><span class="line"><span class="comment"> 最大能计数多少秒 = sec */</span></span><br><span class="line"> <span class="function"><span class="title">sec</span> = cs-></span>mask;</span><br><span class="line"> do_div(sec, freq);</span><br><span class="line"> do_div(sec, scale);</span><br><span class="line"> <span class="keyword">if</span> (!sec)</span><br><span class="line"> sec = <span class="number">1</span>;</span><br><span class="line"> <span class="function"><span class="title">else</span> <span class="keyword">if</span> (sec > 600 && cs-></span>mask > UINT_MAX)</span><br><span class="line"> sec = <span class="number">600</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.1.2) 根据1s内的频率数freq，和1s内的ns数NSEC_PER_SEC</span></span><br><span class="line"><span class="comment"> 计算freq和ns之间的转换公式：</span></span><br><span class="line"><span class="comment"> ns = (freq * cs->mult) >> cs->shift </span></span><br><span class="line"><span class="comment"> 目的是把mult和shift算到最大值，最大可能的保留精度 */</span></span><br><span class="line"> <span class="function"><span class="title">clocks_calc_mult_shift</span>(&cs-></span><span class="function"><span class="title">mult</span>, &cs-></span>shift, freq,</span><br><span class="line"> NSEC_PER_SEC / scale, sec * scale);</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Ensure clocksources that have large 'mult' values don't overflow</span></span><br><span class="line"><span class="comment"> * when adjusted.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span>maxadj = clocksource_max_adjustment(cs);</span><br><span class="line"> <span class="function"><span class="title">while</span> (freq && ((cs-></span><span class="function"><span class="title">mult</span> + cs-></span><span class="function"><span class="title">maxadj</span> < cs-></span>mult)</span><br><span class="line"> || (<span class="function"><span class="title">cs</span>-></span><span class="function"><span class="title">mult</span> - cs-></span><span class="function"><span class="title">maxadj</span> > cs-></span>mult))) {</span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span>mult >>= <span class="number">1</span>;</span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span>shift--;</span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span>maxadj = clocksource_max_adjustment(cs);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Only warn for *special* clocksources that self-define</span></span><br><span class="line"><span class="comment"> * their mult/shift values and don't specify a freq.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> WARN_ONCE(<span class="function"><span class="title">cs</span>-></span><span class="function"><span class="title">mult</span> + cs-></span><span class="function"><span class="title">maxadj</span> < cs-></span>mult,</span><br><span class="line"> <span class="string">"timekeeping: Clocksource %s might overflow on 11%% adjustment\n"</span>,</span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span><span class="keyword">name</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.1.3) 根据mult和shift的值，计算最大能进入idle的时间max_idle_ns</span></span><br><span class="line"><span class="comment"> 才能保证idle时timer不会溢出*/</span></span><br><span class="line"> clocksource_update_max_deferment(cs);</span><br><span class="line"></span><br><span class="line"> pr_info(<span class="string">"%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n"</span>,</span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span><span class="function"><span class="title">name</span>, cs-></span><span class="function"><span class="title">mask</span>, cs-></span><span class="function"><span class="title">max_cycles</span>, cs-></span>max_idle_ns);</span><br><span class="line">}</span><br><span class="line">|||→</span><br><span class="line">static void clocksource_select(void)</span><br><span class="line">{</span><br><span class="line"> __clocksource_select(<span class="literal">false</span>);</span><br><span class="line">}</span><br><span class="line">static void __clocksource_select(bool skipcur)</span><br><span class="line">{</span><br><span class="line"> bool oneshot = tick_oneshot_mode_active();</span><br><span class="line"> struct clocksource *best, *cs;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Find the best suitable clocksource */</span></span><br><span class="line"> <span class="comment">/* (1.3.1) 选择best clocksource */</span></span><br><span class="line"> best = clocksource_find_best(oneshot, skipcur);</span><br><span class="line"> <span class="keyword">if</span> (!best)</span><br><span class="line"> return;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Check for the override clocksource. */</span></span><br><span class="line"> list_for_each_entry(cs, &clocksource_list, list) {</span><br><span class="line"> <span class="keyword">if</span> (skipcur && cs == curr_clocksource)</span><br><span class="line"> continue;</span><br><span class="line"> <span class="function"><span class="title">if</span> (strcmp(cs-></span><span class="keyword">name</span>, override_name) != <span class="number">0</span>)</span><br><span class="line"> continue;</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Check to make sure we don't switch to a non-highres</span></span><br><span class="line"><span class="comment"> * capable clocksource if the tick code is in oneshot</span></span><br><span class="line"><span class="comment"> * mode (highres or nohz)</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (!(cs-></span>flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {</span><br><span class="line"> <span class="comment">/* Override clocksource cannot be used. */</span></span><br><span class="line"> pr_warn(<span class="string">"Override clocksource %s is not HRT compatible - cannot switch while in HRT/NOHZ mode\n"</span>,</span><br><span class="line"> <span class="function"><span class="title">cs</span>-></span><span class="keyword">name</span>);</span><br><span class="line"> override_name[<span class="number">0</span>] = <span class="number">0</span>;</span><br><span class="line"> } <span class="keyword">else</span></span><br><span class="line"> <span class="comment">/* Override clocksource can be used. */</span></span><br><span class="line"> best = cs;</span><br><span class="line"> break;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.3.2) 通知timekeeper更新clocksource，tick-sched更新 */</span></span><br><span class="line"> <span class="keyword">if</span> (curr_clocksource != best && !timekeeping_notify(best)) {</span><br><span class="line"> <span class="function"><span class="title">pr_info</span>("Switched to clocksource %s\n", best-></span><span class="keyword">name</span>);</span><br><span class="line"> curr_clocksource = best;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line">||||→</span><br><span class="line">int timekeeping_notify(struct clocksource *clock)</span><br><span class="line">{</span><br><span class="line"> struct timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (tk-></span>tkr_mono.clock == clock)</span><br><span class="line"> return <span class="number">0</span>;</span><br><span class="line"> stop_machine(change_clocksource, clock, NULL);</span><br><span class="line"> tick_clock_notify();</span><br><span class="line"> <span class="function"><span class="title">return</span> tk-></span>tkr_mono.clock == clock ? <span class="number">0</span> : -<span class="number">1</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h4 id="2-1-1、exynos4-clocksource-init"><a href="#2-1-1、exynos4-clocksource-init" class="headerlink" title="2.1.1、exynos4_clocksource_init()"></a>2.1.1、exynos4_clocksource_init()</h4><p>exynos将global timer注册成clocksource，虽然global timer拥有64bit的位宽，但是注册的时候把其当成32bit的clocksource注册。</p>
<figure class="highlight arduino"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">static</span> u32 notrace <span class="title">exynos4_read_count_32</span><span class="params">(<span class="type">void</span>)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">readl_relaxed</span>(reg_base + EXYNOS4_MCT_G_CNT_L);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">static</span> <span class="type">cycle_t</span> <span class="title">exynos4_frc_read</span><span class="params">(<span class="keyword">struct</span> clocksource *cs)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">exynos4_read_count_32</span>();</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="keyword">struct</span> <span class="title class_">clocksource</span> mct_frc = {</span><br><span class="line"> .name = <span class="string">"mct-frc"</span>,</span><br><span class="line"> .rating = <span class="number">400</span>,</span><br><span class="line"> .read = exynos4_frc_read,</span><br><span class="line"> .mask = <span class="built_in">CLOCKSOURCE_MASK</span>(<span class="number">32</span>),</span><br><span class="line"> .flags = CLOCK_SOURCE_IS_CONTINUOUS,</span><br><span class="line"> .resume = exynos4_frc_resume,</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">static</span> <span class="type">void</span> __init <span class="title">exynos4_clocksource_init</span><span class="params">(<span class="type">void</span>)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="built_in">exynos4_mct_frc_start</span>();</span><br><span class="line"></span><br><span class="line"> exynos4_delay_timer.read_current_timer = &exynos4_read_current_timer;</span><br><span class="line"> exynos4_delay_timer.freq = clk_rate;</span><br><span class="line"> <span class="built_in">register_current_timer_delay</span>(&exynos4_delay_timer);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) exynos将global timer注册成clocksource */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">clocksource_register_hz</span>(&mct_frc, clk_rate))</span><br><span class="line"> <span class="built_in">panic</span>(<span class="string">"%s: can't register clocksource\n"</span>, mct_frc.name);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">sched_clock_register</span>(exynos4_read_sched_clock, <span class="number">32</span>, clk_rate);</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h3 id="2-2、timekeeper"><a href="#2-2、timekeeper" class="headerlink" title="2.2、timekeeper"></a>2.2、timekeeper</h3><p>timerkeeper提供了几种时间：xtime、monotonic time、raw monotonic time、boot time。</p>
<ul>
<li><strong>xtime</strong> 即是wall time，和RTC时间一样可以表示当前的时刻，它的起始时间是公元0世纪0秒，精度大于RTC时间；</li>
<li><strong>monotonic time</strong> 从系统开机后到现在的累计时间，不过不计算系统休眠的时间；</li>
<li><strong>raw monotonic time</strong> 和monotonic time含义一样，不过更纯粹，不会受到NTP时间调整的影响；</li>
<li><strong>boot time</strong> 在monotonic time的基础上加上了系统休眠的时间，它代表着系统上电后的总时间。</li>
</ul>
<table>
<thead>
<tr>
<th>时间种类</th>
<th>精度（统计单位）</th>
<th>访问速度</th>
<th>累计休眠时间</th>
<th>受NTP调整的影响</th>
<th>获取函数</th>
</tr>
</thead>
<tbody><tr>
<td>RTC</td>
<td>低</td>
<td>慢</td>
<td>Yes</td>
<td>Yes</td>
<td></td>
</tr>
<tr>
<td>xtime</td>
<td>高</td>
<td>快</td>
<td>Yes</td>
<td>Yes</td>
<td>do_gettimeofday()、ktime_get_real_ts()、ktime_get_real()</td>
</tr>
<tr>
<td>monotonic</td>
<td>高</td>
<td>快</td>
<td>No</td>
<td>Yes</td>
<td>ktime_get()、ktime_get_ts64()</td>
</tr>
<tr>
<td>raw monotonic</td>
<td>高</td>
<td>快</td>
<td>No</td>
<td>No</td>
<td>ktime_get_raw()、getrawmonotonic64()</td>
</tr>
<tr>
<td>boot time</td>
<td>高</td>
<td>快</td>
<td>Yes</td>
<td>Yes</td>
<td>ktime_get_boottime()</td>
</tr>
</tbody></table>
<h4 id="2-2-1、timekeeper的定义"><a href="#2-2-1、timekeeper的定义" class="headerlink" title="2.2.1、timekeeper的定义"></a>2.2.1、timekeeper的定义</h4><p>虽然clocksource定时器只有一个，但是timekeeper提供了xtime、monotonic time、raw time、boot time等几种时间，所以timekeeper结构体中定义了多个变量来记住这些差值。</p>
<figure class="highlight zephir"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * struct timekeeper - Structure holding internal timekeeping values.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@tkr</span>_mono: The readout base structure for CLOCK_MONOTONIC</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@tkr</span>_raw: The readout base structure for CLOCK_MONOTONIC_RAW</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@xtime</span>_sec: Current CLOCK_REALTIME time in seconds</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ktime</span>_sec: Current CLOCK_MONOTONIC time in seconds</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@wall</span>_to_monotonic: CLOCK_REALTIME to CLOCK_MONOTONIC offset</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@offs</span>_real: Offset clock monotonic -> clock realtime</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@offs</span>_boot: Offset clock monotonic -> clock boottime</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@offs</span>_tai: Offset clock monotonic -> clock tai</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@tai</span>_offset: The current UTC to TAI offset in seconds</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@clock</span>_was_set_seq: The sequence number of clock was set events</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@next</span>_leap_ktime: CLOCK_MONOTONIC time value of a pending leap-second</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@raw</span>_time: Monotonic raw base time in timespec64 format</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@cycle</span>_interval: Number of clock cycles in one NTP interval</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@xtime</span>_interval: Number of clock shifted nano seconds in one NTP</span></span><br><span class="line"><span class="comment"> * interval.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@xtime</span>_remainder: Shifted nano seconds left over when rounding</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@cycle</span>_interval</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@raw</span>_interval: Raw nano seconds accumulated per NTP interval.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ntp</span>_error: Difference between accumulated time and NTP time in ntp</span></span><br><span class="line"><span class="comment"> * shifted nano seconds.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ntp</span>_error_shift: Shift conversion between clock shifted nano seconds and</span></span><br><span class="line"><span class="comment"> * ntp shifted nano seconds.</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@last</span>_warning: Warning ratelimiter (DEBUG_TIMEKEEPING)</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@underflow</span>_seen: Underflow warning flag (DEBUG_TIMEKEEPING)</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@overflow</span>_seen: Overflow warning flag (DEBUG_TIMEKEEPING)</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * Note: For timespec(64) based interfaces wall_to_monotonic is what</span></span><br><span class="line"><span class="comment"> * we need to add to xtime (or xtime corrected for sub jiffie times)</span></span><br><span class="line"><span class="comment"> * to get to monotonic time. Monotonic is pegged at zero at system</span></span><br><span class="line"><span class="comment"> * boot time, so wall_to_monotonic will be negative, however, we will</span></span><br><span class="line"><span class="comment"> * ALWAYS keep the tv_nsec part positive so we can use the usual</span></span><br><span class="line"><span class="comment"> * normalization.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * wall_to_monotonic is moved after resume from suspend for the</span></span><br><span class="line"><span class="comment"> * monotonic time not to jump. We need to add total_sleep_time to</span></span><br><span class="line"><span class="comment"> * wall_to_monotonic to get the real boot based time offset.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * wall_to_monotonic is no longer the boot time, getboottime must be</span></span><br><span class="line"><span class="comment"> * used instead.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line">struct timekeeper {</span><br><span class="line"> struct tk_read_base tkr_mono; </span><br><span class="line"> <span class="comment">// tkr_mono.xtime_nsec：xtime/monotonic time 的ns</span></span><br><span class="line"> <span class="comment">// tkr_mono.base：monotonic time的base部分</span></span><br><span class="line"> struct tk_read_base tkr_raw;</span><br><span class="line"> <span class="comment">// tkr_mono.base：raw time的base部分</span></span><br><span class="line"> u64 xtime_sec; <span class="comment">// xtime的sec</span></span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">long</span> ktime_sec; <span class="comment">// monotonic time 的整sec</span></span><br><span class="line"> struct timespec64 wall_to_monotonic; <span class="comment">// xtime + wall_to_monotonic = monotonic time</span></span><br><span class="line"> ktime_t offs_real; <span class="comment">// monotonic time + offs_real = xtime，</span></span><br><span class="line"> <span class="comment">// 和wall_to_monotonic是相反的值</span></span><br><span class="line"> ktime_t offs_boot; <span class="comment">// monotonic time + offs_boot = boot time</span></span><br><span class="line"> ktime_t offs_tai;</span><br><span class="line"> s32 tai_offset;</span><br><span class="line"> <span class="keyword">unsigned</span> <span class="keyword">int</span> clock_was_set_seq;</span><br><span class="line"> ktime_t next_leap_ktime;</span><br><span class="line"> struct timespec64 raw_time; <span class="comment">// raw time</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">/* The following members are for timekeeping internal use */</span></span><br><span class="line"> cycle_t cycle_interval;</span><br><span class="line"> u64 xtime_interval;</span><br><span class="line"> s64 xtime_remainder;</span><br><span class="line"> u32 raw_interval;</span><br><span class="line"> <span class="comment">/* The ntp_tick_length() value currently being used.</span></span><br><span class="line"><span class="comment"> * This cached copy ensures we consistently apply the tick</span></span><br><span class="line"><span class="comment"> * length for an entire tick, as ntp_tick_length may change</span></span><br><span class="line"><span class="comment"> * mid-tick, and we don't want to apply that new value to</span></span><br><span class="line"><span class="comment"> * the tick in progress.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> u64 ntp_tick;</span><br><span class="line"> <span class="comment">/* Difference between accumulated time and NTP time in ntp</span></span><br><span class="line"><span class="comment"> * shifted nano seconds. */</span></span><br><span class="line"> s64 ntp_error;</span><br><span class="line"> u32 ntp_error_shift;</span><br><span class="line"> u32 ntp_err_mult;</span><br><span class="line">#ifdef CONFIG_DEBUG_TIMEKEEPING</span><br><span class="line"> <span class="keyword">long</span> last_warning;</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * These simple flag variables are managed</span></span><br><span class="line"><span class="comment"> * without locks, which is racy, but they are</span></span><br><span class="line"><span class="comment"> * ok since we don't really care about being</span></span><br><span class="line"><span class="comment"> * super precise about how many events were</span></span><br><span class="line"><span class="comment"> * seen, just that a problem was observed.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">int</span> underflow_seen;</span><br><span class="line"> <span class="keyword">int</span> overflow_seen;</span><br><span class="line">#endif</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<h4 id="2-2-2、timekeeper的初始化"><a href="#2-2-2、timekeeper的初始化" class="headerlink" title="2.2.2、timekeeper的初始化"></a>2.2.2、timekeeper的初始化</h4><p>timekeeper在初始化的过程中，读取当前的RTC值和clocksource的值，来初始化xtime、monotonic time、raw time、boot time，以及各种offset。</p>
<figure class="highlight sas"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br></pre></td><td class="code"><pre><span class="line">void __init timekeeping_init(void)</span><br><span class="line">{</span><br><span class="line"> struct timekeeper <span class="comment">*tk = &tk_core.timekeeper;</span></span><br><span class="line"> struct clocksource <span class="comment">*clock;</span></span><br><span class="line"> unsigned long flags;</span><br><span class="line"> struct timespec64 now, boot, tmp;</span><br><span class="line"></span><br><span class="line"> read_persistent_clock64(<span class="variable">&now</span>);</span><br><span class="line"> <span class="keyword">if</span> (!timespec64_valid_strict(<span class="variable">&now</span>)) {</span><br><span class="line"> pr_war<span class="meta">n</span>(<span class="string">"WARNING: Persistent clock returned invalid value!\n"</span></span><br><span class="line"> <span class="string">" Check your CMOS/BIOS settings.\n"</span>);</span><br><span class="line"> now.tv_sec = 0;</span><br><span class="line"> now.tv_nsec = 0;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (now.tv_sec || now.tv_nsec)</span><br><span class="line"> persistent_clock_exists = true;</span><br><span class="line"></span><br><span class="line"> read_boot_clock64(<span class="variable">&boot</span>);</span><br><span class="line"> <span class="keyword">if</span> (!timespec64_valid_strict(<span class="variable">&boot</span>)) {</span><br><span class="line"> pr_war<span class="meta">n</span>(<span class="string">"WARNING: Boot clock returned invalid value!\n"</span></span><br><span class="line"> <span class="string">" Check your CMOS/BIOS settings.\n"</span>);</span><br><span class="line"> boot.tv_sec = 0;</span><br><span class="line"> boot.tv_nsec = 0;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> raw_spin_lock_irqsave(<span class="variable">&timekeeper_lock</span>, flags);</span><br><span class="line"> write_seqcount_begi<span class="meta">n</span>(<span class="variable">&tk_core.</span>seq);</span><br><span class="line"> ntp_init();</span><br><span class="line"></span><br><span class="line"> clock = clocksource_default_clock();</span><br><span class="line"> <span class="keyword">if</span> (clock->enable)</span><br><span class="line"> clock->enable(clock);</span><br><span class="line"> tk_setup_internals(tk, clock);</span><br><span class="line"></span><br><span class="line"> tk_set_x<span class="meta">time</span>(tk, <span class="variable">&now</span>);</span><br><span class="line"> tk->raw_time.tv_sec = 0;</span><br><span class="line"> tk->raw_time.tv_nsec = 0;</span><br><span class="line"> <span class="keyword">if</span> (boot.tv_sec == 0 <span class="variable">&&</span> boot.tv_nsec == 0)</span><br><span class="line"> boot = tk_x<span class="meta">time</span>(tk);</span><br><span class="line"></span><br><span class="line"> set_normalized_timespec64(<span class="variable">&tmp</span>, -boot.tv_sec, -boot.tv_nsec);</span><br><span class="line"> tk_set_wall_to_mono(tk, tmp);</span><br><span class="line"></span><br><span class="line"> timekeeping_up<span class="meta">date</span>(tk, TK_MIRROR | TK_CLOCK_WAS_SET);</span><br><span class="line"></span><br><span class="line"> write_seqcount_end(<span class="variable">&tk_core.</span>seq);</span><br><span class="line"> raw_spin_unlock_irqrestore(<span class="variable">&timekeeper_lock</span>, flags);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>timekeeper原理上的初始化是在timekeeping_init()函数中完成的，但是read_persistent_clock64()、read_boot_clock64()都是空函数，所以实际上的初始化是另外的路径：rtc_hctosys() -> do_settimeofday64()，rtc初始化的时候重新配置timekeeper。</p>
<figure class="highlight sas"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br></pre></td><td class="code"><pre><span class="line">static int __init rtc_hctosys(void)</span><br><span class="line">{</span><br><span class="line"> int err = -ENODEV;</span><br><span class="line"> struct rtc_time tm;</span><br><span class="line"> struct timespec64 tv64 = {</span><br><span class="line"> .tv_nsec = NSEC_PER_SEC >> 1,</span><br><span class="line"> };</span><br><span class="line"> struct rtc_device <span class="comment">*rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE);</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (rtc == <span class="keyword">NULL</span>) {</span><br><span class="line"> pr_info(<span class="string">"unable to open rtc device (%s)\n"</span>,</span><br><span class="line"> CONFIG_RTC_HCTOSYS_DEVICE);</span><br><span class="line"> <span class="keyword">goto</span> err_open;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 读取当前的rtc时间 */</span></span><br><span class="line"> err = rtc_read_<span class="meta">time</span>(rtc, <span class="variable">&tm</span>);</span><br><span class="line"> <span class="keyword">if</span> (err) {</span><br><span class="line"> dev_err(rtc->dev.parent,</span><br><span class="line"> <span class="string">"hctosys: unable to read the hardware clock\n"</span>);</span><br><span class="line"> <span class="keyword">goto</span> err_read;</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> tv64.tv_sec = rtc_tm_to_time64(<span class="variable">&tm</span>);</span><br><span class="line"> tv64.tv_nsec = tm.tm_cnt <span class="comment">* (1000000000 / 32768);</span></span><br><span class="line"> </span><br><span class="line"> <span class="comment">/* (2) 根据rtc时间配置xtime */</span></span><br><span class="line"> err = do_settimeofday64(<span class="variable">&tv64</span>);</span><br><span class="line"></span><br><span class="line"> dev_info(rtc->dev.parent,</span><br><span class="line"> <span class="string">"setting system clock to "</span></span><br><span class="line"> <span class="string">"%d-%02d-%02d %02d:%02d:%02d UTC (%lld)\n"</span>,</span><br><span class="line"> tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,</span><br><span class="line"> tm.tm_hour, tm.tm_min, tm.tm_sec,</span><br><span class="line"> (long long) tv64.tv_sec);</span><br><span class="line"></span><br><span class="line">err_read:</span><br><span class="line"> rtc_class_<span class="meta">close</span>(rtc);</span><br><span class="line"></span><br><span class="line">err_open:</span><br><span class="line"> rtc_hctosys_ret = err;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> err;</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">int do_settimeofday64(const struct timespec64 <span class="comment">*ts)</span></span><br><span class="line"><span class="comment">{</span></span><br><span class="line"><span class="comment"> struct timekeeper *tk = &tk_core.timekeeper;</span></span><br><span class="line"> struct timespec64 ts_delta, xt;</span><br><span class="line"> unsigned long flags;</span><br><span class="line"> int ret = 0;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!timespec64_valid_strict(ts))</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> raw_spin_lock_irqsave(<span class="variable">&timekeeper_lock</span>, flags);</span><br><span class="line"> write_seqcount_begi<span class="meta">n</span>(<span class="variable">&tk_core.</span>seq);</span><br><span class="line"></span><br><span class="line"> timekeeping_forward_now(tk);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.1) 读取当前的xtime，计算rtc time和xtime之间的差值 */</span></span><br><span class="line"> xt = tk_x<span class="meta">time</span>(tk);</span><br><span class="line"> ts_delta.tv_sec = ts->tv_sec - xt.tv_sec;</span><br><span class="line"> ts_delta.tv_nsec = ts->tv_nsec - xt.tv_nsec;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (timespec64_compare(<span class="variable">&tk</span>->wall_to_monotonic, <span class="variable">&ts_delta</span>) > 0) {</span><br><span class="line"> ret = -EINVAL;</span><br><span class="line"> <span class="keyword">goto</span> <span class="keyword">out</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.2) 将差值追加到offset；tk->wall_to_monotonic、tk->offs_real */</span></span><br><span class="line"> tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta));</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.3) 更新xtime */</span></span><br><span class="line"> tk_set_x<span class="meta">time</span>(tk, ts);</span><br><span class="line"><span class="keyword">out</span>:</span><br><span class="line"> timekeeping_up<span class="meta">date</span>(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);</span><br><span class="line"></span><br><span class="line"> write_seqcount_end(<span class="variable">&tk_core.</span>seq);</span><br><span class="line"> raw_spin_unlock_irqrestore(<span class="variable">&timekeeper_lock</span>, flags);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* signal hrtimers about time change */</span></span><br><span class="line"> clock_was_set();</span><br><span class="line"> notify_time_up<span class="meta">date</span>();</span><br><span class="line"> <span class="keyword">return</span> ret;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h4 id="2-2-3、timekeeper的update"><a href="#2-2-3、timekeeper的update" class="headerlink" title="2.2.3、timekeeper的update"></a>2.2.3、timekeeper的update</h4><p>clocksource定时器的值要定时的读出来，并且把增量加到timekeeper中，不然clocksource定时器会溢出。这个定时更新的时间一般是1 tick，调用的函数是update_wall_time()：</p>
<figure class="highlight rust"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span 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class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br><span class="line">185</span><br><span class="line">186</span><br><span class="line">187</span><br><span class="line">188</span><br><span class="line">189</span><br><span class="line">190</span><br><span class="line">191</span><br><span class="line">192</span><br><span class="line">193</span><br><span class="line">194</span><br><span class="line">195</span><br><span class="line">196</span><br><span class="line">197</span><br><span class="line">198</span><br><span class="line">199</span><br><span class="line">200</span><br></pre></td><td class="code"><pre><span class="line">void <span class="title function_ invoke__">update_wall_time</span>(void)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timekeeper</span> *real_tk = &tk_core.timekeeper;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk = &shadow_timekeeper;</span><br><span class="line"> cycle_t offset;</span><br><span class="line"> int shift = <span class="number">0</span>, maxshift;</span><br><span class="line"> unsigned int clock_set = <span class="number">0</span>;</span><br><span class="line"> unsigned long flags;</span><br><span class="line"></span><br><span class="line"> <span class="title function_ invoke__">raw_spin_lock_irqsave</span>(&timekeeper_lock, flags);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Make sure we're fully resumed: */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="title function_ invoke__">unlikely</span>(timekeeping_suspended))</span><br><span class="line"> goto out;</span><br><span class="line"></span><br><span class="line">#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET</span><br><span class="line"> offset = real_tk<span class="punctuation">-></span>cycle_interval;</span><br><span class="line">#<span class="keyword">else</span></span><br><span class="line"> <span class="comment">/* (1) 获取clocksource和上一次update之间的offset */</span></span><br><span class="line"> offset = <span class="title function_ invoke__">clocksource_delta</span>(tk<span class="punctuation">-></span>tkr_mono.<span class="title function_ invoke__">read</span>(tk<span class="punctuation">-></span>tkr_mono.clock),</span><br><span class="line"> tk<span class="punctuation">-></span>tkr_mono.cycle_last, tk<span class="punctuation">-></span>tkr_mono.mask);</span><br><span class="line">#endif</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Check if there's really nothing to do */</span></span><br><span class="line"> <span class="keyword">if</span> (offset < real_tk<span class="punctuation">-></span>cycle_interval)</span><br><span class="line"> goto out;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Do some additional sanity checking */</span></span><br><span class="line"> <span class="title function_ invoke__">timekeeping_check_update</span>(real_tk, offset);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * With NO_HZ we may have to accumulate many cycle_intervals</span></span><br><span class="line"><span class="comment"> * (think "ticks") worth of time at once. To do this efficiently,</span></span><br><span class="line"><span class="comment"> * we calculate the largest doubling multiple of cycle_intervals</span></span><br><span class="line"><span class="comment"> * that is smaller than the offset. We then accumulate that</span></span><br><span class="line"><span class="comment"> * chunk in one go, and then try to consume the next smaller</span></span><br><span class="line"><span class="comment"> * doubled multiple.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> shift = <span class="title function_ invoke__">ilog2</span>(offset) - <span class="title function_ invoke__">ilog2</span>(tk<span class="punctuation">-></span>cycle_interval);</span><br><span class="line"> shift = <span class="title function_ invoke__">max</span>(<span class="number">0</span>, shift);</span><br><span class="line"> <span class="comment">/* Bound shift to one less than what overflows tick_length */</span></span><br><span class="line"> maxshift = (<span class="number">64</span> - (<span class="title function_ invoke__">ilog2</span>(<span class="title function_ invoke__">ntp_tick_length</span>())+<span class="number">1</span>)) - <span class="number">1</span>;</span><br><span class="line"> shift = <span class="title function_ invoke__">min</span>(shift, maxshift);</span><br><span class="line"> <span class="comment">/* (2) 如果offset的值是多个cycle_interval，</span></span><br><span class="line"><span class="comment"> 不要一次update，使用2的n次方cycle_interval的方式逐个update。</span></span><br><span class="line"><span class="comment"> tk->cycle_interval的值在tk_setup_internals()时被赋值，默认为1 tick */</span></span><br><span class="line"> <span class="keyword">while</span> (offset >= tk<span class="punctuation">-></span>cycle_interval) {</span><br><span class="line"> <span class="comment">/* (3) 将offset更新到timekeeper中 */</span></span><br><span class="line"> offset = <span class="title function_ invoke__">logarithmic_accumulation</span>(tk, offset, shift,</span><br><span class="line"> &clock_set);</span><br><span class="line"> <span class="keyword">if</span> (offset < tk<span class="punctuation">-></span>cycle_interval<<shift)</span><br><span class="line"> shift--;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* correct the clock when NTP error is too big */</span></span><br><span class="line"> <span class="title function_ invoke__">timekeeping_adjust</span>(tk, offset);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * XXX This can be killed once everyone converts</span></span><br><span class="line"><span class="comment"> * to the new update_vsyscall.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="title function_ invoke__">old_vsyscall_fixup</span>(tk);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Finally, make sure that after the rounding</span></span><br><span class="line"><span class="comment"> * xtime_nsec isn't larger than NSEC_PER_SEC</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> clock_set |= <span class="title function_ invoke__">accumulate_nsecs_to_secs</span>(tk);</span><br><span class="line"></span><br><span class="line"> <span class="title function_ invoke__">write_seqcount_begin</span>(&tk_core.seq);</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Update the real timekeeper.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * We could avoid this memcpy by switching pointers, but that</span></span><br><span class="line"><span class="comment"> * requires changes to all other timekeeper usage sites as</span></span><br><span class="line"><span class="comment"> * well, i.e. move the timekeeper pointer getter into the</span></span><br><span class="line"><span class="comment"> * spinlocked/seqcount protected sections. And we trade this</span></span><br><span class="line"><span class="comment"> * memcpy under the tk_core.seq against one before we start</span></span><br><span class="line"><span class="comment"> * updating.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (4) */</span></span><br><span class="line"> <span class="title function_ invoke__">timekeeping_update</span>(tk, clock_set);</span><br><span class="line"> <span class="title function_ invoke__">memcpy</span>(real_tk, tk, <span class="title function_ invoke__">sizeof</span>(*tk));</span><br><span class="line"> <span class="comment">/* The memcpy must come last. Do not put anything here! */</span></span><br><span class="line"> <span class="title function_ invoke__">write_seqcount_end</span>(&tk_core.seq);</span><br><span class="line">out:</span><br><span class="line"> <span class="title function_ invoke__">raw_spin_unlock_irqrestore</span>(&timekeeper_lock, flags);</span><br><span class="line"> <span class="keyword">if</span> (clock_set)</span><br><span class="line"> <span class="comment">/* Have to call _delayed version, since in irq context*/</span></span><br><span class="line"> <span class="title function_ invoke__">clock_was_set_delayed</span>();</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line"><span class="keyword">static</span> cycle_t <span class="title function_ invoke__">logarithmic_accumulation</span>(<span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk, cycle_t offset,</span><br><span class="line"> <span class="type">u32</span> shift,</span><br><span class="line"> unsigned int *clock_set)</span><br><span class="line">{</span><br><span class="line"> cycle_t interval = tk<span class="punctuation">-></span>cycle_interval << shift;</span><br><span class="line"> <span class="type">u64</span> raw_nsecs;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* If the offset is smaller than a shifted interval, do nothing */</span></span><br><span class="line"> <span class="keyword">if</span> (offset < interval)</span><br><span class="line"> <span class="keyword">return</span> offset;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Accumulate one shifted interval */</span></span><br><span class="line"> offset -= interval;</span><br><span class="line"> <span class="comment">/* (3.1) 更新cycle_last */</span></span><br><span class="line"> tk<span class="punctuation">-></span>tkr_mono.cycle_last += interval;</span><br><span class="line"> tk<span class="punctuation">-></span>tkr_raw.cycle_last += interval;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (3.2) 更新xtime：</span></span><br><span class="line"><span class="comment"> tk->tkr_mono.xtime_nsec</span></span><br><span class="line"><span class="comment"> tk->xtime_sec */</span></span><br><span class="line"> tk<span class="punctuation">-></span>tkr_mono.xtime_nsec += tk<span class="punctuation">-></span>xtime_interval << shift;</span><br><span class="line"> *clock_set |= <span class="title function_ invoke__">accumulate_nsecs_to_secs</span>(tk);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Accumulate raw time */</span></span><br><span class="line"> <span class="comment">/* (3.3) 更新raw time：</span></span><br><span class="line"><span class="comment"> tk->raw_time.tv_nsec</span></span><br><span class="line"><span class="comment"> tk->raw_time.tv_sec */</span></span><br><span class="line"> raw_nsecs = (<span class="type">u64</span>)tk<span class="punctuation">-></span>raw_interval << shift;</span><br><span class="line"> raw_nsecs += tk<span class="punctuation">-></span>raw_time.tv_nsec;</span><br><span class="line"> <span class="keyword">if</span> (raw_nsecs >= NSEC_PER_SEC) {</span><br><span class="line"> <span class="type">u64</span> raw_secs = raw_nsecs;</span><br><span class="line"> raw_nsecs = <span class="title function_ invoke__">do_div</span>(raw_secs, NSEC_PER_SEC);</span><br><span class="line"> tk<span class="punctuation">-></span>raw_time.tv_sec += raw_secs;</span><br><span class="line"> }</span><br><span class="line"> tk<span class="punctuation">-></span>raw_time.tv_nsec = raw_nsecs;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Accumulate error between NTP and clock interval */</span></span><br><span class="line"> tk<span class="punctuation">-></span>ntp_error += tk<span class="punctuation">-></span>ntp_tick << shift;</span><br><span class="line"> tk<span class="punctuation">-></span>ntp_error -= (tk<span class="punctuation">-></span>xtime_interval + tk<span class="punctuation">-></span>xtime_remainder) <<</span><br><span class="line"> (tk<span class="punctuation">-></span>ntp_error_shift + shift);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> offset;</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line"><span class="keyword">static</span> void <span class="title function_ invoke__">timekeeping_update</span>(<span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk, unsigned int action)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">if</span> (action & TK_CLEAR_NTP) {</span><br><span class="line"> tk<span class="punctuation">-></span>ntp_error = <span class="number">0</span>;</span><br><span class="line"> <span class="title function_ invoke__">ntp_clear</span>();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="title function_ invoke__">tk_update_leap_state</span>(tk);</span><br><span class="line"> <span class="comment">/* (4.1) update monotonic time */</span></span><br><span class="line"> <span class="title function_ invoke__">tk_update_ktime_data</span>(tk);</span><br><span class="line"></span><br><span class="line"> <span class="title function_ invoke__">update_vsyscall</span>(tk);</span><br><span class="line"> <span class="title function_ invoke__">update_pvclock_gtod</span>(tk, action & TK_CLOCK_WAS_SET);</span><br><span class="line"></span><br><span class="line"> <span class="title function_ invoke__">update_fast_timekeeper</span>(&tk<span class="punctuation">-></span>tkr_mono, &tk_fast_mono);</span><br><span class="line"> <span class="title function_ invoke__">update_fast_timekeeper</span>(&tk<span class="punctuation">-></span>tkr_raw, &tk_fast_raw);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (action & TK_CLOCK_WAS_SET)</span><br><span class="line"> tk<span class="punctuation">-></span>clock_was_set_seq++;</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * The mirroring of the data to the shadow-timekeeper needs</span></span><br><span class="line"><span class="comment"> * to happen last here to ensure we don't over-write the</span></span><br><span class="line"><span class="comment"> * timekeeper structure on the next update with stale data</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (action & TK_MIRROR)</span><br><span class="line"> <span class="title function_ invoke__">memcpy</span>(&shadow_timekeeper, &tk_core.timekeeper,</span><br><span class="line"> <span class="title function_ invoke__">sizeof</span>(tk_core.timekeeper));</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line"><span class="keyword">static</span> inline void <span class="title function_ invoke__">tk_update_ktime_data</span>(<span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk)</span><br><span class="line">{</span><br><span class="line"> <span class="type">u64</span> seconds;</span><br><span class="line"> <span class="type">u32</span> nsec;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * The xtime based monotonic readout is:</span></span><br><span class="line"><span class="comment"> * nsec = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec + now();</span></span><br><span class="line"><span class="comment"> * The ktime based monotonic readout is:</span></span><br><span class="line"><span class="comment"> * nsec = base_mono + now();</span></span><br><span class="line"><span class="comment"> * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (4.1.1) update tk->tkr_mono.base的值，</span></span><br><span class="line"><span class="comment"> = tk->xtime_sec + tk->wall_to_monotonic,</span></span><br><span class="line"><span class="comment"> tk->tkr_mono.xtime_nsec 没有计算到base中 */</span></span><br><span class="line"> seconds = (<span class="type">u64</span>)(tk<span class="punctuation">-></span>xtime_sec + tk<span class="punctuation">-></span>wall_to_monotonic.tv_sec);</span><br><span class="line"> nsec = (<span class="type">u32</span>) tk<span class="punctuation">-></span>wall_to_monotonic.tv_nsec;</span><br><span class="line"> tk<span class="punctuation">-></span>tkr_mono.base = <span class="title function_ invoke__">ns_to_ktime</span>(seconds * NSEC_PER_SEC + nsec);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Update the monotonic raw base */</span></span><br><span class="line"> <span class="comment">/* (4.1.2) update tk->tkr_raw.base的值，</span></span><br><span class="line"><span class="comment"> 直接转换tk->raw_time */</span></span><br><span class="line"> tk<span class="punctuation">-></span>tkr_raw.base = <span class="title function_ invoke__">timespec64_to_ktime</span>(tk<span class="punctuation">-></span>raw_time);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * The sum of the nanoseconds portions of xtime and</span></span><br><span class="line"><span class="comment"> * wall_to_monotonic can be greater/equal one second. Take</span></span><br><span class="line"><span class="comment"> * this into account before updating tk->ktime_sec.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (4.1.3) update tk->ktime_sec的值</span></span><br><span class="line"><span class="comment"> nsec += (u32)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);</span></span><br><span class="line"><span class="comment"> if (nsec >= NSEC_PER_SEC)</span></span><br><span class="line"><span class="comment"> seconds++;</span></span><br><span class="line"><span class="comment"> tk->ktime_sec = seconds;</span></span><br><span class="line"><span class="comment">}</span></span><br></pre></td></tr></table></figure>
<h4 id="2-2-4、timekeeper的获取"><a href="#2-2-4、timekeeper的获取" class="headerlink" title="2.2.4、timekeeper的获取"></a>2.2.4、timekeeper的获取</h4><ul>
<li><strong>xtime/wall time 的获取:</strong></li>
</ul>
<p>do_gettimeofday()、ktime_get_real_ts()最后调用的getnstimeofday64() -> __getnstimeofday64()获取到xtime：</p>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br></pre></td><td class="code"><pre><span class="line">int __getnstimeofday64(struct timespec64 *ts)</span><br><span class="line">{</span><br><span class="line"> struct timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> unsigned long seq;</span><br><span class="line"> s64 nsecs = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) sec直接从变量tk->xtime_sec获取到，</span></span><br><span class="line"><span class="comment"> 即上一tick更新的值 */</span></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span><span class="function"><span class="title">tv_sec</span> = tk-></span>xtime_sec;</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/* (2) nsec需要更新最新的值：tk->tkr_mono.xtime_nsec + delta</span></span><br><span class="line"><span class="comment"> delta是距离上一次tick更新的差值 */</span></span><br><span class="line"> <span class="function"><span class="title">nsecs</span> = timekeeping_get_ns(&tk-></span>tkr_mono);</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>tv_nsec = <span class="number">0</span>;</span><br><span class="line"> timespec64_add_ns(ts, nsecs);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Do not bail out early, in case there were callers still using</span></span><br><span class="line"><span class="comment"> * the value, even in the face of the WARN_ON.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (unlikely(timekeeping_suspended))</span><br><span class="line"> return -EAGAIN;</span><br><span class="line"> return <span class="number">0</span>;</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)</span><br><span class="line">{</span><br><span class="line"> cycle_t delta;</span><br><span class="line"> s64 nsec;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.1) 获取距离上一次tick更新，timer的delta值 */</span></span><br><span class="line"> delta = timekeeping_get_delta(tkr);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.2) delta加上上一次的nsec tkr->xtime_nsec，</span></span><br><span class="line"><span class="comment"> 即为最新的ns值 */</span></span><br><span class="line"> <span class="function"><span class="title">nsec</span> = (delta * tkr-></span><span class="function"><span class="title">mult</span> + tkr-></span><span class="function"><span class="title">xtime_nsec</span>) >> tkr-></span>shift;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* If arch requires, add in get_arch_timeoffset() */</span></span><br><span class="line"> return nsec + arch_gettimeoffset();</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line">static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)</span><br><span class="line">{</span><br><span class="line"> struct timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> cycle_t now, last, mask, max, delta;</span><br><span class="line"> unsigned int seq;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Since we're called holding a seqlock, the data may shift</span></span><br><span class="line"><span class="comment"> * under us while we're doing the calculation. This can cause</span></span><br><span class="line"><span class="comment"> * false positives, since we'd note a problem but throw the</span></span><br><span class="line"><span class="comment"> * results away. So nest another seqlock here to atomically</span></span><br><span class="line"><span class="comment"> * grab the points we are checking with.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"> <span class="comment">/* (2.1.1) 使用read函数读取当前timer的计数 */</span></span><br><span class="line"> <span class="function"><span class="title">now</span> = tkr-></span><span class="function"><span class="title">read</span>(tkr-></span>clock);</span><br><span class="line"> <span class="function"><span class="title">last</span> = tkr-></span>cycle_last;</span><br><span class="line"> <span class="function"><span class="title">mask</span> = tkr-></span>mask;</span><br><span class="line"> <span class="function"><span class="title">max</span> = tkr-></span><span class="function"><span class="title">clock</span>-></span>max_cycles;</span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.1.2) 使用公式：(now - last) & mask，</span></span><br><span class="line"><span class="comment"> 计算delta值 */</span></span><br><span class="line"> delta = clocksource_delta(now, last, mask);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Try to catch underflows by checking if we are seeing small</span></span><br><span class="line"><span class="comment"> * mask-relative negative values.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (unlikely((~delta & mask) < (mask >> <span class="number">3</span>))) {</span><br><span class="line"> <span class="function"><span class="title">tk</span>-></span>underflow_seen = <span class="number">1</span>;</span><br><span class="line"> delta = <span class="number">0</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Cap delta value to the max_cycles values to avoid mult overflows */</span></span><br><span class="line"> <span class="keyword">if</span> (unlikely(delta > max)) {</span><br><span class="line"> <span class="function"><span class="title">tk</span>-></span>overflow_seen = <span class="number">1</span>;</span><br><span class="line"> <span class="function"><span class="title">delta</span> = tkr-></span><span class="function"><span class="title">clock</span>-></span>max_cycles;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> return delta;</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<p>ktime_get_real()使用monotonic time再加上差值timekeeper.offs_real的方法来获取xtime：</p>
<figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">static</span> inline ktime_t <span class="title">ktime_get_real</span>(<span class="params"><span class="keyword">void</span></span>)</span></span><br><span class="line">{</span><br><span class="line"> <span class="keyword">return</span> ktime_get_with_offset(TK_OFFS_REAL);</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line"><span class="keyword">static</span> ktime_t *offsets[TK_OFFS_MAX] = {</span><br><span class="line"> [<span class="meta">TK_OFFS_REAL</span>] = &tk_core.timekeeper.offs_real,</span><br><span class="line"> [<span class="meta">TK_OFFS_BOOT</span>] = &tk_core.timekeeper.offs_boot,</span><br><span class="line"> [<span class="meta">TK_OFFS_TAI</span>] = &tk_core.timekeeper.offs_tai,</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="function">ktime_t <span class="title">ktime_get_with_offset</span>(<span class="params"><span class="built_in">enum</span> tk_offsets offs</span>)</span></span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> unsigned <span class="built_in">int</span> seq;</span><br><span class="line"> ktime_t <span class="keyword">base</span>, *offset = offsets[offs];</span><br><span class="line"> s64 nsecs;</span><br><span class="line"></span><br><span class="line"> WARN_ON(timekeeping_suspended);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"> <span class="comment">/* (1) monotonic time = tk->tkr_mono.base，</span></span><br><span class="line"><span class="comment"> offset = timekeeper.offs_real */</span></span><br><span class="line"> <span class="keyword">base</span> = ktime_add(tk->tkr_mono.<span class="keyword">base</span>, *offset);</span><br><span class="line"> <span class="comment">/* (2) nsec需要更新最新的值：tk->tkr_mono.xtime_nsec + delta</span></span><br><span class="line"><span class="comment"> delta是距离上一次tick更新的差值 */</span></span><br><span class="line"> nsecs = timekeeping_get_ns(&tk->tkr_mono);</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ktime_add_ns(<span class="keyword">base</span>, nsecs);</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li><strong>monotonic time 的获取；</strong></li>
</ul>
<p>ktime_get()直接获取monotonic time：</p>
<figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="function">ktime_t <span class="title">ktime_get</span>(<span class="params"><span class="keyword">void</span></span>)</span></span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> unsigned <span class="built_in">int</span> seq;</span><br><span class="line"> ktime_t <span class="keyword">base</span>;</span><br><span class="line"> s64 nsecs;</span><br><span class="line"></span><br><span class="line"> WARN_ON(timekeeping_suspended);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"> <span class="comment">/* (1) monotonic time = tk->tkr_mono.base */</span></span><br><span class="line"> <span class="keyword">base</span> = tk->tkr_mono.<span class="keyword">base</span>;</span><br><span class="line"> <span class="comment">/* (2) nsec需要更新最新的值：tk->tkr_mono.xtime_nsec + delta</span></span><br><span class="line"><span class="comment"> delta是距离上一次tick更新的差值 */</span></span><br><span class="line"> nsecs = timekeeping_get_ns(&tk->tkr_mono);</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ktime_add_ns(<span class="keyword">base</span>, nsecs);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>ktime_get_ts64()通过xtime加上差值tk->wall_to_monotonic的方法来获取monotonic time：</p>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line">void ktime_get_ts64(struct timespec64 *ts)</span><br><span class="line">{</span><br><span class="line"> struct timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> struct timespec64 tomono;</span><br><span class="line"> s64 nsec;</span><br><span class="line"> unsigned int seq;</span><br><span class="line"></span><br><span class="line"> WARN_ON(timekeeping_suspended);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"> <span class="comment">/* (1) 获取xtime */</span></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span><span class="function"><span class="title">tv_sec</span> = tk-></span>xtime_sec;</span><br><span class="line"> <span class="function"><span class="title">nsec</span> = timekeeping_get_ns(&tk-></span>tkr_mono);</span><br><span class="line"> <span class="comment">/* (2) 加上xtime和monotonic之间的差值tk->wall_to_monotonic */</span></span><br><span class="line"> <span class="function"><span class="title">tomono</span> = tk-></span>wall_to_monotonic;</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>tv_sec += tomono.tv_sec;</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>tv_nsec = <span class="number">0</span>;</span><br><span class="line"> timespec64_add_ns(ts, nsec + tomono.tv_nsec);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li><strong>raw monotonic time 的获取；</strong></li>
</ul>
<p>ktime_get_raw()通过tk->tkr_raw.base获取raw monotonic time：</p>
<figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="function">ktime_t <span class="title">ktime_get_raw</span>(<span class="params"><span class="keyword">void</span></span>)</span></span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> unsigned <span class="built_in">int</span> seq;</span><br><span class="line"> ktime_t <span class="keyword">base</span>;</span><br><span class="line"> s64 nsecs;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"> <span class="comment">/* (1) raw monotonic time = tk->tkr_raw.base */</span></span><br><span class="line"> <span class="keyword">base</span> = tk->tkr_raw.<span class="keyword">base</span>;</span><br><span class="line"> <span class="comment">/* (2) nsec需要更新最新的值：tk->tkr_raw.xtime_nsec + delta</span></span><br><span class="line"><span class="comment"> delta是距离上一次tick更新的差值 */</span></span><br><span class="line"> nsecs = timekeeping_get_ns(&tk->tkr_raw);</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ktime_add_ns(<span class="keyword">base</span>, nsecs);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>getrawmonotonic64()通过tk->raw_time获取raw monotonic time：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">getrawmonotonic64</span><span class="params">(<span class="keyword">struct</span> timespec64 *ts)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk = &tk_core.timekeeper;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timespec64</span> ts64;</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> seq;</span><br><span class="line"> s64 nsecs;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = <span class="built_in">read_seqcount_begin</span>(&tk_core.seq);</span><br><span class="line"> nsecs = <span class="built_in">timekeeping_get_ns</span>(&tk->tkr_raw);</span><br><span class="line"> ts64 = tk->raw_time;</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (<span class="built_in">read_seqcount_retry</span>(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="built_in">timespec64_add_ns</span>(&ts64, nsecs);</span><br><span class="line"> *ts = ts64;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li><strong>boot time 的获取；</strong></li>
</ul>
<p>ktime_get_boottime()使用monotonic time再加上差值timekeeper.offs_boot的方法来获取boot time：</p>
<figure class="highlight csharp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">static</span> inline ktime_t <span class="title">ktime_get_boottime</span>(<span class="params"><span class="keyword">void</span></span>)</span></span><br><span class="line">{</span><br><span class="line"> <span class="keyword">return</span> ktime_get_with_offset(TK_OFFS_BOOT);</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line"><span class="keyword">static</span> ktime_t *offsets[TK_OFFS_MAX] = {</span><br><span class="line"> [<span class="meta">TK_OFFS_REAL</span>] = &tk_core.timekeeper.offs_real,</span><br><span class="line"> [<span class="meta">TK_OFFS_BOOT</span>] = &tk_core.timekeeper.offs_boot,</span><br><span class="line"> [<span class="meta">TK_OFFS_TAI</span>] = &tk_core.timekeeper.offs_tai,</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="function">ktime_t <span class="title">ktime_get_with_offset</span>(<span class="params"><span class="built_in">enum</span> tk_offsets offs</span>)</span></span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> timekeeper *tk = &tk_core.timekeeper;</span><br><span class="line"> unsigned <span class="built_in">int</span> seq;</span><br><span class="line"> ktime_t <span class="keyword">base</span>, *offset = offsets[offs];</span><br><span class="line"> s64 nsecs;</span><br><span class="line"></span><br><span class="line"> WARN_ON(timekeeping_suspended);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqcount_begin(&tk_core.seq);</span><br><span class="line"> <span class="comment">/* (1) monotonic time = tk->tkr_mono.base，</span></span><br><span class="line"><span class="comment"> offset = timekeeper.offs_boot */</span></span><br><span class="line"> <span class="keyword">base</span> = ktime_add(tk->tkr_mono.<span class="keyword">base</span>, *offset);</span><br><span class="line"> <span class="comment">/* (2) nsec需要更新最新的值：tk->tkr_mono.xtime_nsec + delta</span></span><br><span class="line"><span class="comment"> delta是距离上一次tick更新的差值 */</span></span><br><span class="line"> nsecs = timekeeping_get_ns(&tk->tkr_mono);</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">while</span> (read_seqcount_retry(&tk_core.seq, seq));</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ktime_add_ns(<span class="keyword">base</span>, nsecs);</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h4 id="2-2-5、timekeeper-suspend"><a href="#2-2-5、timekeeper-suspend" class="headerlink" title="2.2.5、timekeeper suspend"></a>2.2.5、timekeeper suspend</h4><p>系统在进入suspend以后，clocksource不会再工作，这部分时间会计入xtime和boot time，但是不会计入monotonic time。</p>
<figure class="highlight arduino"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">timekeeping_resume</span><span class="params">(<span class="type">void</span>)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk = &tk_core.timekeeper;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">clocksource</span> *clock = tk->tkr_mono.clock;</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timespec64</span> ts_new, ts_delta;</span><br><span class="line"> <span class="type">cycle_t</span> cycle_now, cycle_delta;</span><br><span class="line"></span><br><span class="line"> sleeptime_injected = <span class="literal">false</span>;</span><br><span class="line"> <span class="built_in">read_persistent_clock64</span>(&ts_new);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">clockevents_resume</span>();</span><br><span class="line"> <span class="built_in">clocksource_resume</span>();</span><br><span class="line"></span><br><span class="line"> <span class="built_in">raw_spin_lock_irqsave</span>(&timekeeper_lock, flags);</span><br><span class="line"> <span class="built_in">write_seqcount_begin</span>(&tk_core.seq);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * After system resumes, we need to calculate the suspended time and</span></span><br><span class="line"><span class="comment"> * compensate it for the OS time. There are 3 sources that could be</span></span><br><span class="line"><span class="comment"> * used: Nonstop clocksource during suspend, persistent clock and rtc</span></span><br><span class="line"><span class="comment"> * device.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * One specific platform may have 1 or 2 or all of them, and the</span></span><br><span class="line"><span class="comment"> * preference will be:</span></span><br><span class="line"><span class="comment"> * suspend-nonstop clocksource -> persistent clock -> rtc</span></span><br><span class="line"><span class="comment"> * The less preferred source will only be tried if there is no better</span></span><br><span class="line"><span class="comment"> * usable source. The rtc part is handled separately in rtc core code.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> cycle_now = tk->tkr_mono.<span class="built_in">read</span>(clock);</span><br><span class="line"> <span class="keyword">if</span> ((clock->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) &&</span><br><span class="line"> cycle_now > tk->tkr_mono.cycle_last) {</span><br><span class="line"> u64 num, max = ULLONG_MAX;</span><br><span class="line"> u32 mult = clock->mult;</span><br><span class="line"> u32 shift = clock->shift;</span><br><span class="line"> s64 nsec = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> cycle_delta = <span class="built_in">clocksource_delta</span>(cycle_now, tk->tkr_mono.cycle_last,</span><br><span class="line"> tk->tkr_mono.mask);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * "cycle_delta * mutl" may cause 64 bits overflow, if the</span></span><br><span class="line"><span class="comment"> * suspended time is too long. In that case we need do the</span></span><br><span class="line"><span class="comment"> * 64 bits math carefully</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="built_in">do_div</span>(max, mult);</span><br><span class="line"> <span class="keyword">if</span> (cycle_delta > max) {</span><br><span class="line"> num = <span class="built_in">div64_u64</span>(cycle_delta, max);</span><br><span class="line"> nsec = (((u64) max * mult) >> shift) * num;</span><br><span class="line"> cycle_delta -= num * max;</span><br><span class="line"> }</span><br><span class="line"> nsec += ((u64) cycle_delta * mult) >> shift;</span><br><span class="line"></span><br><span class="line"> ts_delta = <span class="built_in">ns_to_timespec64</span>(nsec);</span><br><span class="line"> sleeptime_injected = <span class="literal">true</span>;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (<span class="built_in">timespec64_compare</span>(&ts_new, &timekeeping_suspend_time) > <span class="number">0</span>) {</span><br><span class="line"> ts_delta = <span class="built_in">timespec64_sub</span>(ts_new, timekeeping_suspend_time);</span><br><span class="line"> sleeptime_injected = <span class="literal">true</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (sleeptime_injected)</span><br><span class="line"> __timekeeping_inject_sleeptime(tk, &ts_delta);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Re-base the last cycle value */</span></span><br><span class="line"> tk->tkr_mono.cycle_last = cycle_now;</span><br><span class="line"> tk->tkr_raw.cycle_last = cycle_now;</span><br><span class="line"></span><br><span class="line"> tk->ntp_error = <span class="number">0</span>;</span><br><span class="line"> timekeeping_suspended = <span class="number">0</span>;</span><br><span class="line"> <span class="built_in">timekeeping_update</span>(tk, TK_MIRROR | TK_CLOCK_WAS_SET);</span><br><span class="line"> <span class="built_in">write_seqcount_end</span>(&tk_core.seq);</span><br><span class="line"> <span class="built_in">raw_spin_unlock_irqrestore</span>(&timekeeper_lock, flags);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">touch_softlockup_watchdog</span>();</span><br><span class="line"></span><br><span class="line"> <span class="built_in">tick_resume</span>();</span><br><span class="line"> <span class="built_in">hrtimers_resume</span>();</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">timekeeping_suspend</span><span class="params">(<span class="type">void</span>)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timekeeper</span> *tk = &tk_core.timekeeper;</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">timespec64</span> delta, delta_delta;</span><br><span class="line"> <span class="type">static</span> <span class="keyword">struct</span> <span class="title class_">timespec64</span> old_delta;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">read_persistent_clock64</span>(&timekeeping_suspend_time);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * On some systems the persistent_clock can not be detected at</span></span><br><span class="line"><span class="comment"> * timekeeping_init by its return value, so if we see a valid</span></span><br><span class="line"><span class="comment"> * value returned, update the persistent_clock_exists flag.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (timekeeping_suspend_time.tv_sec || timekeeping_suspend_time.tv_nsec)</span><br><span class="line"> persistent_clock_exists = <span class="literal">true</span>;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">raw_spin_lock_irqsave</span>(&timekeeper_lock, flags);</span><br><span class="line"> <span class="built_in">write_seqcount_begin</span>(&tk_core.seq);</span><br><span class="line"> <span class="built_in">timekeeping_forward_now</span>(tk);</span><br><span class="line"> timekeeping_suspended = <span class="number">1</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (persistent_clock_exists) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * To avoid drift caused by repeated suspend/resumes,</span></span><br><span class="line"><span class="comment"> * which each can add ~1 second drift error,</span></span><br><span class="line"><span class="comment"> * try to compensate so the difference in system time</span></span><br><span class="line"><span class="comment"> * and persistent_clock time stays close to constant.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> delta = <span class="built_in">timespec64_sub</span>(<span class="built_in">tk_xtime</span>(tk), timekeeping_suspend_time);</span><br><span class="line"> delta_delta = <span class="built_in">timespec64_sub</span>(delta, old_delta);</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">abs</span>(delta_delta.tv_sec) >= <span class="number">2</span>) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * if delta_delta is too large, assume time correction</span></span><br><span class="line"><span class="comment"> * has occurred and set old_delta to the current delta.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> old_delta = delta;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* Otherwise try to adjust old_system to compensate */</span></span><br><span class="line"> timekeeping_suspend_time =</span><br><span class="line"> <span class="built_in">timespec64_add</span>(timekeeping_suspend_time, delta_delta);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="built_in">timekeeping_update</span>(tk, TK_MIRROR);</span><br><span class="line"> <span class="built_in">halt_fast_timekeeper</span>(tk);</span><br><span class="line"> <span class="built_in">write_seqcount_end</span>(&tk_core.seq);</span><br><span class="line"> <span class="built_in">raw_spin_unlock_irqrestore</span>(&timekeeper_lock, flags);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">tick_suspend</span>();</span><br><span class="line"> <span class="built_in">clocksource_suspend</span>();</span><br><span class="line"> <span class="built_in">clockevents_suspend</span>();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="comment">/* sysfs resume/suspend bits for timekeeping */</span></span><br><span class="line"><span class="type">static</span> <span class="keyword">struct</span> <span class="title class_">syscore_ops</span> timekeeping_syscore_ops = {</span><br><span class="line"> .resume = timekeeping_resume,</span><br><span class="line"> .suspend = timekeeping_suspend,</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<p>和初始化一样的原因，理论上timekeeper的操作在timekeeping_resume()、timekeeping_suspend()，但是实际上在rtc的操作中执行rtc_suspend()、rtc_resume()。</p>
<figure class="highlight sas"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br></pre></td><td class="code"><pre><span class="line">static int rtc_suspend(struct device <span class="comment">*dev)</span></span><br><span class="line"><span class="comment">{</span></span><br><span class="line"><span class="comment"> struct rtc_device *rtc = to_rtc_device(dev);</span></span><br><span class="line"> struct rtc_time tm;</span><br><span class="line"> struct timespec64 delta, delta_delta;</span><br><span class="line"> int err;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (timekeeping_rtc_skipsuspend())</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (strcmp(dev_name(<span class="variable">&rtc</span>->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* snapshot the current RTC and system time at suspend*/</span></span><br><span class="line"> <span class="comment">/* (1.1) 读取suspend时候的rtc时间 */</span></span><br><span class="line"> err = rtc_read_<span class="meta">time</span>(rtc, <span class="variable">&tm</span>);</span><br><span class="line"> <span class="keyword">if</span> (err < 0) {</span><br><span class="line"> pr_debug(<span class="string">"%s: fail to read rtc time\n"</span>, dev_name(<span class="variable">&rtc</span>->dev));</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.2) 读取当前xtime */</span></span><br><span class="line"> getnstimeofday64(<span class="variable">&old_system</span>);</span><br><span class="line"> old_rtc.tv_sec = rtc_tm_to_time64(<span class="variable">&tm</span>);</span><br><span class="line"> old_rtc.tv_nsec = tm.tm_cnt<span class="comment">*(1000000000/32768);</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * To avoid drift caused by repeated suspend/resumes,</span></span><br><span class="line"><span class="comment"> * which each can add ~1 second drift error,</span></span><br><span class="line"><span class="comment"> * try to compensate so the difference in system time</span></span><br><span class="line"><span class="comment"> * and rtc time stays close to constant.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (1.3) 如果rtc时间和xtime有偏差，尝试纠正xtime */</span></span><br><span class="line"> delta = timespec64_sub(old_system, old_rtc);</span><br><span class="line"> delta_delta = timespec64_sub(delta, old_delta);</span><br><span class="line"> <span class="keyword">if</span> (delta_delta.tv_sec < -2 || delta_delta.tv_sec >= 2) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * if delta_delta is too large, assume time correction</span></span><br><span class="line"><span class="comment"> * has occured and set old_delta to the current delta.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> old_delta = delta;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* Otherwise try to adjust old_system to compensate */</span></span><br><span class="line"> old_system = timespec64_sub(old_system, delta_delta);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">static int rtc_resume(struct device <span class="comment">*dev)</span></span><br><span class="line"><span class="comment">{</span></span><br><span class="line"><span class="comment"> struct rtc_device *rtc = to_rtc_device(dev);</span></span><br><span class="line"> struct rtc_time tm;</span><br><span class="line"> struct timespec64 new_system, new_rtc;</span><br><span class="line"> struct timespec64 sleep_time;</span><br><span class="line"> int err;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (timekeeping_rtc_skipresume())</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"></span><br><span class="line"> rtc_hctosys_ret = -ENODEV;</span><br><span class="line"> <span class="keyword">if</span> (strcmp(dev_name(<span class="variable">&rtc</span>->dev), CONFIG_RTC_HCTOSYS_DEVICE) != 0)</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* snapshot the current rtc and system time at resume */</span></span><br><span class="line"> <span class="comment">/* (2.1) 读取resume后的rtc时间和xtime */</span></span><br><span class="line"> getnstimeofday64(<span class="variable">&new_system</span>);</span><br><span class="line"> err = rtc_read_<span class="meta">time</span>(rtc, <span class="variable">&tm</span>);</span><br><span class="line"> <span class="keyword">if</span> (err < 0) {</span><br><span class="line"> pr_debug(<span class="string">"%s: fail to read rtc time\n"</span>, dev_name(<span class="variable">&rtc</span>->dev));</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> new_rtc.tv_sec = rtc_tm_to_time64(<span class="variable">&tm</span>);</span><br><span class="line"> new_rtc.tv_nsec = tm.tm_cnt<span class="comment">*(1000000000/32768);</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (new_rtc.tv_sec < old_rtc.tv_sec) {</span><br><span class="line"> pr_debug(<span class="string">"%s: time travel!\n"</span>, dev_name(<span class="variable">&rtc</span>->dev));</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* calculate the RTC time delta (sleep time)*/</span></span><br><span class="line"> <span class="comment">/* (2.2) 计算suspend和resume之间rtc的差值 */</span></span><br><span class="line"> sleep_time = timespec64_sub(new_rtc, old_rtc);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Since these RTC suspend/resume handlers are not called</span></span><br><span class="line"><span class="comment"> * at the very end of suspend or the start of resume,</span></span><br><span class="line"><span class="comment"> * some run-time may pass on either sides of the sleep time</span></span><br><span class="line"><span class="comment"> * so subtract kernel run-time between rtc_suspend to rtc_resume</span></span><br><span class="line"><span class="comment"> * to keep things accurate.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.3) 使用上一步的差值，再减去，suspend和resume之间xtime的差值</span></span><br><span class="line"><span class="comment"> 得到实际的sleep时间*/</span></span><br><span class="line"> sleep_time = timespec64_sub(sleep_time,</span><br><span class="line"> timespec64_sub(new_system, old_system));</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (sleep_time.tv_sec >= 0)</span><br><span class="line"> <span class="comment">/* (2.4) 将计算得到的sleep时间，加入到timekeeper中 */</span></span><br><span class="line"> timekeeping_inject_sleeptime64(<span class="variable">&sleep_time</span>);</span><br><span class="line"> rtc_hctosys_ret = 0;</span><br><span class="line"> <span class="keyword">return</span> 0;</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">void timekeeping_inject_sleeptime64(struct timespec64 <span class="comment">*delta)</span></span><br><span class="line"><span class="comment">{</span></span><br><span class="line"><span class="comment"> struct timekeeper *tk = &tk_core.timekeeper;</span></span><br><span class="line"> unsigned long flags;</span><br><span class="line"></span><br><span class="line"> raw_spin_lock_irqsave(<span class="variable">&timekeeper_lock</span>, flags);</span><br><span class="line"> write_seqcount_begi<span class="meta">n</span>(<span class="variable">&tk_core.</span>seq);</span><br><span class="line"></span><br><span class="line"> timekeeping_forward_now(tk);</span><br><span class="line"></span><br><span class="line"> __timekeeping_inject_sleep<span class="meta">time</span>(tk, delta);</span><br><span class="line"></span><br><span class="line"> timekeeping_up<span class="meta">date</span>(tk, TK_CLEAR_NTP | TK_MIRROR | TK_CLOCK_WAS_SET);</span><br><span class="line"></span><br><span class="line"> write_seqcount_end(<span class="variable">&tk_core.</span>seq);</span><br><span class="line"> raw_spin_unlock_irqrestore(<span class="variable">&timekeeper_lock</span>, flags);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* signal hrtimers about time change */</span></span><br><span class="line"> clock_was_set();</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line">static void __timekeeping_inject_sleep<span class="meta">time</span>(struct timekeeper <span class="comment">*tk,</span></span><br><span class="line"><span class="comment"> struct timespec64 *delta)</span></span><br><span class="line"><span class="comment">{</span></span><br><span class="line"><span class="comment"> if (!timespec64_valid_strict(delta)) {</span></span><br><span class="line"><span class="comment"> printk_deferred(KERN_WARNING</span></span><br><span class="line"><span class="comment"> "__timekeeping_inject_sleeptime: Invalid "</span></span><br><span class="line"><span class="comment"> "sleep delta value!\n");</span></span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">/* (2.4.1) 更新xtime */</span></span><br><span class="line"> tk_xtime_add(tk, delta);</span><br><span class="line"> <span class="comment">/* (2.4.2) 更新tk->wall_to_monotonic、tk->offs_real */</span></span><br><span class="line"> tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, <span class="comment">*delta));</span></span><br><span class="line"> <span class="comment">/* (2.4.3) 更新tk->offs_boot */</span></span><br><span class="line"> tk_update_sleep_<span class="meta">time</span>(tk, timespec64_to_k<span class="meta">time</span>(<span class="comment">*delta));</span></span><br><span class="line"> tk_debug_account_sleep_<span class="meta">time</span>(delta);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="3、clock-event"><a href="#3、clock-event" class="headerlink" title="3、clock_event"></a>3、clock_event</h2><p><img src="clockevent.png" alt="image"></p>
<p>clock_event其实就是对local timer的使用，每个cpu对应一个本地local timer。global timer启动后不需要主动做任何事情，只需要等待timekepper的读取就可以了。而local timer需要触发中断，它的主要价值就体现在定时中断处理了，中断的时间可以是固定的(period mode)也或者是不固定的(oneshot mode)。</p>
<h3 id="3-1、clock-event的注册"><a href="#3-1、clock-event的注册" class="headerlink" title="3.1、clock_event的注册"></a>3.1、clock_event的注册</h3><h4 id="3-1-1、exynos-clock-event的注册"><a href="#3-1-1、exynos-clock-event的注册" class="headerlink" title="3.1.1、exynos clock_event的注册"></a>3.1.1、exynos clock_event的注册</h4><p>exynos clock_event的注册分为两部分：</p>
<ul>
<li>第一部分：localtimer中断的注册：</li>
</ul>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">static</span> <span class="type">void</span> __init <span class="title">exynos4_timer_resources</span><span class="params">(<span class="keyword">struct</span> device_node *np, <span class="type">void</span> __iomem *base)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="type">int</span> err, cpu;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">mct_clock_event_device</span> *mevt = <span class="built_in">this_cpu_ptr</span>(&percpu_mct_tick);</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">clk</span> *mct_clk, *tick_clk;</span><br><span class="line"></span><br><span class="line"> tick_clk = np ? <span class="built_in">of_clk_get_by_name</span>(np, <span class="string">"fin_pll"</span>) :</span><br><span class="line"> <span class="built_in">clk_get</span>(<span class="literal">NULL</span>, <span class="string">"fin_pll"</span>);</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">IS_ERR</span>(tick_clk))</span><br><span class="line"> <span class="built_in">panic</span>(<span class="string">"%s: unable to determine tick clock rate\n"</span>, __func__);</span><br><span class="line"> clk_rate = <span class="built_in">clk_get_rate</span>(tick_clk);</span><br><span class="line"></span><br><span class="line"> mct_clk = np ? <span class="built_in">of_clk_get_by_name</span>(np, <span class="string">"mct"</span>) : <span class="built_in">clk_get</span>(<span class="literal">NULL</span>, <span class="string">"mct"</span>);</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">IS_ERR</span>(mct_clk))</span><br><span class="line"> <span class="built_in">panic</span>(<span class="string">"%s: unable to retrieve mct clock instance\n"</span>, __func__);</span><br><span class="line"> <span class="built_in">clk_prepare_enable</span>(mct_clk);</span><br><span class="line"></span><br><span class="line"> reg_base = base;</span><br><span class="line"> <span class="keyword">if</span> (!reg_base)</span><br><span class="line"> <span class="built_in">panic</span>(<span class="string">"%s: unable to ioremap mct address space\n"</span>, __func__);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (mct_int_type == MCT_INT_PPI) {</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 大部分的localtimer是PPI模式，</span></span><br><span class="line"><span class="comment"> 注册中断处理函数：exynos4_mct_tick_isr() */</span></span><br><span class="line"> err = <span class="built_in">request_percpu_irq</span>(mct_irqs[MCT_L0_IRQ],</span><br><span class="line"> exynos4_mct_tick_isr, <span class="string">"MCT"</span>,</span><br><span class="line"> &percpu_mct_tick);</span><br><span class="line"> <span class="built_in">WARN</span>(err, <span class="string">"MCT: can't request IRQ %d (%d)\n"</span>,</span><br><span class="line"> mct_irqs[MCT_L0_IRQ], err);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> for_each_possible_cpu(cpu) {</span><br><span class="line"> <span class="type">int</span> mct_irq = mct_irqs[MCT_L0_IRQ + cpu];</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">mct_clock_event_device</span> *pcpu_mevt =</span><br><span class="line"> <span class="built_in">per_cpu_ptr</span>(&percpu_mct_tick, cpu);</span><br><span class="line"></span><br><span class="line"> pcpu_mevt->evt.irq = <span class="number">-1</span>;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">irq_set_status_flags</span>(mct_irq, IRQ_NOAUTOEN);</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">request_irq</span>(mct_irq,</span><br><span class="line"> exynos4_mct_tick_isr,</span><br><span class="line"> IRQF_TIMER | IRQF_NOBALANCING,</span><br><span class="line"> pcpu_mevt->name, pcpu_mevt)) {</span><br><span class="line"> <span class="built_in">pr_err</span>(<span class="string">"exynos-mct: cannot register IRQ (cpu%d)\n"</span>,</span><br><span class="line"> cpu);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">continue</span>;</span><br><span class="line"> }</span><br><span class="line"> pcpu_mevt->evt.irq = mct_irq;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2) 注册cpu hotplug的notifier，</span></span><br><span class="line"><span class="comment"> 在其他cpu up时调用exynos4_local_timer_setup()注册clock_event */</span></span><br><span class="line"> err = <span class="built_in">register_cpu_notifier</span>(&exynos4_mct_cpu_nb);</span><br><span class="line"> <span class="keyword">if</span> (err)</span><br><span class="line"> <span class="keyword">goto</span> out_irq;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Immediately configure the timer on the boot CPU */</span></span><br><span class="line"> <span class="comment">/* (3) 注册本cpu的clock_event */</span></span><br><span class="line"> <span class="built_in">exynos4_local_timer_setup</span>(mevt);</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"></span><br><span class="line">out_irq:</span><br><span class="line"> <span class="built_in">free_percpu_irq</span>(mct_irqs[MCT_L0_IRQ], &percpu_mct_tick);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">static</span> <span class="type">irqreturn_t</span> <span class="title">exynos4_mct_tick_isr</span><span class="params">(<span class="type">int</span> irq, <span class="type">void</span> *dev_id)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">mct_clock_event_device</span> *mevt = dev_id;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">clock_event_device</span> *evt = &mevt->evt;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">exynos4_mct_tick_clear</span>(mevt);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (4) localtimer中断处理函数是固定的也是非常简单的，</span></span><br><span class="line"><span class="comment"> 调用本cpu clock_event_device的handler函数：evt->event_handler(evt) */</span></span><br><span class="line"> evt-><span class="built_in">event_handler</span>(evt);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> IRQ_HANDLED;</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<ul>
<li>第二部分：clock_event_device注册：</li>
</ul>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br></pre></td><td class="code"><pre><span class="line">static int exynos4_local_timer_setup(struct mct_clock_event_device *mevt)</span><br><span class="line">{</span><br><span class="line"> <span class="function"><span class="title">struct</span> clock_event_device *evt = &mevt-></span>evt;</span><br><span class="line"> unsigned int cpu = smp_processor_id();</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">mevt</span>-></span>base = EXYNOS4_MCT_L_BASE(cpu);</span><br><span class="line"> <span class="function"><span class="title">snprintf</span>(mevt-></span><span class="function"><span class="title">name</span>, sizeof(mevt-></span><span class="keyword">name</span>), <span class="string">"mct_tick%d"</span>, cpu);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 初始化clock_event_device */</span></span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span><span class="function"><span class="title">name</span> = mevt-></span><span class="keyword">name</span>;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>cpumask = cpumask_of(cpu); <span class="comment">// 本clock_event_device只服务于一个cpu</span></span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>set_next_event = exynos4_tick_set_next_event;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>set_state_periodic = set_state_periodic;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>set_state_shutdown = set_state_shutdown;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>set_state_oneshot = set_state_shutdown;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>tick_resume = set_state_shutdown;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;</span><br><span class="line"> <span class="function"><span class="title">evt</span>-></span>rating = <span class="number">450</span>;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">exynos4_mct_write</span>(TICK_BASE_CNT, mevt-></span>base + MCT_L_TCNTB_OFFSET);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (mct_int_type == MCT_INT_SPI) {</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (evt-></span>irq == -<span class="number">1</span>)</span><br><span class="line"> return -EIO;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">irq_force_affinity</span>(evt-></span>irq, cpumask_of(cpu));</span><br><span class="line"> <span class="function"><span class="title">enable_irq</span>(evt-></span>irq);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> enable_percpu_irq(mct_irqs[MCT_L0_IRQ], <span class="number">0</span>);</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">/* (2) 配置并注册clockevent */</span></span><br><span class="line"> clockevents_config_and_register(evt, clk_rate / (TICK_BASE_CNT + <span class="number">1</span>),</span><br><span class="line"> <span class="number">0</span>xf, <span class="number">0</span>x7fffffff);</span><br><span class="line"></span><br><span class="line"> return <span class="number">0</span>;</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h4 id="3-1-2、clock-event-device的注册"><a href="#3-1-2、clock-event-device的注册" class="headerlink" title="3.1.2、clock_event_device的注册"></a>3.1.2、clock_event_device的注册</h4><p>我们来分析一下clock_event_device的注册过程。</p>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br><span class="line">185</span><br><span class="line">186</span><br><span class="line">187</span><br><span class="line">188</span><br><span class="line">189</span><br></pre></td><td class="code"><pre><span class="line">void clockevents_config_and_register(struct clock_event_device *dev,</span><br><span class="line"> u32 freq, unsigned long min_delta,</span><br><span class="line"> unsigned long max_delta)</span><br><span class="line">{</span><br><span class="line"> <span class="function"><span class="title">dev</span>-></span>min_delta_ticks = min_delta; <span class="comment">// localtimer可配置的最小定时值</span></span><br><span class="line"> <span class="function"><span class="title">dev</span>-></span>max_delta_ticks = max_delta; <span class="comment">// localtimer可配置的最大定时值，</span></span><br><span class="line"> <span class="comment">// 比如exynos是31bit的localtimer，最大值就是0x7fffffff</span></span><br><span class="line"> <span class="comment">/* (1) 根据localtimer的freq，计算clock_event_device对应的mult、shift，</span></span><br><span class="line"><span class="comment"> mult、shift的作用是用来做ns到localtimer cycle之间的转换，</span></span><br><span class="line"><span class="comment"> 与之相反的是，在clocksource中mult、shift用来转换localtimer cycle到ns */</span></span><br><span class="line"> clockevents_config(dev, freq);</span><br><span class="line"> <span class="comment">/* (2) 继续注册clock_event_device */</span></span><br><span class="line"> clockevents_register_device(dev);</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">void clockevents_config(struct clock_event_device *dev, u32 freq)</span><br><span class="line">{</span><br><span class="line"> u64 sec;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.1) 如果不支持oneshot模式，只是period模式，</span></span><br><span class="line"><span class="comment"> 定时周期是固定的，不需要动态计算ns到cycle的转换 */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (!(dev-></span>features & CLOCK_EVT_FEAT_ONESHOT))</span><br><span class="line"> return;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Calculate the maximum number of seconds we can sleep. Limit</span></span><br><span class="line"><span class="comment"> * to 10 minutes for hardware which can program more than</span></span><br><span class="line"><span class="comment"> * 32bit ticks so we still get reasonable conversion values.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">sec</span> = dev-></span>max_delta_ticks;</span><br><span class="line"> do_div(sec, freq);</span><br><span class="line"> <span class="keyword">if</span> (!sec)</span><br><span class="line"> sec = <span class="number">1</span>;</span><br><span class="line"> <span class="function"><span class="title">else</span> <span class="keyword">if</span> (sec > 600 && dev-></span>max_delta_ticks > UINT_MAX)</span><br><span class="line"> sec = <span class="number">600</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.2) 根据localtimer的freq，计算clock_event_device对应的mult、shift */</span></span><br><span class="line"> clockevents_calc_mult_shift(dev, freq, sec);</span><br><span class="line"> <span class="comment">/* (1.3) 转换min、max的cycle到ns */</span></span><br><span class="line"> <span class="function"><span class="title">dev</span>-></span><span class="function"><span class="title">min_delta_ns</span> = cev_delta2ns(dev-></span>min_delta_ticks, dev, <span class="literal">false</span>);</span><br><span class="line"> <span class="function"><span class="title">dev</span>-></span><span class="function"><span class="title">max_delta_ns</span> = cev_delta2ns(dev-></span>max_delta_ticks, dev, <span class="literal">true</span>);</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">void clockevents_register_device(struct clock_event_device *dev)</span><br><span class="line">{</span><br><span class="line"> unsigned long flags;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Initialize state to DETACHED */</span></span><br><span class="line"> clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (!dev-></span>cpumask) {</span><br><span class="line"> WARN_ON(num_possible_cpus() > <span class="number">1</span>);</span><br><span class="line"> <span class="function"><span class="title">dev</span>-></span>cpumask = cpumask_of(smp_processor_id());</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> raw_spin_lock_irqsave(&clockevents_lock, flags);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.1) 将clock_event_device加入到全局链表clockevent_devices中 */</span></span><br><span class="line"> <span class="function"><span class="title">list_add</span>(&dev-></span>list, &clockevent_devices);</span><br><span class="line"> <span class="comment">/* (2.2) 继续尝试向本cpu的tick_device中注册clock_event_device */</span></span><br><span class="line"> tick_check_new_device(dev);</span><br><span class="line"> clockevents_notify_released();</span><br><span class="line"></span><br><span class="line"> raw_spin_unlock_irqrestore(&clockevents_lock, flags);</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line">void tick_check_new_device(struct clock_event_device *newdev)</span><br><span class="line">{</span><br><span class="line"> struct clock_event_device *curdev;</span><br><span class="line"> struct tick_device *td;</span><br><span class="line"> int cpu;</span><br><span class="line"></span><br><span class="line"> cpu = smp_processor_id();</span><br><span class="line"> td = &per_cpu(tick_cpu_device, cpu);</span><br><span class="line"> <span class="function"><span class="title">curdev</span> = td-></span>evtdev;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* cpu local device ? */</span></span><br><span class="line"> <span class="comment">/* (2.2.1) 新的clock_event_device是否支持本cpu？ */</span></span><br><span class="line"> <span class="keyword">if</span> (!tick_check_percpu(curdev, newdev, cpu))</span><br><span class="line"> goto out_bc;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Preference decision */</span></span><br><span class="line"> <span class="comment">/* (2.2.2) 新的clock_event_device是否比当前clock_event_device更适合？</span></span><br><span class="line"><span class="comment"> 1.如果curdev已经是oneshot模式，而newdev不支持oneshot，则切换</span></span><br><span class="line"><span class="comment"> 2.newdev的精度要大于curdev，精度 = dev->rating */</span></span><br><span class="line"> <span class="keyword">if</span> (!tick_check_preferred(curdev, newdev))</span><br><span class="line"> goto out_bc;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (!try_module_get(newdev-></span>owner))</span><br><span class="line"> return;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Replace the eventually existing device by the new</span></span><br><span class="line"><span class="comment"> * device. If the current device is the broadcast device, do</span></span><br><span class="line"><span class="comment"> * not give it back to the clockevents layer !</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (tick_is_broadcast_device(curdev)) {</span><br><span class="line"> clockevents_shutdown(curdev);</span><br><span class="line"> curdev = NULL;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">/* (2.2.3) 关闭curdev、newdev */</span></span><br><span class="line"> clockevents_exchange_device(curdev, newdev);</span><br><span class="line"> <span class="comment">/* (2.2.4) 继续clock_event_device注册 */</span></span><br><span class="line"> tick_setup_device(td, newdev, cpu, cpumask_of(cpu));</span><br><span class="line"> <span class="function"><span class="title">if</span> (newdev-></span>features & CLOCK_EVT_FEAT_ONESHOT)</span><br><span class="line"> tick_oneshot_notify();</span><br><span class="line"> return;</span><br><span class="line"></span><br><span class="line">out_bc:</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Can the new device be used as a broadcast device ?</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.2.5) 如果newdev不适合注册成本cpu的td->evtdev,</span></span><br><span class="line"><span class="comment"> 尝试将其注册成broadcast clockevent */</span></span><br><span class="line"> tick_install_broadcast_device(newdev);</span><br><span class="line">}</span><br><span class="line">|||→</span><br><span class="line">static void tick_setup_device(struct tick_device *td,</span><br><span class="line"> struct clock_event_device *newdev, int cpu,</span><br><span class="line"> const struct cpumask *cpumask)</span><br><span class="line">{</span><br><span class="line"> ktime_t next_event;</span><br><span class="line"> void (*handler)(struct clock_event_device *) = NULL;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * First device setup ?</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (!td-></span>evtdev) {</span><br><span class="line"> <span class="comment">/* (2.2.4.1) 如果是tick_do_timer_cpu没有被设置，且没有使能tick_nohz_full_cpu</span></span><br><span class="line"><span class="comment"> 把tick_do_timer_cpu设置成本cpu，</span></span><br><span class="line"><span class="comment"> tick_do_timer_cpu负责在tick中update jiffies、update_wall_time */</span></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * If no cpu took the do_timer update, assign it to</span></span><br><span class="line"><span class="comment"> * this cpu:</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {</span><br><span class="line"> <span class="keyword">if</span> (!tick_nohz_full_cpu(cpu))</span><br><span class="line"> tick_do_timer_cpu = cpu;</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> tick_do_timer_cpu = TICK_DO_TIMER_NONE;</span><br><span class="line"> tick_next_period = ktime_get();</span><br><span class="line"> tick_period = ktime_set(<span class="number">0</span>, NSEC_PER_SEC / HZ);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Startup in periodic mode first.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.2.4.2) 如果tick_device是第一次设置clock_event_device,</span></span><br><span class="line"><span class="comment"> 把tick_device设置成period模式 */</span></span><br><span class="line"> <span class="function"><span class="title">td</span>-></span>mode = TICKDEV_MODE_PERIODIC;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* (2.2.4.3) 如果tick_device不是第一次设置clock_event_device,</span></span><br><span class="line"><span class="comment"> 备份原clock_event_deviced的event_handler和next_event */</span></span><br><span class="line"> <span class="function"><span class="title">handler</span> = td-></span><span class="function"><span class="title">evtdev</span>-></span>event_handler;</span><br><span class="line"> <span class="function"><span class="title">next_event</span> = td-></span><span class="function"><span class="title">evtdev</span>-></span>next_event;</span><br><span class="line"> <span class="function"><span class="title">td</span>-></span><span class="function"><span class="title">evtdev</span>-></span>event_handler = clockevents_handle_noop;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.2.4.4) 更新tick_device->evtdev到new clock_event_deviced */</span></span><br><span class="line"> <span class="function"><span class="title">td</span>-></span>evtdev = newdev;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * When the device is not per cpu, pin the interrupt to the</span></span><br><span class="line"><span class="comment"> * current cpu:</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (!cpumask_equal(newdev-></span>cpumask, cpumask))</span><br><span class="line"> <span class="function"><span class="title">irq_set_affinity</span>(newdev-></span>irq, cpumask);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * When global broadcasting is active, check if the current</span></span><br><span class="line"><span class="comment"> * device is registered as a placeholder for broadcast mode.</span></span><br><span class="line"><span class="comment"> * This allows us to handle this x86 misfeature in a generic</span></span><br><span class="line"><span class="comment"> * way. This function also returns !=0 when we keep the</span></span><br><span class="line"><span class="comment"> * current active broadcast state for this CPU.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.2.4.5) 如果全局的brodcast clockevent服务已经启动，</span></span><br><span class="line"><span class="comment"> 本cpu的clockevent注册需要向brodcas服务，</span></span><br><span class="line"><span class="comment"> 这是为了解决x86的一个失误(misfeature)，其他架构不需要？ */</span></span><br><span class="line"> <span class="keyword">if</span> (tick_device_uses_broadcast(newdev, cpu))</span><br><span class="line"> return;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.2.4.6) 根据td->mode安装clock_event_deviced的event_handler,并启动 */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (td-></span>mode == TICKDEV_MODE_PERIODIC)</span><br><span class="line"> <span class="comment">/* (2.2.4.7) period模式 */</span></span><br><span class="line"> tick_setup_periodic(newdev, <span class="number">0</span>);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="comment">/* (2.2.4.8) oneshot模式 */</span></span><br><span class="line"> tick_setup_oneshot(newdev, handler, next_event);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="3-2、tick-device的period-mode"><a href="#3-2、tick-device的period-mode" class="headerlink" title="3.2、tick_device的period mode"></a>3.2、tick_device的period mode</h3><p>接上节，在cpu第一次注册clock_event_deviced的时候，td->mode默认被设置成period模式。event_handler会被初始化成tick_handle_periodic：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">tick_setup_periodic</span><span class="params">(<span class="keyword">struct</span> clock_event_device *dev, <span class="type">int</span> broadcast)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="comment">/* (1) 设置period模式下的event_handler */</span></span><br><span class="line"> <span class="built_in">tick_set_periodic_handler</span>(dev, broadcast);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Broadcast setup ? */</span></span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">tick_device_is_functional</span>(dev))</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2) 如果dev支持period模式，则硬件上启动period模式:</span></span><br><span class="line"><span class="comment"> tick_device->mode = TICKDEV_MODE_PERIODIC</span></span><br><span class="line"><span class="comment"> clock_event_device->state_use_accessors = CLOCK_EVT_STATE_PERIODIC */</span></span><br><span class="line"> <span class="keyword">if</span> ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&</span><br><span class="line"> !<span class="built_in">tick_broadcast_oneshot_active</span>()) {</span><br><span class="line"> <span class="built_in">clockevents_switch_state</span>(dev, CLOCK_EVT_STATE_PERIODIC);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> seq;</span><br><span class="line"> <span class="type">ktime_t</span> next;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = <span class="built_in">read_seqbegin</span>(&jiffies_lock);</span><br><span class="line"> next = tick_next_period;</span><br><span class="line"> } <span class="keyword">while</span> (<span class="built_in">read_seqretry</span>(&jiffies_lock, seq));</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (3) 如果dev不支持period模式只支持oneshot模式，则硬件上启动one shot模式，</span></span><br><span class="line"><span class="comment"> 使用oneshot模式来模拟period模式：</span></span><br><span class="line"><span class="comment"> tick_device->mode = TICKDEV_MODE_PERIODIC</span></span><br><span class="line"><span class="comment"> clock_event_device->state_use_accessors = CLOCK_EVT_STATE_ONESHOT */</span></span><br><span class="line"> <span class="built_in">clockevents_switch_state</span>(dev, CLOCK_EVT_STATE_ONESHOT);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> (;;) {</span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">clockevents_program_event</span>(dev, next, <span class="literal">false</span>))</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> next = <span class="built_in">ktime_add</span>(next, tick_period);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">tick_set_periodic_handler</span><span class="params">(<span class="keyword">struct</span> clock_event_device *dev, <span class="type">int</span> broadcast)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">if</span> (!broadcast)</span><br><span class="line"> <span class="comment">/* (1.1) 设置period模式下的event_handler */</span></span><br><span class="line"> dev->event_handler = tick_handle_periodic;</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> dev->event_handler = tick_handle_periodic_broadcast;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>仔细分析一下tick_handle_periodic：</p>
<figure class="highlight lisp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br></pre></td><td class="code"><pre><span class="line">void tick_handle_periodic(<span class="name">struct</span> clock_event_device *dev)</span><br><span class="line">{</span><br><span class="line"> int cpu = smp_processor_id();</span><br><span class="line"> ktime_t next = dev->next_event;</span><br><span class="line"></span><br><span class="line"> /* (<span class="number">1</span>) 周期性的tick任务 */</span><br><span class="line"> tick_periodic(cpu);</span><br><span class="line"></span><br><span class="line">#if defined(CONFIG_HIGH_RES_TIMERS) || defined(CONFIG_NO_HZ_COMMON)</span><br><span class="line"> /*</span><br><span class="line"> * The cpu might have transitioned to HIGHRES or NOHZ mode via</span><br><span class="line"> * update_process_times() -> run_local_timers() -></span><br><span class="line"> * hrtimer_run_queues().</span><br><span class="line"> */</span><br><span class="line"> if (<span class="name">dev->event_handler</span> != tick_handle_periodic)</span><br><span class="line"> return<span class="comment">;</span></span><br><span class="line">#endif</span><br><span class="line"></span><br><span class="line"> if (!clockevent_state_oneshot(<span class="name">dev</span>))</span><br><span class="line"> return<span class="comment">;</span></span><br><span class="line"> /* (<span class="number">2</span>) 如果tick_device是period mode，而clockevent是oneshot模式,</span><br><span class="line"> 编程oneshot模式clockevent在下一周期触发：</span><br><span class="line"> tick_device->mode = TICKDEV_MODE_PERIODIC</span><br><span class="line"> clock_event_device->state_use_accessors = CLOCK_EVT_STATE_ONESHOT */</span><br><span class="line"> for (;;) {</span><br><span class="line"> /*</span><br><span class="line"> * Setup the next period for devices, which do not have</span><br><span class="line"> * periodic mode:</span><br><span class="line"> */</span><br><span class="line"> next = ktime_add(next, tick_period);</span><br><span class="line"></span><br><span class="line"> if (!clockevents_program_event(dev, next, false))</span><br><span class="line"> return;</span><br><span class="line"> /*</span><br><span class="line"> * Have to be careful here. If we're in oneshot mode,</span><br><span class="line"> * before we call tick_periodic() in a loop, we need</span><br><span class="line"> * to be sure we're using a real hardware clocksource.</span><br><span class="line"> * Otherwise we could get trapped in an infinite</span><br><span class="line"> * loop, as the tick_periodic() increments jiffies,</span><br><span class="line"> * which then will increment time, possibly causing</span><br><span class="line"> * the loop to trigger again and again.</span><br><span class="line"> */</span><br><span class="line"> if (<span class="name">timekeeping_valid_for_hres</span>())</span><br><span class="line"> tick_periodic(<span class="name">cpu</span>)<span class="comment">;</span></span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">static void tick_periodic(<span class="name">int</span> cpu)</span><br><span class="line">{</span><br><span class="line"> /* (<span class="number">1.1</span>) 如果本cpu是tick_do_timer_cpu，更新全局时间戳类型的任务，</span><br><span class="line"> 包括update jiffies、update_wall_time */</span><br><span class="line"> if (tick_do_timer_cpu == cpu) {</span><br><span class="line"> write_seqlock(&jiffies_lock);</span><br><span class="line"></span><br><span class="line"> /* Keep track of the next tick event */</span><br><span class="line"> tick_next_period = ktime_add(tick_next_period, tick_period);</span><br><span class="line"></span><br><span class="line"> /* (<span class="number">1.1</span>.<span class="number">1</span>) 更新jiffies */</span><br><span class="line"> do_timer(1);</span><br><span class="line"> write_sequnlock(&jiffies_lock);</span><br><span class="line"> /* (<span class="number">1.1</span>.<span class="number">2</span>) 读取clocksource来更新timekeeper */</span><br><span class="line"> update_wall_time();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> /* (<span class="number">1.2</span>) 运行软件timer(<span class="name">run_local_timers</span>())和运行调度tick任务(<span class="name">scheduler_tick</span>()) */</span><br><span class="line"> update_process_times(user_mode(get_irq_regs()));</span><br><span class="line"> profile_tick(CPU_PROFILING);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="3-3、运行Mode"><a href="#3-3、运行Mode" class="headerlink" title="3.3、运行Mode"></a>3.3、运行Mode</h3><p>关于mode，有几个结构涉及到：tick_device、clock_event_device、tick_sched、hrtimer_cpu_base、。组合起来有以下几种情况：</p>
<p><img src="clockevent_mode.png" alt="image"></p>
<p>其实归结起来就3种mode：NOHZ_MODE_INACTIVE、NOHZ_MODE_LOWRES、NOHZ_MODE_HIGHRES。下面来逐个解析一下。</p>
<h4 id="3-3-1、NOHZ-MODE-INACTIVE"><a href="#3-3-1、NOHZ-MODE-INACTIVE" class="headerlink" title="3.3.1、NOHZ_MODE_INACTIVE"></a>3.3.1、NOHZ_MODE_INACTIVE</h4><p>NOHZ_MODE_INACTIVE就是系统初始化时的状态：“td=period模式, dev=period/oneshot模式, hrtimer=low res, noHz=dis”。</p>
<p><img src="clockevent_NOHZ_MODE_INACTIVE.png" alt="image"></p>
<p>NOHZ_MODE_INACTIVE模式：</p>
<ul>
<li>tick_device工作在period模式，HW local timer工作在period/oneshot模式；</li>
<li>noHZ没有使能，进入idle会被tick timer中断打断；</li>
<li>hrtimer工作在低精度模式，和低精度定时器(SW local timer)的精度一样，都是基于tick的；</li>
</ul>
<h4 id="3-3-2、NOHZ-MODE-LOWRES"><a href="#3-3-2、NOHZ-MODE-LOWRES" class="headerlink" title="3.3.2、NOHZ_MODE_LOWRES"></a>3.3.2、NOHZ_MODE_LOWRES</h4><p>在系统的运行过程中系统尝试进入精度更高的模式，如果noHZ可以使能，但是hrtimer高精度不能使能，即进入NOHZ_MODE_LOWRES模式：“td=period模式, dev=oneshot模式, hrtimer=low res, noHz=en”。</p>
<p><img src="clockevent_NOHZ_MODE_LOWRES.png" alt="image"></p>
<p>NOHZ_MODE_LOWRES模式：</p>
<ul>
<li>tick_device工作在oneshot模式，HW local timer工作在oneshot模式；</li>
<li>noHZ使能，进入idle不会被tick timer中断打断；</li>
<li>hrtimer工作在低精度模式，和低精度定时器(SW local timer)的精度一样，都是基于tick的；</li>
</ul>
<p>为了支持noHZ，tick_device必须切换成oneshot模式，在进入idle时停掉tick timer(tick_nohz_idle_enter() -> __tick_nohz_idle_enter() -> tick_nohz_stop_sched_tick())，在离开idle时恢复tick timer(tick_nohz_idle_exit() -> tick_nohz_restart_sched_tick())，这样idle过程就不会被tick中断。就实现了noHZ模式(tickless)。</p>
<p>NOHZ_MODE_LOWRES模式下，没有进入idle时tick_device还是以固定周期工作的：</p>
<figure class="highlight rust"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">static</span> void <span class="title function_ invoke__">tick_nohz_handler</span>(<span class="keyword">struct</span> <span class="title class_">clock_event_device</span> *dev)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">tick_sched</span> *ts = <span class="title function_ invoke__">this_cpu_ptr</span>(&tick_cpu_sched);</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">pt_regs</span> *regs = <span class="title function_ invoke__">get_irq_regs</span>();</span><br><span class="line"> ktime_t now = <span class="title function_ invoke__">ktime_get</span>();</span><br><span class="line"></span><br><span class="line"> dev<span class="punctuation">-></span>next_event.tv64 = KTIME_MAX;</span><br><span class="line"></span><br><span class="line"> <span class="title function_ invoke__">tick_sched_do_timer</span>(now);</span><br><span class="line"> <span class="title function_ invoke__">tick_sched_handle</span>(ts, regs);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* No need to reprogram if we are running tickless */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="title function_ invoke__">unlikely</span>(ts<span class="punctuation">-></span>tick_stopped))</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) HW local timer还是以固定周期发生中断 */</span></span><br><span class="line"> <span class="title function_ invoke__">hrtimer_forward</span>(&ts<span class="punctuation">-></span>sched_timer, now, tick_period);</span><br><span class="line"> <span class="title function_ invoke__">tick_program_event</span>(<span class="title function_ invoke__">hrtimer_get_expires</span>(&ts<span class="punctuation">-></span>sched_timer), <span class="number">1</span>);</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h4 id="3-3-3、NOHZ-MODE-HIGHRES"><a href="#3-3-3、NOHZ-MODE-HIGHRES" class="headerlink" title="3.3.3、NOHZ_MODE_HIGHRES"></a>3.3.3、NOHZ_MODE_HIGHRES</h4><p>在系统的运行过程中系统尝试进入精度更高的模式，如果noHZ可以使能，hrtimer高精度可以使能，即进入NOHZ_MODE_HIGHRES模式：“td=period模式, dev=oneshot模式, hrtimer=high res, noHz=en”。</p>
<p><img src="clockevent_NOHZ_MODE_HIGHRES.png" alt="image"></p>
<p>NOHZ_MODE_HIGHRES：</p>
<ul>
<li>tick_device工作在oneshot模式，HW local timer工作在oneshot模式；</li>
<li>noHZ使能，进入idle不会被tick timer中断打断；</li>
<li>hrtimer工作在高精度模式，和硬件定时器(HWlocal timer)的精度一样，远大于低精度定时器tick精度；</li>
</ul>
<p>为了支持hrtimer的高精度模式，hrtimer必须直接使用tick_device的oneshot模式，而常规的tick timer转换成hrtimer的一个子timer。</p>
<p><img src="ftrace_NOHZ_MODE_HIGHRES.png" alt="image"></p>
<p>上图是NOHZ_MODE_HIGHRES模式下，用ftrace抓取HW timer硬件中断和tick任务的执行情况：</p>
<ul>
<li>tick任务是以固定周期4ms固定执行的；</li>
<li>遇到tick任务超过4ms的间隔，这时就是进入了idle状态，且发生了noHZ(tickless)；</li>
<li>硬件timer中断的发生周期是不固定的，是和hrtimer绑定的；</li>
<li>发生tick的时候肯定发生了timer硬中断，因为tick是其中一个hrtimer；</li>
</ul>
<h4 id="3-3-4、Mode切换"><a href="#3-3-4、Mode切换" class="headerlink" title="3.3.4、Mode切换"></a>3.3.4、Mode切换</h4><p>系统初始状态工作在NOHZ_MODE_INACTIVE模式时，会动态检测是否可以进入更高级别的模式NOHZ_MODE_LOWRES、NOHZ_MODE_HIGHRES。这个检测工作是在这个路径中做的：tick_device工作在period模式：tick_handle_periodic() -> tick_periodic() -> update_process_times() -> run_local_timers() -> hrtimer_run_queues()</p>
<figure class="highlight smali"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br></pre></td><td class="code"><pre><span class="line">void hrtimer_run_queues(void)</span><br><span class="line">{</span><br><span class="line"> struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);</span><br><span class="line"> ktime_t now;</span><br><span class="line"></span><br><span class="line"> /* (3) 如果hrtimer已经切换到高精度模式，</span><br><span class="line"> 则不会从run_local_timers()低精度定时器路径来运行hrtimer */</span><br><span class="line"><span class="built_in"> if </span>(__hrtimer_hres_active(cpu_base))</span><br><span class="line"> return;</span><br><span class="line"></span><br><span class="line"> /*</span><br><span class="line"> * This _is_ ugly: We have to<span class="built_in"> check </span>periodically, whether we</span><br><span class="line"> * can switch to highres<span class="built_in"> and </span>/<span class="built_in"> or </span>nohz mode. The clocksource</span><br><span class="line"> * switch happens with xtime_lock held. Notification from</span><br><span class="line"> * there only sets the<span class="built_in"> check </span>bit in the tick_oneshot code,</span><br><span class="line"> * otherwise we might deadlock vs. xtime_lock.</span><br><span class="line"> */</span><br><span class="line"> </span><br><span class="line"> /* (1) 如果hrtimer没有使能、noHZ使能，</span><br><span class="line"> 则调用：tick_check_oneshot_change() -> tick_nohz_switch_to_nohz()，</span><br><span class="line"> 切换到NOHZ_MODE_LOWRES模式 */</span><br><span class="line"><span class="built_in"> if </span>(tick_check_oneshot_change(!hrtimer_is_hres_enabled())) {</span><br><span class="line"> </span><br><span class="line"> /* (2) 如果hrtimer使能、noHZ使能，</span><br><span class="line"> 则调用：hrtimer_switch_to_hres()，</span><br><span class="line"> 切换到NOHZ_MODE_HIGHRES模式 */</span><br><span class="line"> hrtimer_switch_to_hres();</span><br><span class="line"> return;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> raw_spin_lock(&cpu_base->lock);</span><br><span class="line"> now = hrtimer_update_base(cpu_base);</span><br><span class="line"> /* (4) 低精度hrtimer的运行函数 */</span><br><span class="line"> __hrtimer_run_queues(cpu_base, now);</span><br><span class="line"> raw_spin_unlock(&cpu_base->lock);</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h2 id="4、noHZ"><a href="#4、noHZ" class="headerlink" title="4、noHZ"></a>4、noHZ</h2><p>系统在NOHZ_MODE_LOWRES、NOHZ_MODE_HIGHRES两种模式下支持noHZ。noHZ是一个功耗优化的feature，在系统负载比较轻的时候没有任务需要调度cpu会进入idle状态，但是系统的tick任务(update_process_times())默认会以固定周期执行，这种固定周期会打断idle状态让系统恢复成正常耗电状态。</p>
<p>tick任务这种不管有没有任务都是固定周期运行的特性是需要改进的，noHZ就是为了解决这一问题而产生的：如果在idle状态的过程中tick任务没有到期需要处理的低精度timer和高精度timer，tick任务可以继续保持睡眠，直到真正有timer到期。</p>
<p>idle进程的主要执行序列如下：</p>
<figure class="highlight scss"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line">static void <span class="built_in">cpu_idle_loop</span>(void)</span><br><span class="line">{</span><br><span class="line"> while (<span class="number">1</span>) {</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 进入idle前,noHZ的处理 */</span></span><br><span class="line"> <span class="built_in">tick_nohz_idle_enter</span>();</span><br><span class="line"></span><br><span class="line"> while (!need_resched()) {</span><br><span class="line"> <span class="built_in">check_pgt_cache</span>();</span><br><span class="line"> <span class="built_in">rmb</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2) cpu hotplug之cpu_down()的处理 */</span></span><br><span class="line"> if (cpu_is_offline(smp_processor_id())) {</span><br><span class="line"></span><br><span class="line"> <span class="built_in">arch_cpu_idle_dead</span>();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="built_in">local_irq_disable</span>();</span><br><span class="line"> <span class="built_in">arch_cpu_idle_enter</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (3) cpu idle的进入 */</span></span><br><span class="line"> if (cpu_idle_force_poll || tick_check_broadcast_expired())</span><br><span class="line"> <span class="built_in">cpu_idle_poll</span>();</span><br><span class="line"> else</span><br><span class="line"> <span class="built_in">cpuidle_idle_call</span>();</span><br><span class="line"></span><br><span class="line"> <span class="built_in">arch_cpu_idle_exit</span>();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (4) 退出idle后,noHZ的处理 */</span></span><br><span class="line"> <span class="built_in">tick_nohz_idle_exit</span>();</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>可以看到，其中的关键在tick_nohz_idle_enter()/tick_nohz_idle_exit()函数。</p>
<h3 id="4-1、tick-nohz-idle-enter-exit"><a href="#4-1、tick-nohz-idle-enter-exit" class="headerlink" title="4.1、tick_nohz_idle_enter/exit()"></a>4.1、tick_nohz_idle_enter/exit()</h3><p>tick_nohz_idle_enter()的解析：</p>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br></pre></td><td class="code"><pre><span class="line">void tick_nohz_idle_enter(void)</span><br><span class="line">{</span><br><span class="line"> struct tick_sched *ts;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> ts = this_cpu_ptr(&tick_cpu_sched);</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>inidle = <span class="number">1</span>;</span><br><span class="line"> __tick_nohz_idle_enter(ts);</span><br><span class="line"></span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">static void __tick_nohz_idle_enter(struct tick_sched *ts)</span><br><span class="line">{</span><br><span class="line"> ktime_t now, expires;</span><br><span class="line"> int cpu = smp_processor_id();</span><br><span class="line"></span><br><span class="line"> now = tick_nohz_start_idle(ts);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 判断当前能否stop tick任务 */</span></span><br><span class="line"> <span class="keyword">if</span> (can_stop_idle_tick(cpu, ts)) {</span><br><span class="line"> <span class="function"><span class="title">int</span> was_stopped = ts-></span>tick_stopped;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>idle_calls++;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2) 尝试stop tick任务 */</span></span><br><span class="line"> expires = tick_nohz_stop_sched_tick(ts, now, cpu);</span><br><span class="line"> <span class="keyword">if</span> (expires.tv64 > <span class="number">0</span>LL) {</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>idle_sleeps++;</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>idle_expires = expires;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (!was_stopped && ts-></span>tick_stopped)</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span><span class="function"><span class="title">idle_jiffies</span> = ts-></span>last_jiffies;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line">static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,</span><br><span class="line"> ktime_t now, int cpu)</span><br><span class="line">{</span><br><span class="line"> struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);</span><br><span class="line"> u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;</span><br><span class="line"> unsigned long seq, basejiff;</span><br><span class="line"> ktime_t tick;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Read jiffies and the time when jiffies were updated last */</span></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> seq = read_seqbegin(&jiffies_lock);</span><br><span class="line"> basemono = last_jiffies_update.tv64;</span><br><span class="line"> basejiff = jiffies;</span><br><span class="line"> } <span class="keyword">while</span> (read_seqretry(&jiffies_lock, seq));</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>last_jiffies = basejiff;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (rcu_needs_cpu(basemono, &next_rcu) ||</span><br><span class="line"> arch_needs_cpu() || irq_work_needs_cpu()) {</span><br><span class="line"> next_tick = basemono + TICK_NSEC;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Get the next pending timer. If high resolution</span></span><br><span class="line"><span class="comment"> * timers are enabled this only takes the timer wheel</span></span><br><span class="line"><span class="comment"> * timers into account. If high resolution timers are</span></span><br><span class="line"><span class="comment"> * disabled this also looks at the next expiring</span></span><br><span class="line"><span class="comment"> * hrtimer.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.1) 获取下一个timer的到期时间(包括低精度和高精度timer) */</span></span><br><span class="line"> next_tmr = get_next_timer_interrupt(basejiff, basemono);</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>next_timer = next_tmr;</span><br><span class="line"> <span class="comment">/* Take the next rcu event into account */</span></span><br><span class="line"> next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * If the tick is due in the next period, keep it ticking or</span></span><br><span class="line"><span class="comment"> * restart it proper.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.2) 如果差距小于一个tick，不需要进入noHZ模式 */</span></span><br><span class="line"> delta = next_tick - basemono;</span><br><span class="line"> <span class="keyword">if</span> (delta <= (u64)TICK_NSEC) {</span><br><span class="line"> tick.tv64 = <span class="number">0</span>;</span><br><span class="line"> <span class="function"><span class="title">if</span> (!ts-></span>tick_stopped)</span><br><span class="line"> goto out;</span><br><span class="line"> <span class="keyword">if</span> (delta == <span class="number">0</span>) {</span><br><span class="line"> <span class="comment">/* Tick is stopped, but required now. Enforce it */</span></span><br><span class="line"> tick_nohz_restart(ts, now);</span><br><span class="line"> goto out;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * If this cpu is the one which updates jiffies, then give up</span></span><br><span class="line"><span class="comment"> * the assignment and let it be taken by the cpu which runs</span></span><br><span class="line"><span class="comment"> * the tick timer next, which might be this cpu as well. If we</span></span><br><span class="line"><span class="comment"> * don't drop this here the jiffies might be stale and</span></span><br><span class="line"><span class="comment"> * do_timer() never invoked. Keep track of the fact that it</span></span><br><span class="line"><span class="comment"> * was the one which had the do_timer() duty last. If this cpu</span></span><br><span class="line"><span class="comment"> * is the one which had the do_timer() duty last, we limit the</span></span><br><span class="line"><span class="comment"> * sleep time to the timekeeping max_deferement value.</span></span><br><span class="line"><span class="comment"> * Otherwise we can sleep as long as we want.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">/* (2.3) 根据timekeeper的可能溢出的位宽，得到的idle最大值 */</span></span><br><span class="line"> delta = timekeeping_max_deferment();</span><br><span class="line"> <span class="keyword">if</span> (cpu == tick_do_timer_cpu) {</span><br><span class="line"> tick_do_timer_cpu = TICK_DO_TIMER_NONE;</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>do_timer_last = <span class="number">1</span>;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {</span><br><span class="line"> delta = KTIME_MAX;</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>do_timer_last = <span class="number">0</span>;</span><br><span class="line"> } <span class="function"><span class="title">else</span> <span class="keyword">if</span> (!ts-></span>do_timer_last) {</span><br><span class="line"> delta = KTIME_MAX;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line">#ifdef CONFIG_NO_HZ_FULL</span><br><span class="line"> <span class="comment">/* Limit the tick delta to the maximum scheduler deferment */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (!ts-></span>inidle)</span><br><span class="line"> delta = min(delta, scheduler_tick_max_deferment());</span><br><span class="line">#endif</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Calculate the next expiry time */</span></span><br><span class="line"> <span class="keyword">if</span> (delta < (KTIME_MAX - basemono))</span><br><span class="line"> expires = basemono + delta;</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> expires = KTIME_MAX;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.4) 综合上面条件，得到合理的stop tick的时间 */</span></span><br><span class="line"> expires = min_t(u64, expires, next_tick);</span><br><span class="line"> tick.tv64 = expires;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Skip reprogram of event if its not changed */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span><span class="function"><span class="title">tick_stopped</span> && (expires == dev-></span>next_event.tv64))</span><br><span class="line"> goto out;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * nohz_stop_sched_tick can be called several times before</span></span><br><span class="line"><span class="comment"> * the nohz_restart_sched_tick is called. This happens when</span></span><br><span class="line"><span class="comment"> * interrupts arrive which do not cause a reschedule. In the</span></span><br><span class="line"><span class="comment"> * first call we save the current tick time, so we can restart</span></span><br><span class="line"><span class="comment"> * the scheduler tick in nohz_restart_sched_tick.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (!ts-></span>tick_stopped) {</span><br><span class="line"> nohz_balance_enter_idle(cpu);</span><br><span class="line"> calc_load_enter_idle();</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span><span class="function"><span class="title">last_tick</span> = hrtimer_get_expires(&ts-></span>sched_timer);</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>tick_stopped = <span class="number">1</span>;</span><br><span class="line"> trace_tick_stop(<span class="number">1</span>, <span class="string">" "</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * If the expiration time == KTIME_MAX, then we simply stop</span></span><br><span class="line"><span class="comment"> * the tick timer.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (unlikely(expires == KTIME_MAX)) {</span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span>nohz_mode == NOHZ_MODE_HIGHRES)</span><br><span class="line"> <span class="function"><span class="title">hrtimer_cancel</span>(&ts-></span>sched_timer);</span><br><span class="line"> goto out;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2.5) 实际的stop tick动作：</span></span><br><span class="line"><span class="comment"> 将local timer的周期改为大于一个tick的时间，将idle时间延长 */</span></span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span>nohz_mode == NOHZ_MODE_HIGHRES)</span><br><span class="line"> <span class="function"><span class="title">hrtimer_start</span>(&ts-></span>sched_timer, tick, HRTIMER_MODE_ABS_PINNED);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> tick_program_event(tick, <span class="number">1</span>);</span><br><span class="line">out:</span><br><span class="line"> <span class="comment">/* Update the estimated sleep length */</span></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span><span class="function"><span class="title">sleep_length</span> = ktime_sub(dev-></span>next_event, now);</span><br><span class="line"> return tick;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>tick_nohz_idle_exit()的解析：</p>
<figure class="highlight xl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br></pre></td><td class="code"><pre><span class="line">void tick_nohz_idle_exit(void)</span><br><span class="line">{</span><br><span class="line"> struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);</span><br><span class="line"> ktime_t now;</span><br><span class="line"></span><br><span class="line"> local_irq_disable();</span><br><span class="line"></span><br><span class="line"> WARN_ON_ONCE(!<span class="function"><span class="title">ts</span>-></span>inidle);</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>inidle = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span><span class="function"><span class="title">idle_active</span> || ts-></span>tick_stopped)</span><br><span class="line"> now = ktime_get();</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span>idle_active)</span><br><span class="line"> tick_nohz_stop_idle(ts, now);</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span>tick_stopped) {</span><br><span class="line"> <span class="comment">/* (1) 重启tick任务 */</span></span><br><span class="line"> tick_nohz_restart_sched_tick(ts, now);</span><br><span class="line"> tick_nohz_account_idle_ticks(ts);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> local_irq_enable();</span><br><span class="line">}</span><br><span class="line">|→</span><br><span class="line">static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)</span><br><span class="line">{</span><br><span class="line"> <span class="comment">/* Update jiffies first */</span></span><br><span class="line"> tick_do_update_jiffies64(now);</span><br><span class="line"> update_cpu_load_nohz();</span><br><span class="line"></span><br><span class="line"> calc_load_exit_idle();</span><br><span class="line"> touch_softlockup_watchdog();</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Cancel the scheduled timer and restore the tick</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>tick_stopped = <span class="number">0</span>;</span><br><span class="line"> <span class="function"><span class="title">ts</span>-></span>idle_exittime = now;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1.1) 重启local timer */</span></span><br><span class="line"> tick_nohz_restart(ts, now);</span><br><span class="line">}</span><br><span class="line">||→</span><br><span class="line">static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)</span><br><span class="line">{</span><br><span class="line"> <span class="function"><span class="title">hrtimer_cancel</span>(&ts-></span>sched_timer);</span><br><span class="line"> <span class="function"><span class="title">hrtimer_set_expires</span>(&ts-></span><span class="function"><span class="title">sched_timer</span>, ts-></span>last_tick);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Forward the time to expire in the future */</span></span><br><span class="line"> <span class="function"><span class="title">hrtimer_forward</span>(&ts-></span>sched_timer, now, tick_period);</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="title">if</span> (ts-></span>nohz_mode == NOHZ_MODE_HIGHRES)</span><br><span class="line"> <span class="function"><span class="title">hrtimer_start_expires</span>(&ts-></span>sched_timer, HRTIMER_MODE_ABS_PINNED);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="function"><span class="title">tick_program_event</span>(hrtimer_get_expires(&ts-></span>sched_timer), <span class="number">1</span>);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="4-2-tick-nohz-irq-enter-exit"><a href="#4-2-tick-nohz-irq-enter-exit" class="headerlink" title="4.2 tick_nohz_irq_enter/exit()"></a>4.2 tick_nohz_irq_enter/exit()</h3><p>因为在idle退出执行完本tick需要处理的timer后又需要重新关闭tick，系统设计了tick_nohz_irq_enter()/tick_nohz_irq_exit()来处理这种操作。在本次中断处理完timer后，在tick_nohz_irq_exit()中判断是否重新关闭tick任务。</p>
<figure class="highlight scss"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line">static void <span class="built_in">cpu_idle_loop</span>(void)</span><br><span class="line">{</span><br><span class="line"> while (<span class="number">1</span>) {</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 关闭tick */</span></span><br><span class="line"> <span class="built_in">tick_nohz_idle_enter</span>();</span><br><span class="line"></span><br><span class="line"> while (!need_resched()) {</span><br><span class="line"> <span class="built_in">check_pgt_cache</span>();</span><br><span class="line"> <span class="built_in">rmb</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2) cpu hotplug之cpu_down()的处理 */</span></span><br><span class="line"> if (cpu_is_offline(smp_processor_id())) {</span><br><span class="line"></span><br><span class="line"> <span class="built_in">arch_cpu_idle_dead</span>();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (3) 关中断 */</span></span><br><span class="line"> <span class="built_in">local_irq_disable</span>();</span><br><span class="line"> <span class="built_in">arch_cpu_idle_enter</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (4) 进入idle，</span></span><br><span class="line"><span class="comment"> cpu进入暂停状态 */</span></span><br><span class="line"> if (cpu_idle_force_poll || tick_check_broadcast_expired())</span><br><span class="line"> <span class="built_in">cpu_idle_poll</span>();</span><br><span class="line"> else</span><br><span class="line"> <span class="built_in">cpuidle_idle_call</span>();</span><br><span class="line"> <span class="comment">/* (5) cpu被local timer中断唤醒退出idle状态，继续执行；</span></span><br><span class="line"><span class="comment"> 但是因为irq是disable状态，中断服务程序并不能马上得到执行*/</span></span><br><span class="line"> <span class="comment">/* (5.1) 退出idle，并且开中断 */</span> </span><br><span class="line"> </span><br><span class="line"> <span class="comment">/* (6) 中断打开后，被阻塞的local timer中断服务得到执行，到期的软件timer得到执行；*/</span></span><br><span class="line"> <span class="comment">/* (6.1) 退出中断时调用tick_nohz_irq_exit()，重新计算一个tick可以被stop的值 */</span></span><br><span class="line"> </span><br><span class="line"> <span class="built_in">arch_cpu_idle_exit</span>();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (7) 重启tick */</span></span><br><span class="line"> <span class="built_in">tick_nohz_idle_exit</span>();</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>tick_nohz_irq_enter()/tick_nohz_irq_exit()的代码解析：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">static</span> <span class="keyword">inline</span> <span class="type">void</span> <span class="title">tick_nohz_irq_enter</span><span class="params">(<span class="type">void</span>)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">tick_sched</span> *ts = <span class="built_in">this_cpu_ptr</span>(&tick_cpu_sched);</span><br><span class="line"> <span class="type">ktime_t</span> now;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!ts->idle_active && !ts->tick_stopped)</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> now = <span class="built_in">ktime_get</span>();</span><br><span class="line"> <span class="keyword">if</span> (ts->idle_active)</span><br><span class="line"> <span class="built_in">tick_nohz_stop_idle</span>(ts, now);</span><br><span class="line"> </span><br><span class="line"> <span class="comment">/* (1) 基本就是空操作 */</span></span><br><span class="line"> <span class="keyword">if</span> (ts->tick_stopped) {</span><br><span class="line"> <span class="built_in">tick_nohz_update_jiffies</span>(now);</span><br><span class="line"> <span class="built_in">tick_nohz_kick_tick</span>(ts, now);</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">tick_nohz_irq_exit</span><span class="params">(<span class="type">void</span>)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">tick_sched</span> *ts = <span class="built_in">this_cpu_ptr</span>(&tick_cpu_sched);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (ts->inidle)</span><br><span class="line"> <span class="comment">/* (2) 重新判断stop tick任务 */</span></span><br><span class="line"> __tick_nohz_idle_enter(ts);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="built_in">tick_nohz_full_update_tick</span>(ts);</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h3 id="4-3、local-timer时钟被关闭时的处理"><a href="#4-3、local-timer时钟被关闭时的处理" class="headerlink" title="4.3、local timer时钟被关闭时的处理"></a>4.3、local timer时钟被关闭时的处理</h3><p>还有一种情况需要考虑，在系统进入深层次的idle状态时，local timer本身的时钟可能会被关闭。比如MTK平台进入soidle状态时，local timer本身会被停止，这时会用一个GPT timer来替代local timer继续工作。</p>
<p>核心函数是timer_setting_before_wfi()/timer_setting_after_wfi()：</p>
<ul>
<li>timer_setting_before_wfi()在进入idle前被调用，读出local timer的剩余值并配置到GPT timer中；</li>
<li>timer_setting_after_wfi()在退出idle后被调用，读出GPT timer的值来重新恢复local timer；</li>
</ul>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="function"><span class="type">static</span> <span class="type">void</span> <span class="title">timer_setting_before_wfi</span><span class="params">(<span class="type">bool</span> f26m_off)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"><span class="meta">#<span class="keyword">ifndef</span> USING_STD_TIMER_OPS</span></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_SMP</span></span><br><span class="line"> <span class="type">unsigned</span> <span class="type">int</span> timer_left = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (1) 读出local timer的剩余值 */</span></span><br><span class="line"> timer_left = <span class="built_in">localtimer_get_counter</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (2) 根据GPT timer在不同状态下的频率，把剩余值配置到GPT中 */</span></span><br><span class="line"> <span class="keyword">if</span> ((<span class="type">int</span>)timer_left <= <span class="number">0</span>)</span><br><span class="line"> <span class="built_in">gpt_set_cmp</span>(IDLE_GPT, <span class="number">1</span>); <span class="comment">/* Trigger idle_gpt Timeout imediately */</span></span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">if</span> (f26m_off)</span><br><span class="line"> <span class="built_in">gpt_set_cmp</span>(IDLE_GPT, <span class="built_in">div_u64</span>(timer_left, <span class="number">406.25</span>));</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="built_in">gpt_set_cmp</span>(IDLE_GPT, timer_left);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (f26m_off)</span><br><span class="line"> <span class="built_in">gpt_set_clk</span>(IDLE_GPT, GPT_CLK_SRC_RTC, GPT_CLK_DIV_1);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">start_gpt</span>(IDLE_GPT);</span><br><span class="line"><span class="meta">#<span class="keyword">else</span></span></span><br><span class="line"> <span class="built_in">gpt_get_cnt</span>(GPT1, &timer_left);</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">static</span> <span class="type">void</span> <span class="title">timer_setting_after_wfi</span><span class="params">(<span class="type">bool</span> f26m_off)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"><span class="meta">#<span class="keyword">ifndef</span> USING_STD_TIMER_OPS</span></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_SMP</span></span><br><span class="line"> <span class="comment">/* (3) 判断当前退出idle状态是否是因为GPT到期引起的 */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">gpt_check_and_ack_irq</span>(IDLE_GPT)) {</span><br><span class="line"> <span class="comment">/* (3.1) 如果GPT时间已经到期，证明local timer也已经到期，</span></span><br><span class="line"><span class="comment"> 触发local timer在下一时钟执行 */</span></span><br><span class="line"> <span class="built_in">localtimer_set_next_event</span>(<span class="number">1</span>);</span><br><span class="line"> <span class="keyword">if</span> (f26m_off)</span><br><span class="line"> <span class="built_in">gpt_set_clk</span>(IDLE_GPT, GPT_CLK_SRC_SYS, GPT_CLK_DIV_1);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">/* (4) 退出idle是因为GPT以外的中断源唤醒的 */</span></span><br><span class="line"> <span class="comment">/* waked up by other wakeup source */</span></span><br><span class="line"> <span class="type">unsigned</span> <span class="type">int</span> cnt, cmp;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* (4.1) 读出GPT中的剩余到期值，重新配置到local timer中 */</span></span><br><span class="line"> <span class="built_in">idle_gpt_get_cnt</span>(IDLE_GPT, &cnt);</span><br><span class="line"> <span class="built_in">idle_gpt_get_cmp</span>(IDLE_GPT, &cmp);</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">unlikely</span>(cmp < cnt)) {</span><br><span class="line"> <span class="built_in">idle_err</span>(<span class="string">"[%s]GPT%d: counter = %10u, compare = %10u\n"</span>,</span><br><span class="line"> __func__, IDLE_GPT + <span class="number">1</span>, cnt, cmp);</span><br><span class="line"> <span class="comment">/* BUG(); */</span></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (f26m_off) {</span><br><span class="line"> <span class="built_in">localtimer_set_next_event</span>((cmp - cnt) * <span class="number">1625</span> / <span class="number">4</span>);</span><br><span class="line"> <span class="built_in">gpt_set_clk</span>(IDLE_GPT, GPT_CLK_SRC_SYS, GPT_CLK_DIV_1);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="built_in">localtimer_set_next_event</span>(cmp - cnt);</span><br><span class="line"> }</span><br><span class="line"> <span class="built_in">stop_gpt</span>(IDLE_GPT);</span><br><span class="line"> }</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<p>需要特别说明的是，这种GPT timer全局只有一个，进入soidle的状态时cpu也只有一个在线，所以能正常的工作。</p>
<h2 id="5、hrtimer"><a href="#5、hrtimer" class="headerlink" title="5、hrtimer"></a>5、hrtimer</h2><h3 id="5-1、hrtimer的组织"><a href="#5-1、hrtimer的组织" class="headerlink" title="5.1、hrtimer的组织"></a>5.1、hrtimer的组织</h3><p>hrtimer的组织相对来说还是比较简单的，每个cpu对应一个hrtimer_cpu_base，每个hrtimer_cpu_base中有4类clock_base代表4种时间类型(HRTIMER_BASE_REALTIME、HRTIMER_BASE_MONOTONIC、HRTIMER_BASE_BOOTTIME、HRTIMER_BASE_TAI)的hrtimer，每个clock_base是以红黑树来组织同一类型的hrtimer的：</p>
<p><img src="hrtimer.png" alt="image"></p>
<figure class="highlight x86asm"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line">DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =</span><br><span class="line">{</span><br><span class="line"><span class="meta"> .lock</span> = __RAW_SPIN_LOCK_UNLOCKED(hrtimer_bases<span class="number">.</span><span class="keyword">lock</span>),</span><br><span class="line"><span class="meta"> .seq</span> = SEQCNT_ZERO(hrtimer_bases<span class="number">.</span>seq),</span><br><span class="line"><span class="meta"> .clock_base</span> =</span><br><span class="line"> {</span><br><span class="line"> {</span><br><span class="line"><span class="meta"> .index</span> = HRTIMER_BASE_MONOTONIC,</span><br><span class="line"><span class="meta"> .clockid</span> = CLOCK_MONOTONIC,</span><br><span class="line"><span class="meta"> .get_time</span> = &ktime_get,</span><br><span class="line"> },</span><br><span class="line"> {</span><br><span class="line"><span class="meta"> .index</span> = HRTIMER_BASE_REALTIME,</span><br><span class="line"><span class="meta"> .clockid</span> = CLOCK_REALTIME,</span><br><span class="line"><span class="meta"> .get_time</span> = &ktime_get_real,</span><br><span class="line"> },</span><br><span class="line"> {</span><br><span class="line"><span class="meta"> .index</span> = HRTIMER_BASE_BOOTTIME,</span><br><span class="line"><span class="meta"> .clockid</span> = CLOCK_BOOTTIME,</span><br><span class="line"><span class="meta"> .get_time</span> = &ktime_get_boottime,</span><br><span class="line"> },</span><br><span class="line"> {</span><br><span class="line"><span class="meta"> .index</span> = HRTIMER_BASE_TAI,</span><br><span class="line"><span class="meta"> .clockid</span> = CLOCK_TAI,</span><br><span class="line"><span class="meta"> .get_time</span> = &ktime_get_clocktai,</span><br><span class="line"> },</span><br><span class="line"> }</span><br><span class="line">}<span class="comment">;</span></span><br></pre></td></tr></table></figure>
<h3 id="5-2、低精度模式-NOHZ-MODE-INACTIVE-NOHZ-MODE-LOWRES"><a href="#5-2、低精度模式-NOHZ-MODE-INACTIVE-NOHZ-MODE-LOWRES" class="headerlink" title="5.2、低精度模式(NOHZ_MODE_INACTIVE/NOHZ_MODE_LOWRES)"></a>5.2、低精度模式(NOHZ_MODE_INACTIVE/NOHZ_MODE_LOWRES)</h3><p>前面几章已经详细描述了执行路径，在低精度模式下hrtimer的实际精度和低精度定时器是一样的，都是基于tick精度的。他的执行路径如下。</p>
<p>NOHZ_MODE_INACTIVE模式：</p>
<figure class="highlight stylus"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">tick_handle_periodic</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">tick_periodic</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">update_process_times</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">run_local_timers</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">hrtimer_run_queues</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="built_in">__hrtimer_run_queues</span>()</span><br></pre></td></tr></table></figure>
<p>NOHZ_MODE_LOWRES模式：</p>
<figure class="highlight stylus"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">tick_nohz_handler</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">tick_sched_handle</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">update_process_times</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">run_local_timers</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">hrtimer_run_queues</span><span class="params">()</span></span></span><br><span class="line"> ↓</span><br><span class="line"><span class="built_in">__hrtimer_run_queues</span>()</span><br></pre></td></tr></table></figure>
<h3 id="5-3、高精度模式-NOHZ-MODE-HIGHRES"><a href="#5-3、高精度模式-NOHZ-MODE-HIGHRES" class="headerlink" title="5.3、高精度模式(NOHZ_MODE_HIGHRES)"></a>5.3、高精度模式(NOHZ_MODE_HIGHRES)</h3><p>在高精度模式下hrtimer才能发挥出真正的精度，他的可以精确定时到小于一个tick，精度依赖于硬件local timer。</p>
<p>NOHZ_MODE_LOWRES模式：</p>
<figure class="highlight isbl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">hrtimer_interrupt</span>()</span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">__hrtimer_run_queues</span>()</span></span><br></pre></td></tr></table></figure>
<h2 id="6、低精度timer-lowres-timer"><a href="#6、低精度timer-lowres-timer" class="headerlink" title="6、低精度timer(lowres timer)"></a>6、低精度timer(lowres timer)</h2><p>低精度timer在系统中的应用范围更广，若非特别声明是hrtimer其他都是使用低精度timer，类如schedule_timeout()、msleep()。他有以下特点：</p>
<ul>
<li>精度低，以tick为单位计时；</li>
<li>执行上下文，低精度timer执行时是在softirq中，而hrtimer的实际执行是在中断当中。所以低精度的执行精度更小于hrtimer；</li>
<li>对系统的实时影响小，softirq比irq对系统的实时性影响更小；</li>
</ul>
<h3 id="6-1、低精度timer的组织"><a href="#6-1、低精度timer的组织" class="headerlink" title="6.1、低精度timer的组织"></a>6.1、低精度timer的组织</h3><p>低精度timer的组织形式和hrtimer类似，只是timer的链接不是采用红黑树，而是采用tv1 - tv5等一系列的链表。</p>
<p><img src="lowres_timer.png" alt="image"></p>
<p>tv1 - tv5中保留着一系列槽位，每个槽位代表一个超时时间，把相同超时时间的低精度timer链接到同一槽位当中。</p>
<h3 id="6-2、低精度timer的执行路径"><a href="#6-2、低精度timer的执行路径" class="headerlink" title="6.2、低精度timer的执行路径"></a>6.2、低精度timer的执行路径</h3><p>低精度timer的实际执行时在softirq中执行的，在中断中的动作只是简单触发softirq。</p>
<p>中断中：</p>
<figure class="highlight isbl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="title">tick_handle_periodic</span>()/<span class="title">tick_nohz_handler</span>()/<span class="title">hrtimer_interrupt</span>()</span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">run_local_timers</span>()</span></span><br><span class="line"> ↓</span><br><span class="line"><span class="function"><span class="title">raise_softirq</span>(<span class="variable">TIMER_SOFTIRQ</span>);</span></span><br></pre></td></tr></table></figure>
<p>软中断中：</p>
<figure class="highlight perl"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">run_timer_softir<span class="string">q()</span></span><br><span class="line"> ↓</span><br><span class="line">__run_timers()</span><br></pre></td></tr></table></figure>
<h2 id="参考资料"><a href="#参考资料" class="headerlink" title="参考资料"></a>参考资料</h2><p>[^DroidPhoneo]: <a href="http://blog.csdn.net/DroidPhone/article/category/1263459">Linux 时间子系统</a></p>
<p>[^wowo]: <a href="http://www.wowotech.net/timer_subsystem/time_subsystem_index.html">wowotech time subsystem</a></p>
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font-size: 1.1em;
margin-top : -0.1em;
}
}
</style>
<!-- Footer -->
<!-- Footer -->
<footer>
<div class="container">
<div class="row">
<div class="col-lg-8 col-lg-offset-2 col-md-10 col-md-offset-1">
<ul class="list-inline text-center">
</ul>
<p class="copyright text-muted">
Copyright © meizu 2024
<br>
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<a href="https://github.com/dusign/hexo-theme-snail">
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<iframe name="star" style="margin-left: 2px; margin-bottom:-5px;" frameborder="0" scrolling="0"
width="100px" height="20px"
src="https://ghbtns.com/github-btn.html?user=dusign&repo=hexo-theme-snail&type=star&count=true">
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</p>
</div>
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</footer>
<!-- jQuery -->
<script src="js/jquery.min.js"></script>
<!-- Bootstrap Core JavaScript -->
<script src="js/bootstrap.min.js"></script>
<!-- Custom Theme JavaScript -->
<script src="js/hux-blog.min.js"></script>
<!-- Search -->
<script src="js/search.js"></script>
<!-- async load function -->
<script>
function async(u, c) {
var d = document, t = 'script',
o = d.createElement(t),
s = d.getElementsByTagName(t)[0];
o.src = u;
if (c) { o.addEventListener('load', function (e) { c(null, e); }, false); }
s.parentNode.insertBefore(o, s);
}
</script>
<!-- jquery.tagcloud.js -->
<script>
// only load tagcloud.js in tag.html
if($('#tag_cloud').length !== 0){
async("https://kernel.meizu.com/js/jquery.tagcloud.js",function(){
$.fn.tagcloud.defaults = {
//size: {start: 1, end: 1, unit: 'em'},
color: {start: '#bbbbee', end: '#0085a1'},
};
$('#tag_cloud a').tagcloud();
})
}
</script>
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<script>
async("https://cdn.bootcss.com/fastclick/1.0.6/fastclick.min.js", function(){
var $nav = document.querySelector("nav");
if($nav) FastClick.attach($nav);
})
</script>
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<script>
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var _gaDomain = 'yoursite';
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})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
ga('create', _gaId, _gaDomain);
ga('send', 'pageview');
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<script type="text/javascript">
var search_path = "search.xml";
if (search_path.length == 0) {
search_path = "search.xml";
}
var path = "/" + search_path;
searchFunc(path, 'local-search-input', 'local-search-result');
</script>
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<script async src="//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script>
<a id="rocket" href="#top" class=""></a>
<script type="text/javascript" src="/js/totop.js?v=1.0.0" async=""></script>
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<script src="/js/ribbonDynamic.js"></script>
</body>
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