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Linux Interrupt - 魅族内核团队
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<h1>Linux Interrupt</h1>
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Posted by Peng Weilin on
2016-09-02
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<p>在面试的时候我们常常被问及一个问题：几种中断下半部机制 softirq、tasklet、workqueue 有什么区别？Linux 为什么要设计这几种机制？真正能够回答清楚的人还是少数的。下面我们就详细分析一下这其中的区别。</p>
<blockquote>
<p>本文的代码分析基于 Linux kernel 3.18.22 和 arm64 架构，最好的学习方法还是 “RTFSC”</p>
</blockquote>
<h2 id="1-Linux-中断"><a href="#1-Linux-中断" class="headerlink" title="1. Linux 中断"></a>1. Linux 中断</h2><p>arm64 和其他所有 CPU 架构的中断处理流程都是一样：正常执行流程被打断进入中断服务程序，保护现场、处理中断、恢复现场：</p>
<p><img src="int_handler.png" alt=" 中断处理">[^ARMPG]</p>
<p>在整个中断处理过程中，arm64 的 CPU 全局中断是自动 disable 的 (PSTATE 寄存器中的 interrupt bit 被 masks)。如果用户想支持 interrupt nested，需要自己在中断服务程序中使能中断。Linux 现在是不使用中断嵌套的。</p>
<p><img src="int_nested_handler.png" alt=" 中断嵌套处理 ">[^ARMPG]</p>
<h3 id="1-1-CPU-中断打开-关闭"><a href="#1-1-CPU-中断打开-关闭" class="headerlink" title="1.1 CPU 中断打开 / 关闭"></a>1.1 CPU 中断打开 / 关闭</h3><p>arm64 关闭和打开本地 CPU 的全局中断的方法，是操作 SPSR(Saved Process Status Register) 寄存器 IRQ mask bit。</p>
<p><img src="int_arm64_spsr.png" alt="Arm64 SPSR">[^ARMPG]</p>
<p>Linux 中 arm64 关闭和打开本地 CPU 中断的函数实现。</p>
<ul>
<li>arch/arm64/include/asm/irqflags.h:</li>
<li><code>local_irq_disable()</code> -> <code>raw_local_irq_disable()</code> -> <code>arch_local_irq_disable()</code></li>
<li><code>local_irq_enable()</code> -> <code>raw_local_irq_enable()</code> -> <code>arch_local_irq_enable()</code></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></pre></td><td class="code"><pre><span class="line"></span><br><span class="line"><span class="function"><span class="type">static</span> <span class="keyword">inline</span> <span class="type">void</span> <span class="title">arch_local_irq_enable</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="function"><span class="keyword">asm</span> <span class="title">volatile</span><span class="params">(</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="comment">// (1) 清除 DAIF 中的 bit2 I 标志位，打开中断</span></span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="string">"msr daifclr, #2 // arch_local_irq_enable"</span></span></span></span><br><span class="line"><span class="params"><span class="function"> :</span></span></span><br><span class="line"><span class="params"><span class="function"> :</span></span></span><br><span class="line"><span class="params"><span class="function"> : <span class="string">"memory"</span>)</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="keyword">inline</span> <span class="type">void</span> <span class="title">arch_local_irq_disable</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="function"><span class="keyword">asm</span> <span class="title">volatile</span><span class="params">(</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="comment">// (2) 设置 DAIF 中的 bit2 I 标志位，关闭中断</span></span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="string">"msr daifset, #2 // arch_local_irq_disable"</span></span></span></span><br><span class="line"><span class="params"><span class="function"> :</span></span></span><br><span class="line"><span class="params"><span class="function"> :</span></span></span><br><span class="line"><span class="params"><span class="function"> : <span class="string">"memory"</span>)</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="keyword">inline</span> <span class="type">unsigned</span> <span class="type">long</span> <span class="title">arch_local_irq_save</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="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"> <span class="function"><span class="keyword">asm</span> <span class="title">volatile</span><span class="params">(</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="comment">// (3) 备份 DAIF 标志</span></span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="string">"mrs %0, daif // arch_local_irq_save\n"</span></span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="string">"msr daifset, #2"</span></span></span></span><br><span class="line"><span class="params"><span class="function"> : <span class="string">"=r"</span> (flags)</span></span></span><br><span class="line"><span class="params"><span class="function"> :</span></span></span><br><span class="line"><span class="params"><span class="function"> : <span class="string">"memory"</span>)</span></span>;</span><br><span class="line"> <span class="keyword">return</span> flags;</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="keyword">inline</span> <span class="type">unsigned</span> <span class="type">long</span> <span class="title">arch_local_save_flags</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="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"> <span class="function"><span class="keyword">asm</span> <span class="title">volatile</span><span class="params">(</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="comment">// (4) 恢复 DAIF 标志</span></span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="string">"mrs %0, daif // arch_local_save_flags"</span></span></span></span><br><span class="line"><span class="params"><span class="function"> : <span class="string">"=r"</span> (flags)</span></span></span><br><span class="line"><span class="params"><span class="function"> :</span></span></span><br><span class="line"><span class="params"><span class="function"> : <span class="string">"memory"</span>)</span></span>;</span><br><span class="line"> <span class="keyword">return</span> flags;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="1-2-中断控制器-GIC"><a href="#1-2-中断控制器-GIC" class="headerlink" title="1.2 中断控制器 GIC"></a>1.2 中断控制器 GIC</h3><p>上面描述了 CPU 对全局中断的处理，但是还有一个工作需要有人去做：就是把外部中断、内部中断、CPU 间中断等各种中断按照优先级、亲和力、私有性等发送给多个 CPU。负责这个工作的就是中断控制器 GIC(Generic Interrupt Controller)。</p>
<p><img src="int_gic400.gif" alt="GIC400">[^GICANALY]</p>
<p>从软件角度上看，GIC 可以分成两个功能模块：[^ARMPG]</p>
<ul>
<li>Distributor。负责连接系统中所有的中断源，通过寄存器可以独立的配置每个中断的属性：priority、state、security、outing information、enable status。定义哪些中断可以转发到 CPU core。</li>
<li>CPU Interface。CPU core 用来接收中断，寄存器主要提供的功能：mask、 identify 、control states of interrupts forwarded to that core。每个 CPU core 拥有自己的 CPU interface。</li>
</ul>
<p>对 GIC 来说，中断可以分成以下几种类型：[^ARMPG]</p>
<ul>
<li>SGI(Software Generated Interrupt)，Interrupt IDs 0-15。系统一般用其来实现 IPI 中断。</li>
<li>PPI(Private Peripheral Interrupt)，Interrupt IDs16-31。私有中断，这种中断对每个 CPU 都是独立一份的，比如 per-core timer 中断。</li>
<li>SPI(Shared Peripheral Interrupt)，Interrupt numbers 32-1020。最常用的外设中断，中断可以发给一个或者多个 CPU。</li>
<li>LPI(Locality-specific Peripheral Interrupt)。基于 message 的中断，GICv2 和 GICv1 中不支持。</li>
</ul>
<p>GIC 从原理上理解并不难，但是如果涉及到级联等技术细节，整个初始化过程还是比较复杂。大家可以自行下载 GIC 手册：<a href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0471b/index.html">GIC-400</a>、<a href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0516e/index.html">GIC-500</a> 学习，<a href="http://www.wowotech.net/irq_subsystem/gic_driver.html">GIC 代码分析 </a> 也是一篇很不错的分析文章。</p>
<p>一款 GIC 相关的操作函数都会集中到 irq_chip 数据结构中，以 GIC-400 为例，它的相关操作函数如下：</p>
<ul>
<li>drivers/irqchip/irq-gic.c:</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></pre></td><td class="code"><pre><span class="line"><span class="type">static</span> <span class="keyword">struct</span> <span class="title class_">irq_chip</span> gic_chip = {</span><br><span class="line"> .name = <span class="string">"GIC"</span>,</span><br><span class="line"> .irq_mask = gic_mask_irq,</span><br><span class="line"> .irq_unmask = gic_unmask_irq,</span><br><span class="line"> .irq_eoi = gic_eoi_irq,</span><br><span class="line"> .irq_set_type = gic_set_type,</span><br><span class="line"> .irq_retrigger = gic_retrigger,</span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_SMP</span></span><br><span class="line"> .irq_set_affinity = gic_set_affinity,</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"> .irq_set_wake = gic_set_wake,</span><br><span class="line">};</span><br></pre></td></tr></table></figure>
<h3 id="1-3-Linux-中断处理流程"><a href="#1-3-Linux-中断处理流程" class="headerlink" title="1.3 Linux 中断处理流程"></a>1.3 Linux 中断处理流程</h3><p>从代码上看 Linux 中断的处理流程大概是这样的：</p>
<p><img src="int_handle_flow.png" alt="Linux 中断处理基本流程 "></p>
<p>从处理流程上看，对于 gic 的每个中断源，Linux 系统分配一个 irq_desc 数据结构与之对应。irq_desc 结构中有两个中断处理函数 <code>desc->handle_irq()</code> 和 <code>desc->action->handler()</code>，这两个函数代表中断处理的两个层级：</p>
<ul>
<li><p><code>desc->handle_irq()</code>。第一层次的中断处理函数，这个是系统在初始化时根据中断源的特征统一分配的，不同类型的中断源的 gic 操作是不一样的，把这些通用 gic 操作提取出来就是第一层次的操作函数。具体实现包括：</p>
<ul>
<li><code>handle_fasteoi_irq()</code></li>
<li><code>handle_simple_irq()</code></li>
<li><code>handle_edge_irq()</code></li>
<li><code>handle_level_irq()</code></li>
<li><code>handle_percpu_irq()</code></li>
<li><code>handle_percpu_devid_irq()</code></li>
</ul>
</li>
<li><p><code>desc->action->handler()</code> 第二层次的中断处理函数，由用户注册实现具体设备的驱动服务程序，都是和 GIC 操作无关的代码。同时一个中断源可以多个设备共享，所以一个 desc 可以挂载多个 action，由链表结构组织起来。</p>
</li>
</ul>
<p><img src="int_handler_action.png" alt="Linux 中断处理层级 "></p>
<h3 id="1-4-中断服务注册"><a href="#1-4-中断服务注册" class="headerlink" title="1.4 中断服务注册"></a>1.4 中断服务注册</h3><p>从上一节的中断二层结构中可以看到第二层的中断处理函数 desc->action->handler 是由用户来注册的，下面我们来分析具体注册过程：</p>
<ul>
<li>kernel/irq/manage.c:</li>
<li><code>request_irq()</code> -> <code>request_threaded_irq()</code> -> <code>__setup_irq()</code></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 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class="line">392</span><br><span class="line">393</span><br><span class="line">394</span><br><span class="line">395</span><br><span class="line">396</span><br><span class="line">397</span><br><span class="line">398</span><br><span class="line">399</span><br><span class="line">400</span><br><span class="line">401</span><br><span class="line">402</span><br><span class="line">403</span><br><span class="line">404</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">int</span> __must_check</span></span><br><span class="line"><span class="function"><span class="title">request_irq</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> irq, <span class="type">irq_handler_t</span> handler, <span class="type">unsigned</span> <span class="type">long</span> flags,</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="type">const</span> <span class="type">char</span> *name, <span class="type">void</span> *dev)</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">request_threaded_irq</span>(irq, handler, <span class="literal">NULL</span>, flags, name, dev);</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">request_threaded_irq</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> irq, <span class="type">irq_handler_t</span> handler,</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="type">irq_handler_t</span> thread_fn, <span class="type">unsigned</span> <span class="type">long</span> irqflags,</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="type">const</span> <span class="type">char</span> *devname, <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_">irqaction</span> *action;</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">irq_desc</span> *desc;</span><br><span class="line"> <span class="type">int</span> retval;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Sanity-check: shared interrupts must pass in a real dev-ID,</span></span><br><span class="line"><span class="comment"> * otherwise we'll have trouble later trying to figure out</span></span><br><span class="line"><span class="comment"> * which interrupt is which (messes up the interrupt freeing</span></span><br><span class="line"><span class="comment"> * logic etc).</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> ((irqflags & IRQF_SHARED) && !dev_id)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (1) 根据中断号找到对应的 desc 结构</span></span><br><span class="line"> desc = <span class="built_in">irq_to_desc</span>(irq);</span><br><span class="line"> <span class="keyword">if</span> (!desc)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">irq_settings_can_request</span>(desc) ||</span><br><span class="line"> <span class="built_in">WARN_ON</span>(<span class="built_in">irq_settings_is_per_cpu_devid</span>(desc)))</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (2) 如果 action->handler 为空，那么用户是想创建一个线程化中断</span></span><br><span class="line"> <span class="comment">// 将线程化中断的 action->handler 初始化为 irq_default_primary_handler()</span></span><br><span class="line"> <span class="comment">// irq_default_primary_handler() 非常简单，只是返回一个 IRQ_WAKE_THREAD 值</span></span><br><span class="line"> <span class="keyword">if</span> (!handler) {</span><br><span class="line"> <span class="keyword">if</span> (!thread_fn)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"> handler = irq_default_primary_handler;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (3) 分配新的 action 数据结构</span></span><br><span class="line"> action = <span class="built_in">kzalloc</span>(<span class="built_in">sizeof</span>(<span class="keyword">struct</span> irqaction), GFP_KERNEL);</span><br><span class="line"> <span class="keyword">if</span> (!action)</span><br><span class="line"> <span class="keyword">return</span> -ENOMEM;</span><br><span class="line"></span><br><span class="line"> action->handler = handler;</span><br><span class="line"> action->thread_fn = thread_fn;</span><br><span class="line"> action->flags = irqflags;</span><br><span class="line"> action->name = devname;</span><br><span class="line"> action->dev_id = dev_id;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">chip_bus_lock</span>(desc);</span><br><span class="line"> <span class="comment">// (4) 将新的 action 结构安装到 desc 中</span></span><br><span class="line"> retval = __setup_irq(irq, desc, action);</span><br><span class="line"> <span class="built_in">chip_bus_sync_unlock</span>(desc);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (retval)</span><br><span class="line"> <span class="built_in">kfree</span>(action);</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_DEBUG_SHIRQ_FIXME</span></span><br><span class="line"> <span class="keyword">if</span> (!retval && (irqflags & IRQF_SHARED)) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * It's a shared IRQ -- the driver ought to be prepared for it</span></span><br><span class="line"><span class="comment"> * to happen immediately, so let's make sure....</span></span><br><span class="line"><span class="comment"> * We disable the irq to make sure that a 'real' IRQ doesn't</span></span><br><span class="line"><span class="comment"> * run in parallel with our fake.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">disable_irq</span>(irq);</span><br><span class="line"> <span class="built_in">local_irq_save</span>(flags);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">handler</span>(irq, dev_id);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">local_irq_restore</span>(flags);</span><br><span class="line"> <span class="built_in">enable_irq</span>(irq);</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="keyword">return</span> retval;</span><br><span class="line">}</span><br><span class="line">|| →</span><br><span class="line"><span class="type">static</span> <span class="type">int</span></span><br><span class="line">__setup_irq(<span class="type">unsigned</span> <span class="type">int</span> irq, <span class="keyword">struct</span> irq_desc *desc, <span class="keyword">struct</span> irqaction *<span class="keyword">new</span>)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">irqaction</span> *old, **old_ptr;</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags, thread_mask = <span class="number">0</span>;</span><br><span class="line"> <span class="type">int</span> ret, nested, shared = <span class="number">0</span>;</span><br><span class="line"> <span class="type">cpumask_var_t</span> mask;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!desc)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (desc->irq_data.chip == &no_irq_chip)</span><br><span class="line"> <span class="keyword">return</span> -ENOSYS;</span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">try_module_get</span>(desc->owner))</span><br><span class="line"> <span class="keyword">return</span> -ENODEV;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Check whether the interrupt nests into another interrupt</span></span><br><span class="line"><span class="comment"> * thread.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> nested = <span class="built_in">irq_settings_is_nested_thread</span>(desc);</span><br><span class="line"> <span class="comment">// (4.1) 判断中断是否是支持嵌套</span></span><br><span class="line"> <span class="keyword">if</span> (nested) {</span><br><span class="line"> <span class="keyword">if</span> (!<span class="keyword">new</span>->thread_fn) {</span><br><span class="line"> ret = -EINVAL;</span><br><span class="line"> <span class="keyword">goto</span> out_mput;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Replace the primary handler which was provided from</span></span><br><span class="line"><span class="comment"> * the driver for non nested interrupt handling by the</span></span><br><span class="line"><span class="comment"> * dummy function which warns when called.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">new</span>->handler = irq_nested_primary_handler;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// (4.2) 判断中断是否可以被线程化</span></span><br><span class="line"> <span class="comment">// 如果中断没有设置 _IRQ_NOTHREAD 标志 & 强制中断线程化标志被设置 (force_irqthreads=1)</span></span><br><span class="line"> <span class="comment">// 强制把中断线程化：</span></span><br><span class="line"> <span class="comment">// new->thread_fn = new->handler;new->handler = irq_default_primary_handler;</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">irq_settings_can_thread</span>(desc))</span><br><span class="line"> <span class="built_in">irq_setup_forced_threading</span>(<span class="keyword">new</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"> * Create a handler thread when a thread function is supplied</span></span><br><span class="line"><span class="comment"> * and the interrupt does not nest into another interrupt</span></span><br><span class="line"><span class="comment"> * thread.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// (4.3) 如果是线程化中断，创建线程化中断对应的线程</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->thread_fn && !nested) {</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">task_struct</span> *t;</span><br><span class="line"> <span class="type">static</span> <span class="type">const</span> <span class="keyword">struct</span> <span class="title class_">sched_param</span> param = {</span><br><span class="line"> .sched_priority = MAX_USER_RT_PRIO/<span class="number">2</span>,</span><br><span class="line"> };</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 创建线程</span></span><br><span class="line"> t = <span class="built_in">kthread_create</span>(irq_thread, <span class="keyword">new</span>, <span class="string">"irq/%d-%s"</span>, irq,</span><br><span class="line"> <span class="keyword">new</span>->name);</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">IS_ERR</span>(t)) {</span><br><span class="line"> ret = <span class="built_in">PTR_ERR</span>(t);</span><br><span class="line"> <span class="keyword">goto</span> out_mput;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="built_in">sched_setscheduler_nocheck</span>(t, SCHED_FIFO, &param);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * We keep the reference to the task struct even if</span></span><br><span class="line"><span class="comment"> * the thread dies to avoid that the interrupt code</span></span><br><span class="line"><span class="comment"> * references an already freed task_struct.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="built_in">get_task_struct</span>(t);</span><br><span class="line"> <span class="comment">// 赋值给 ->thread 成员</span></span><br><span class="line"> <span class="keyword">new</span>->thread = t;</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Tell the thread to set its affinity. This is</span></span><br><span class="line"><span class="comment"> * important for shared interrupt handlers as we do</span></span><br><span class="line"><span class="comment"> * not invoke setup_affinity() for the secondary</span></span><br><span class="line"><span class="comment"> * handlers as everything is already set up. Even for</span></span><br><span class="line"><span class="comment"> * interrupts marked with IRQF_NO_BALANCE this is</span></span><br><span class="line"><span class="comment"> * correct as we want the thread to move to the cpu(s)</span></span><br><span class="line"><span class="comment"> * on which the requesting code placed the interrupt.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="built_in">set_bit</span>(IRQTF_AFFINITY, &<span class="keyword">new</span>->thread_flags);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">alloc_cpumask_var</span>(&mask, GFP_KERNEL)) {</span><br><span class="line"> ret = -ENOMEM;</span><br><span class="line"> <span class="keyword">goto</span> out_thread;</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"> * Drivers are often written to work w/o knowledge about the</span></span><br><span class="line"><span class="comment"> * underlying irq chip implementation, so a request for a</span></span><br><span class="line"><span class="comment"> * threaded irq without a primary hard irq context handler</span></span><br><span class="line"><span class="comment"> * requires the ONESHOT flag to be set. Some irq chips like</span></span><br><span class="line"><span class="comment"> * MSI based interrupts are per se one shot safe. Check the</span></span><br><span class="line"><span class="comment"> * chip flags, so we can avoid the unmask dance at the end of</span></span><br><span class="line"><span class="comment"> * the threaded handler for those.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)</span><br><span class="line"> <span class="keyword">new</span>->flags &= ~IRQF_ONESHOT;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * The following block of code has to be executed atomically</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// (4.4) 找到最后一个 action 结构</span></span><br><span class="line"> <span class="built_in">raw_spin_lock_irqsave</span>(&desc->lock, flags);</span><br><span class="line"> old_ptr = &desc->action;</span><br><span class="line"> old = *old_ptr;</span><br><span class="line"> <span class="keyword">if</span> (old) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Can't share interrupts unless both agree to and are</span></span><br><span class="line"><span class="comment"> * the same type (level, edge, polarity). So both flag</span></span><br><span class="line"><span class="comment"> * fields must have IRQF_SHARED set and the bits which</span></span><br><span class="line"><span class="comment"> * set the trigger type must match. Also all must</span></span><br><span class="line"><span class="comment"> * agree on ONESHOT.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (!((old->flags & <span class="keyword">new</span>->flags) & IRQF_SHARED) ||</span><br><span class="line"> ((old->flags ^ <span class="keyword">new</span>->flags) & IRQF_TRIGGER_MASK) ||</span><br><span class="line"> ((old->flags ^ <span class="keyword">new</span>->flags) & IRQF_ONESHOT))</span><br><span class="line"> <span class="keyword">goto</span> mismatch;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* All handlers must agree on per-cpuness */</span></span><br><span class="line"> <span class="keyword">if</span> ((old->flags & IRQF_PERCPU) !=</span><br><span class="line"> (<span class="keyword">new</span>->flags & IRQF_PERCPU))</span><br><span class="line"> <span class="keyword">goto</span> mismatch;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* add new interrupt at end of irq queue */</span></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Or all existing action->thread_mask bits,</span></span><br><span class="line"><span class="comment"> * so we can find the next zero bit for this</span></span><br><span class="line"><span class="comment"> * new action.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> thread_mask |= old->thread_mask;</span><br><span class="line"> old_ptr = &old->next;</span><br><span class="line"> old = *old_ptr;</span><br><span class="line"> } <span class="keyword">while</span> (old);</span><br><span class="line"> <span class="comment">// 如果有多个 action，共享标志设为 1</span></span><br><span class="line"> shared = <span class="number">1</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"> * Setup the thread mask for this irqaction for ONESHOT. For</span></span><br><span class="line"><span class="comment"> * !ONESHOT irqs the thread mask is 0 so we can avoid a</span></span><br><span class="line"><span class="comment"> * conditional in irq_wake_thread().</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->flags & IRQF_ONESHOT) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Unlikely to have 32 resp 64 irqs sharing one line,</span></span><br><span class="line"><span class="comment"> * but who knows.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">if</span> (thread_mask == ~<span class="number">0UL</span>) {</span><br><span class="line"> ret = -EBUSY;</span><br><span class="line"> <span class="keyword">goto</span> out_mask;</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * The thread_mask for the action is or'ed to</span></span><br><span class="line"><span class="comment"> * desc->thread_active to indicate that the</span></span><br><span class="line"><span class="comment"> * IRQF_ONESHOT thread handler has been woken, but not</span></span><br><span class="line"><span class="comment"> * yet finished. The bit is cleared when a thread</span></span><br><span class="line"><span class="comment"> * completes. When all threads of a shared interrupt</span></span><br><span class="line"><span class="comment"> * line have completed desc->threads_active becomes</span></span><br><span class="line"><span class="comment"> * zero and the interrupt line is unmasked. See</span></span><br><span class="line"><span class="comment"> * handle.c:irq_wake_thread() for further information.</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * If no thread is woken by primary (hard irq context)</span></span><br><span class="line"><span class="comment"> * interrupt handlers, then desc->threads_active is</span></span><br><span class="line"><span class="comment"> * also checked for zero to unmask the irq line in the</span></span><br><span class="line"><span class="comment"> * affected hard irq flow handlers</span></span><br><span class="line"><span class="comment"> * (handle_[fasteoi|level]_irq).</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * The new action gets the first zero bit of</span></span><br><span class="line"><span class="comment"> * thread_mask assigned. See the loop above which or's</span></span><br><span class="line"><span class="comment"> * all existing action->thread_mask bits.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="keyword">new</span>->thread_mask = <span class="number">1</span> << <span class="built_in">ffz</span>(thread_mask);</span><br><span class="line"></span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (<span class="keyword">new</span>->handler == irq_default_primary_handler &&</span><br><span class="line"> !(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) {</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * The interrupt was requested with handler = NULL, so</span></span><br><span class="line"><span class="comment"> * we use the default primary handler for it. But it</span></span><br><span class="line"><span class="comment"> * does not have the oneshot flag set. In combination</span></span><br><span class="line"><span class="comment"> * with level interrupts this is deadly, because the</span></span><br><span class="line"><span class="comment"> * default primary handler just wakes the thread, then</span></span><br><span class="line"><span class="comment"> * the irq lines is reenabled, but the device still</span></span><br><span class="line"><span class="comment"> * has the level irq asserted. Rinse and repeat....</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> * While this works for edge type interrupts, we play</span></span><br><span class="line"><span class="comment"> * it safe and reject unconditionally because we can't</span></span><br><span class="line"><span class="comment"> * say for sure which type this interrupt really</span></span><br><span class="line"><span class="comment"> * has. The type flags are unreliable as the</span></span><br><span class="line"><span class="comment"> * underlying chip implementation can override them.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="built_in">pr_err</span>(<span class="string">"Threaded irq requested with handler=NULL and !ONESHOT for irq %d\n"</span>,</span><br><span class="line"> irq);</span><br><span class="line"> ret = -EINVAL;</span><br><span class="line"> <span class="keyword">goto</span> out_mask;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (4.5) 如果是第一个 action，做一些初始化工作</span></span><br><span class="line"> <span class="keyword">if</span> (!shared) {</span><br><span class="line"> ret = <span class="built_in">irq_request_resources</span>(desc);</span><br><span class="line"> <span class="keyword">if</span> (ret) {</span><br><span class="line"> <span class="built_in">pr_err</span>(<span class="string">"Failed to request resources for %s (irq %d) on irqchip %s\n"</span>,</span><br><span class="line"> <span class="keyword">new</span>->name, irq, desc->irq_data.chip->name);</span><br><span class="line"> <span class="keyword">goto</span> out_mask;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="built_in">init_waitqueue_head</span>(&desc->wait_for_threads);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Setup the type (level, edge polarity) if configured: */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->flags & IRQF_TRIGGER_MASK) {</span><br><span class="line"> ret = __irq_set_trigger(desc, irq,</span><br><span class="line"> <span class="keyword">new</span>->flags & IRQF_TRIGGER_MASK);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (ret)</span><br><span class="line"> <span class="keyword">goto</span> out_mask;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> desc->istate &= ~(IRQS_AUTODETECT | IRQS_SPURIOUS_DISABLED | \</span><br><span class="line"> IRQS_ONESHOT | IRQS_WAITING);</span><br><span class="line"> <span class="built_in">irqd_clear</span>(&desc->irq_data, IRQD_IRQ_INPROGRESS);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->flags & IRQF_PERCPU) {</span><br><span class="line"> <span class="built_in">irqd_set</span>(&desc->irq_data, IRQD_PER_CPU);</span><br><span class="line"> <span class="built_in">irq_settings_set_per_cpu</span>(desc);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->flags & IRQF_ONESHOT)</span><br><span class="line"> desc->istate |= IRQS_ONESHOT;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">irq_settings_can_autoenable</span>(desc))</span><br><span class="line"> <span class="built_in">irq_startup</span>(desc, <span class="literal">true</span>);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> <span class="comment">/* Undo nested disables: */</span></span><br><span class="line"> desc->depth = <span class="number">1</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Exclude IRQ from balancing if requested */</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->flags & IRQF_NOBALANCING) {</span><br><span class="line"> <span class="built_in">irq_settings_set_no_balancing</span>(desc);</span><br><span class="line"> <span class="built_in">irqd_set</span>(&desc->irq_data, IRQD_NO_BALANCING);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 设置中断亲和力</span></span><br><span class="line"> <span class="comment">/* Set default affinity mask once everything is setup */</span></span><br><span class="line"> <span class="built_in">setup_affinity</span>(irq, desc, mask);</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (<span class="keyword">new</span>->flags & IRQF_TRIGGER_MASK) {</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">int</span> nmsk = <span class="keyword">new</span>->flags & IRQF_TRIGGER_MASK;</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">int</span> omsk = <span class="built_in">irq_settings_get_trigger_mask</span>(desc);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (nmsk != omsk)</span><br><span class="line"> <span class="comment">/* hope the handler works with current trigger mode */</span></span><br><span class="line"> <span class="built_in">pr_warning</span>(<span class="string">"irq %d uses trigger mode %u; requested %u\n"</span>,</span><br><span class="line"> irq, nmsk, omsk);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (4.6) 将新的 action 插入到 desc 链表中</span></span><br><span class="line"> <span class="keyword">new</span>->irq = irq;</span><br><span class="line"> *old_ptr = <span class="keyword">new</span>;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">irq_pm_install_action</span>(desc, <span class="keyword">new</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Reset broken irq detection when installing new handler */</span></span><br><span class="line"> desc->irq_count = <span class="number">0</span>;</span><br><span class="line"> desc->irqs_unhandled = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Check whether we disabled the irq via the spurious handler</span></span><br><span class="line"><span class="comment"> * before. Reenable it and give it another chance.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// (4.7) 如果中断之前被虚假 disable 了，重新 enable 中断</span></span><br><span class="line"> <span class="keyword">if</span> (shared && (desc->istate & IRQS_SPURIOUS_DISABLED)) {</span><br><span class="line"> desc->istate &= ~IRQS_SPURIOUS_DISABLED;</span><br><span class="line"> __enable_irq(desc, irq);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="built_in">raw_spin_unlock_irqrestore</span>(&desc->lock, flags);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Strictly no need to wake it up, but hung_task complains</span></span><br><span class="line"><span class="comment"> * when no hard interrupt wakes the thread up.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// (4.8) 唤醒线程化中断对应的线程</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->thread)</span><br><span class="line"> <span class="built_in">wake_up_process</span>(<span class="keyword">new</span>->thread);</span><br><span class="line"></span><br><span class="line"> <span class="built_in">register_irq_proc</span>(irq, desc);</span><br><span class="line"> <span class="keyword">new</span>->dir = <span class="literal">NULL</span>;</span><br><span class="line"> <span class="built_in">register_handler_proc</span>(irq, <span class="keyword">new</span>);</span><br><span class="line"> <span class="built_in">free_cpumask_var</span>(mask);</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">mismatch:</span><br><span class="line"> <span class="keyword">if</span> (!(<span class="keyword">new</span>->flags & IRQF_PROBE_SHARED)) {</span><br><span class="line"> <span class="built_in">pr_err</span>(<span class="string">"Flags mismatch irq %d. %08x (%s) vs. %08x (%s)\n"</span>,</span><br><span class="line"> irq, <span class="keyword">new</span>->flags, <span class="keyword">new</span>->name, old->flags, old->name);</span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_DEBUG_SHIRQ</span></span><br><span class="line"> <span class="built_in">dump_stack</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"> ret = -EBUSY;</span><br><span class="line"></span><br><span class="line">out_mask:</span><br><span class="line"> <span class="built_in">raw_spin_unlock_irqrestore</span>(&desc->lock, flags);</span><br><span class="line"> <span class="built_in">free_cpumask_var</span>(mask);</span><br><span class="line"></span><br><span class="line">out_thread:</span><br><span class="line"> <span class="keyword">if</span> (<span class="keyword">new</span>->thread) {</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">task_struct</span> *t = <span class="keyword">new</span>->thread;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">new</span>->thread = <span class="literal">NULL</span>;</span><br><span class="line"> <span class="built_in">kthread_stop</span>(t);</span><br><span class="line"> <span class="built_in">put_task_struct</span>(t);</span><br><span class="line"> }</span><br><span class="line">out_mput:</span><br><span class="line"> <span class="built_in">module_put</span>(desc->owner);</span><br><span class="line"> <span class="keyword">return</span> ret;</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h3 id="1-5-中断线程化"><a href="#1-5-中断线程化" class="headerlink" title="1.5 中断线程化"></a>1.5 中断线程化</h3><p>从上一节可以看到，使用 <code>request_irq()</code> 注册的是传统中断，而直接使用 <code>request_threaded_irq()</code> 注册的是线程化中断。线程化中断的主要目的是把中断上下文的任务迁移到线程中，减少系统关中断的时间，增强系统的实时性。</p>
<p>中断对应的线程命名规则为：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">t = <span class="built_in">kthread_create</span>(irq_thread, <span class="keyword">new</span>, <span class="string">"irq/%d-%s"</span>, irq, <span class="keyword">new</span>->name);</span><br></pre></td></tr></table></figure>
<p>我们通过 ps 命令查看系统中的中断线程，注意这些线程是实时线程 SCHED_FIFO：</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></pre></td><td class="code"><pre><span class="line">root@:/ <span class="meta"># ps | grep <span class="string">"irq/"</span></span></span><br><span class="line">root <span class="number">171</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> irq_thread <span class="number">0000000000</span> S irq/<span class="number">389</span>-charger</span><br><span class="line">root <span class="number">239</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> irq_thread <span class="number">0000000000</span> S irq/<span class="number">296</span>-PS_int-</span><br><span class="line">root <span class="number">247</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> irq_thread <span class="number">0000000000</span> S irq/<span class="number">297</span><span class="number">-1124000</span></span><br><span class="line">root <span class="number">1415</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> irq_thread <span class="number">0000000000</span> S irq/<span class="number">293</span>-goodix_</span><br><span class="line">root@a0255:/ #</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<p>线程化中断的创建和处理任务流程如下：</p>
<p><img src="int_thread_irq.png" alt="Linux 线程化中断 "></p>
<p>线程和 action 是一一对应的，即用户注册一个中断处理程序对应一个中断线程。</p>
<h3 id="1-6-外设中断打开-关闭"><a href="#1-6-外设中断打开-关闭" class="headerlink" title="1.6 外设中断打开 / 关闭"></a>1.6 外设中断打开 / 关闭</h3><p>前面的章节讲述了本地 CPU 全局中断的 enable/disable。如果要操作单个中断源的 enable/disable，使用 <code>enable_irq()</code>/<code>disable_irq()</code> 函数。最后调用主要是 GIC chip 相关的函数：</p>
<ul>
<li>kernel/irq/manage.c:</li>
<li><code>enable_irq()</code> -> <code>__enable_irq()</code> -> <code>irq_enable()</code></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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">enable_irq</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> irq)</span></span></span><br><span class="line"><span class="function"></span>{</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_">irq_desc</span> *desc = <span class="built_in">irq_get_desc_buslock</span>(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!desc)</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">WARN</span>(!desc->irq_data.chip,</span><br><span class="line"> KERN_ERR <span class="string">"enable_irq before setup/request_irq: irq %u\n"</span>, irq))</span><br><span class="line"> <span class="keyword">goto</span> out;</span><br><span class="line"></span><br><span class="line"> __enable_irq(desc, irq);</span><br><span class="line">out:</span><br><span class="line"> <span class="built_in">irq_put_desc_busunlock</span>(desc, flags);</span><br><span class="line">}</span><br><span class="line">| →</span><br><span class="line"><span class="type">void</span> __enable_irq(<span class="keyword">struct</span> irq_desc *desc, <span class="type">unsigned</span> <span class="type">int</span> irq)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">switch</span> (desc->depth) {</span><br><span class="line"> <span class="keyword">case</span> <span class="number">0</span>:</span><br><span class="line"> err_out:</span><br><span class="line"> <span class="built_in">WARN</span>(<span class="number">1</span>, KERN_WARNING <span class="string">"Unbalanced enable for IRQ %d\n"</span>, irq);</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> <span class="keyword">case</span> <span class="number">1</span>: {</span><br><span class="line"> <span class="keyword">if</span> (desc->istate & IRQS_SUSPENDED)</span><br><span class="line"> <span class="keyword">goto</span> err_out;</span><br><span class="line"> <span class="comment">/* Prevent probing on this irq: */</span></span><br><span class="line"> <span class="built_in">irq_settings_set_noprobe</span>(desc);</span><br><span class="line"> <span class="built_in">irq_enable</span>(desc);</span><br><span class="line"> <span class="built_in">check_irq_resend</span>(desc, irq);</span><br><span class="line"> <span class="comment">/* fall-through */</span></span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">default</span>:</span><br><span class="line"> desc->depth--;</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">irq_enable</span><span class="params">(<span class="keyword">struct</span> irq_desc *desc)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="comment">// 操作 GIC chip 对应的函数</span></span><br><span class="line"> <span class="built_in">irq_state_clr_disabled</span>(desc);</span><br><span class="line"> <span class="keyword">if</span> (desc->irq_data.chip->irq_enable)</span><br><span class="line"> desc->irq_data.chip-><span class="built_in">irq_enable</span>(&desc->irq_data);</span><br><span class="line"> <span class="keyword">else</span></span><br><span class="line"> desc->irq_data.chip-><span class="built_in">irq_unmask</span>(&desc->irq_data);</span><br><span class="line"> <span class="built_in">irq_state_clr_masked</span>(desc);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li>kernel/irq/manage.c:</li>
<li><code>enable_irq()</code> -> <code>__enable_irq()</code> -> <code>irq_enable()</code></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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">disable_irq</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> irq)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">if</span> (!__disable_irq_nosync(irq))</span><br><span class="line"> <span class="built_in">synchronize_irq</span>(irq);</span><br><span class="line">}</span><br><span class="line">| →</span><br><span class="line"><span class="type">static</span> <span class="type">int</span> __disable_irq_nosync(<span class="type">unsigned</span> <span class="type">int</span> irq)</span><br><span class="line">{</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_">irq_desc</span> *desc = <span class="built_in">irq_get_desc_buslock</span>(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!desc)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"> __disable_irq(desc, irq);</span><br><span class="line"> <span class="built_in">irq_put_desc_busunlock</span>(desc, flags);</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="type">void</span> __disable_irq(<span class="keyword">struct</span> irq_desc *desc, <span class="type">unsigned</span> <span class="type">int</span> irq)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">if</span> (!desc->depth++)</span><br><span class="line"> <span class="built_in">irq_disable</span>(desc);</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">irq_disable</span><span class="params">(<span class="keyword">struct</span> irq_desc *desc)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="comment">// 操作 GIC chip 对应的函数</span></span><br><span class="line"> <span class="built_in">irq_state_set_disabled</span>(desc);</span><br><span class="line"> <span class="keyword">if</span> (desc->irq_data.chip->irq_disable) {</span><br><span class="line"> desc->irq_data.chip-><span class="built_in">irq_disable</span>(&desc->irq_data);</span><br><span class="line"> <span class="built_in">irq_state_set_masked</span>(desc);</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">synchronize_irq</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> irq)</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_">irq_desc</span> *desc = <span class="built_in">irq_to_desc</span>(irq);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (desc) {</span><br><span class="line"> __synchronize_hardirq(desc);</span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * We made sure that no hardirq handler is</span></span><br><span class="line"><span class="comment"> * running. Now verify that no threaded handlers are</span></span><br><span class="line"><span class="comment"> * active.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="comment">// 如果是线程化中断，需要等到线程执行完成</span></span><br><span class="line"> <span class="built_in">wait_event</span>(desc->wait_for_threads,</span><br><span class="line"> !<span class="built_in">atomic_read</span>(&desc->threads_active));</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h3 id="1-7-中断亲和力"><a href="#1-7-中断亲和力" class="headerlink" title="1.7 中断亲和力"></a>1.7 中断亲和力</h3><p>同样基于 GIC chip 提供的能力，我们能配置中断源对 CPU 的亲和力。</p>
<ul>
<li>kernel/irq/manage.c:</li>
<li><code>enable_irq()</code> -> <code>__enable_irq()</code> -> <code>irq_enable()</code></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></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">int</span></span></span><br><span class="line"><span class="function"><span class="title">irq_set_affinity</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> irq, <span class="type">const</span> <span class="keyword">struct</span> cpumask *cpumask)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">return</span> __irq_set_affinity(irq, cpumask, <span class="literal">false</span>);</span><br><span class="line">}</span><br><span class="line">| →</span><br><span class="line"><span class="type">int</span> __irq_set_affinity(<span class="type">unsigned</span> <span class="type">int</span> irq, <span class="type">const</span> <span class="keyword">struct</span> cpumask *mask, <span class="type">bool</span> force)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">irq_desc</span> *desc = <span class="built_in">irq_to_desc</span>(irq);</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"> <span class="type">int</span> ret;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!desc)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">raw_spin_lock_irqsave</span>(&desc->lock, flags);</span><br><span class="line"> ret = <span class="built_in">irq_set_affinity_locked</span>(<span class="built_in">irq_desc_get_irq_data</span>(desc), mask, force);</span><br><span class="line"> <span class="built_in">raw_spin_unlock_irqrestore</span>(&desc->lock, flags);</span><br><span class="line"> <span class="keyword">return</span> ret;</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">irq_set_affinity_locked</span><span class="params">(<span class="keyword">struct</span> irq_data *data, <span class="type">const</span> <span class="keyword">struct</span> cpumask *mask,</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="type">bool</span> force)</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_">irq_chip</span> *chip = <span class="built_in">irq_data_get_irq_chip</span>(data);</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">irq_desc</span> *desc = <span class="built_in">irq_data_to_desc</span>(data);</span><br><span class="line"> <span class="type">int</span> ret = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!chip || !chip->irq_set_affinity)</span><br><span class="line"> <span class="keyword">return</span> -EINVAL;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">irq_can_move_pcntxt</span>(data)) {</span><br><span class="line"> ret = <span class="built_in">irq_do_set_affinity</span>(data, mask, force);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="built_in">irqd_set_move_pending</span>(data);</span><br><span class="line"> <span class="built_in">irq_copy_pending</span>(desc, mask);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (desc->affinity_notify) {</span><br><span class="line"> <span class="built_in">kref_get</span>(&desc->affinity_notify->kref);</span><br><span class="line"> <span class="built_in">schedule_work</span>(&desc->affinity_notify->work);</span><br><span class="line"> }</span><br><span class="line"> <span class="built_in">irqd_set</span>(data, IRQD_AFFINITY_SET);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ret;</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">irq_do_set_affinity</span><span class="params">(<span class="keyword">struct</span> irq_data *data, <span class="type">const</span> <span class="keyword">struct</span> cpumask *mask,</span></span></span><br><span class="line"><span class="params"><span class="function"> <span class="type">bool</span> force)</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_">irq_desc</span> *desc = <span class="built_in">irq_data_to_desc</span>(data);</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">irq_chip</span> *chip = <span class="built_in">irq_data_get_irq_chip</span>(data);</span><br><span class="line"> <span class="type">int</span> ret;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// 操作 GIC chip 对应的函数</span></span><br><span class="line"> ret = chip-><span class="built_in">irq_set_affinity</span>(data, mask, force);</span><br><span class="line"> <span class="keyword">switch</span> (ret) {</span><br><span class="line"> <span class="keyword">case</span> IRQ_SET_MASK_OK:</span><br><span class="line"> <span class="keyword">case</span> IRQ_SET_MASK_OK_DONE:</span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_MTK_IRQ_NEW_DESIGN</span></span><br><span class="line"> <span class="built_in">update_affinity_settings</span>(desc, mask, <span class="literal">true</span>);</span><br><span class="line"><span class="meta">#<span class="keyword">else</span></span></span><br><span class="line"> <span class="built_in">cpumask_copy</span>(data->affinity, mask);</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"> <span class="keyword">case</span> IRQ_SET_MASK_OK_NOCOPY:</span><br><span class="line"> <span class="built_in">irq_set_thread_affinity</span>(desc);</span><br><span class="line"> ret = <span class="number">0</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ret;</span><br><span class="line">}</span><br><span class="line"></span><br></pre></td></tr></table></figure>
<h2 id="2-Linux-中断下半部"><a href="#2-Linux-中断下半部" class="headerlink" title="2. Linux 中断下半部"></a>2. Linux 中断下半部</h2><p>接下来就是大名鼎鼎的中断下半部了，包括：softirq、tasklet、workqueue。中断下半部的主要目的就是减少系统关中断的时间，把关键代码放在中断中做，大部分处理代码放到不用关中断的空间去做。</p>
<p>上面有最激进的方法中断线程化，但是大部分时候还是需要用到中断上、下半部的方法。</p>
<p>workqueue 在另外文章中已经有详细解析，本处只解析 softirq、tasklet。</p>
<h3 id="2-1-preempt-count"><a href="#2-1-preempt-count" class="headerlink" title="2.1 preempt_count"></a>2.1 preempt_count</h3><figure class="highlight livescript"><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></pre></td><td class="code"><pre><span class="line"><span class="keyword">static</span> __always_inline int preempt_count(<span class="literal">void</span>)</span><br><span class="line">{</span><br><span class="line"> <span class="keyword">return</span> current_thread_info<span class="function"><span class="params">()</span>-></span>preempt_count; <span class="comment">/* 0 => preemptable, <0 => bug */</span></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>开始之前先了解一下 preempt_count 这个背景知识，preempt_count 是 thread_info 结构中的一个字段，用来表示当前进程能否被抢占。</p>
<p>所谓的抢占：是指在进程在内核空间运行，如果主动不释放 CPU，在时间片用完或者高优先级任务就绪的情况下，会被强行剥夺掉 CPU 的使用权。</p>
<p>但是进程可能在做一些关键操作，不能被抢占，被抢占后系统会出错。所以 Linux 设计了 preempt_count 字段，=0 可以被抢占，>0 不能被抢占。</p>
<p>进程在中断返回内核态时，做是否可抢占的检查：</p>
<ul>
<li>arch/arm64/kernel/entry.s:</li>
<li><code>el1_irq()</code> -> <code>__enable_irq()</code> -> <code>irq_enable()</code></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></pre></td><td class="code"><pre><span class="line"> .align <span class="number">6</span></span><br><span class="line">el1_irq:</span><br><span class="line"> kernel_entry <span class="number">1</span></span><br><span class="line"> enable_dbg</span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_TRACE_IRQFLAGS</span></span><br><span class="line"> bl trace_hardirqs_off</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">ifdef</span> CONFIG_MTPROF</span></span><br><span class="line"> bl MT_trace_hardirqs_off</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"> irq_handler</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_PREEMPT</span></span><br><span class="line"> get_thread_info tsk</span><br><span class="line"> ldr w24, [tsk, #TI_PREEMPT] <span class="comment">// get preempt count</span></span><br><span class="line"> <span class="comment">// (1) 如果 preempt_count!=0，不进行可抢占判断</span></span><br><span class="line"> cbnz w24, <span class="number">1</span>f <span class="comment">// preempt count != 0</span></span><br><span class="line"> ldr x0, [tsk, #TI_FLAGS] <span class="comment">// get flags</span></span><br><span class="line"> <span class="comment">// (2) 如果 preempt_count==0 & TIF_NEED_RESCHED 被置位</span></span><br><span class="line"> <span class="comment">// 进行调度</span></span><br><span class="line"> tbz x0, #TIF_NEED_RESCHED, <span class="number">1</span>f <span class="comment">// needs rescheduling?</span></span><br><span class="line"> bl el1_preempt</span><br><span class="line"><span class="number">1</span>:</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">ifdef</span> CONFIG_MTPROF</span></span><br><span class="line"> bl MT_trace_hardirqs_on</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">ifdef</span> CONFIG_TRACE_IRQFLAGS</span></span><br><span class="line"> bl trace_hardirqs_on</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"> kernel_exit <span class="number">1</span></span><br><span class="line"><span class="built_in">ENDPROC</span>(el1_irq)</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> CONFIG_PREEMPT</span></span><br><span class="line">el1_preempt:</span><br><span class="line"> mov x24, lr</span><br><span class="line"> <span class="comment">// (3) 抢占调度</span></span><br><span class="line"><span class="number">1</span>: bl preempt_schedule_irq <span class="comment">// irq en/disable is done inside</span></span><br><span class="line"> ldr x0, [tsk, #TI_FLAGS] <span class="comment">// get new tasks TI_FLAGS</span></span><br><span class="line"> tbnz x0, #TIF_NEED_RESCHED, <span class="number">1</span>b <span class="comment">// needs rescheduling?</span></span><br><span class="line"> ret x24</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><br><span class="line"><span class="function">asmlinkage __visible <span class="type">void</span> __sched <span class="title">preempt_schedule_irq</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">enum</span> <span class="title class_">ctx_state</span> prev_state;</span><br><span class="line"></span><br><span class="line"> <span class="comment">/* Catch callers which need to be fixed */</span></span><br><span class="line"> <span class="built_in">BUG_ON</span>(<span class="built_in">preempt_count</span>() || !<span class="built_in">irqs_disabled</span>());</span><br><span class="line"></span><br><span class="line"> prev_state = <span class="built_in">exception_enter</span>();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">do</span> {</span><br><span class="line"> __preempt_count_add(PREEMPT_ACTIVE);</span><br><span class="line"> <span class="built_in">local_irq_enable</span>();</span><br><span class="line"> __schedule();</span><br><span class="line"> <span class="built_in">local_irq_disable</span>();</span><br><span class="line"> __preempt_count_sub(PREEMPT_ACTIVE);</span><br><span class="line"></span><br><span class="line"> <span class="comment">/*</span></span><br><span class="line"><span class="comment"> * Check again in case we missed a preemption opportunity</span></span><br><span class="line"><span class="comment"> * between schedule and now.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> <span class="built_in">barrier</span>();</span><br><span class="line"> } <span class="keyword">while</span> (<span class="built_in">need_resched</span>());</span><br><span class="line"></span><br><span class="line"> <span class="built_in">exception_exit</span>(prev_state);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>虽然 preempt_count>0 就是禁止抢占，Linux 进一步按照各种场景对 preempt_count bit 进行了资源划分：</p>
<table>
<thead>
<tr>
<th>reserved bits</th>
<th align="center">bit21</th>
<th align="center">bit20</th>
<th align="center">bit19-bit16</th>
<th align="center">bit15-bit8</th>
<th align="center">bit7-bit0</th>
</tr>
</thead>
<tbody><tr>
<td></td>
<td align="center">PREEMPT_ACTIVE</td>
<td align="center">NMI</td>
<td align="center">HARDIRQ</td>
<td align="center">SOFTIRQ</td>
<td align="center">PREEMPT</td>
</tr>
</tbody></table>
<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></pre></td><td class="code"><pre><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment"> * PREEMPT_MASK: 0x000000ff</span></span><br><span class="line"><span class="comment"> * SOFTIRQ_MASK: 0x0000ff00</span></span><br><span class="line"><span class="comment"> * HARDIRQ_MASK: 0x000f0000</span></span><br><span class="line"><span class="comment"> * NMI_MASK: 0x00100000</span></span><br><span class="line"><span class="comment"> * PREEMPT_ACTIVE: 0x00200000</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> PREEMPT_BITS 8</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> SOFTIRQ_BITS 8</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> HARDIRQ_BITS 4</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> NMI_BITS 1</span></span><br></pre></td></tr></table></figure>
<p>各场景分别利用各自的 bit 来 disable/enable 抢占：</p>
<ul>
<li>普通场景 (PREEMPT_MASK)。对应函数 <code>preempt_disable()</code>、<code>preempt_enable()</code>。</li>
<li>软中断场景 (SOFTIRQ_MASK)。对应函数 <code>local_bh_disable()</code>、<code>local_bh_enable()</code>。</li>
<li>普通中断场景 (HARDIRQ_MASK)。对应函数 <code>__irq_enter()</code>、<code>__irq_exit()</code>。</li>
<li>NMI 中断场景 (NMI_MASK)。对应函数 <code>nmi_enter()</code>、<code>nmi_exit()</code>。</li>
</ul>
<p>所以反过来，我们也可以通过 preempt_count 的值来判断当前在什么场景：</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></pre></td><td class="code"><pre><span class="line">#define in_irq() (<span class="name">hardirq_count</span>())</span><br><span class="line">#define in_softirq() (<span class="name">softirq_count</span>())</span><br><span class="line">#define in_interrupt() (<span class="name">irq_count</span>())</span><br><span class="line">#define in_serving_softirq() (<span class="name">softirq_count</span>() & SOFTIRQ_OFFSET)</span><br><span class="line">#define in_nmi() (<span class="name">preempt_count</span>() & NMI_MASK)</span><br><span class="line"></span><br><span class="line">#define hardirq_count() (<span class="name">preempt_count</span>() & HARDIRQ_MASK)</span><br><span class="line">#define softirq_count() (<span class="name">preempt_count</span>() & SOFTIRQ_MASK)</span><br><span class="line">#define irq_count() (<span class="name">preempt_count</span>() & (<span class="name">HARDIRQ_MASK</span> | SOFTIRQ_MASK \</span><br><span class="line"> | NMI_MASK))</span><br></pre></td></tr></table></figure>
<h3 id="2-2-softirq"><a href="#2-2-softirq" class="headerlink" title="2.2 softirq"></a>2.2 softirq</h3><p>回到中断上下半部的架构，linux 系统虽然将大部分工作移出了中断上下文，不关闭中断。但是它也希望移出的工作能够很快的得到执行，软中断为了保证自己能很快执行，使用 <code>__local_bh_disable_ip()</code> 禁止抢占。</p>
<p>softirq 的具体实现机制如下：</p>
<ul>
<li>系统支持固定的几种软中断，softirq_vec 数组用来记录这些软中断执行函数：</li>
</ul>
<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><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></pre></td><td class="code"><pre><span class="line">enum</span><br><span class="line">{</span><br><span class="line"> HI_SOFTIRQ=<span class="number">0</span>,</span><br><span class="line"> TIMER_SOFTIRQ,</span><br><span class="line"> NET_TX_SOFTIRQ,</span><br><span class="line"> NET_RX_SOFTIRQ,</span><br><span class="line"> BLOCK_SOFTIRQ,</span><br><span class="line"> BLOCK_IOPOLL_SOFTIRQ,</span><br><span class="line"> TASKLET_SOFTIRQ,</span><br><span class="line"> SCHED_SOFTIRQ,</span><br><span class="line"> HRTIMER_SOFTIRQ,</span><br><span class="line"> RCU_SOFTIRQ, <span class="regexp">/* Preferable RCU should always be the last softirq */</span></span><br><span class="line"></span><br><span class="line"> NR_SOFTIRQS</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="regexp">//</span> 注册软中断的服务程序</span><br><span class="line">void open_softir<span class="string">q(int nr, void (*action)</span>(struct softirq_action *))</span><br><span class="line">{</span><br><span class="line"> softirq_vec[nr].action = action;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">//TASKLET_SOFTIRQ、HI_SOFTIRQ 两个软中断用来给 tasklet 服务。</span><br><span class="line"> open_softir<span class="string">q(TASKLET_SOFTIRQ, tasklet_action)</span>;</span><br><span class="line"> open_softir<span class="string">q(HI_SOFTIRQ, tasklet_hi_action)</span>;</span><br></pre></td></tr></table></figure>
<ul>
<li>使用 irq_stat[cpu].__softirq_pending 来记录每个 cpu 上所有 softirq 的 pending 状态，<code>raise_softirq()</code> 用来置位一个 softirq pending：</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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">raise_softirq</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> nr)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">local_irq_save</span>(flags);</span><br><span class="line"> <span class="built_in">raise_softirq_irqoff</span>(nr);</span><br><span class="line"> <span class="built_in">local_irq_restore</span>(flags);</span><br><span class="line">}</span><br><span class="line">| →</span><br><span class="line"><span class="function"><span class="keyword">inline</span> <span class="type">void</span> <span class="title">raise_softirq_irqoff</span><span class="params">(<span class="type">unsigned</span> <span class="type">int</span> nr)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> __raise_softirq_irqoff(nr);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">in_interrupt</span>())</span><br><span class="line"> <span class="built_in">wakeup_softirqd</span>();</span><br><span class="line">}</span><br><span class="line">|| →</span><br><span class="line"><span class="type">void</span> __raise_softirq_irqoff(<span class="type">unsigned</span> <span class="type">int</span> nr)</span><br><span class="line">{</span><br><span class="line"> <span class="built_in">trace_softirq_raise</span>(nr);</span><br><span class="line"> <span class="built_in">or_softirq_pending</span>(<span class="number">1UL</span> << nr);</span><br><span class="line">}</span><br><span class="line">||| →</span><br><span class="line"><span class="meta">#<span class="keyword">define</span> or_softirq_pending(x) (local_softirq_pending() |= (x))</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">ifndef</span> __ARCH_IRQ_STAT</span></span><br><span class="line"><span class="keyword">extern</span> <span class="type">irq_cpustat_t</span> irq_stat[]; <span class="comment">/* defined in asm/hardirq.h */</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> __IRQ_STAT(cpu, member) (irq_stat[cpu].member)</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 class="comment">/* arch independent irq_stat fields */</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> local_softirq_pending() \</span></span><br><span class="line"><span class="meta"> __IRQ_STAT(smp_processor_id(), __softirq_pending)</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>
<ul>
<li>softirq 的执行有两个时刻：在退出中断 <code>irq_exit()</code> 时或者在 softirqd 线程当中：</li>
</ul>
<p><img src="int_softirq_flow.png" alt="linux 软中断流程 "></p>
<p>软中断使用 <code>smpboot_register_percpu_thread()</code> 函数，给每个 cpu 上创建了对应的 softirqd 线程：</p>
<figure class="highlight apache"><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></pre></td><td class="code"><pre><span class="line"><span class="attribute">root</span>@:/ # ps | grep softirq</span><br><span class="line"><span class="attribute">root</span> <span class="number">3</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> smpboot_th <span class="number">0000000000</span> S ksoftirqd/<span class="number">0</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">12</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">1</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">16</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">2</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">20</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">3</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">24</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">4</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">28</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">5</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">32</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">6</span></span><br><span class="line"><span class="attribute">root</span> <span class="number">36</span> <span class="number">2</span> <span class="number">0</span> <span class="number">0</span> __kthread_ <span class="number">0000000000</span> R ksoftirqd/<span class="number">7</span></span><br></pre></td></tr></table></figure>
<p>软中断优先在 <code>irq_exit()</code> 中执行，如果超过时间等条件转为 softirqd 线程中执行。满足以下任一条件软中断在 softirqd 线程中执行：</p>
<ul>
<li>在 <code>irq_exit()</code>-><code>__do_softirq()</code> 中运行，时间超过 2ms。</li>
<li>在 <code>irq_exit()</code>-><code>__do_softirq()</code> 中运行，轮询软中断超过 10 次。</li>
<li>在 <code>irq_exit()</code>-><code>__do_softirq()</code> 中运行，本线程需要被调度。</li>
<li>调用 <code>raise_softirq()</code> 唤醒软中断时，不在中断环境中。</li>
</ul>
<p>我们也看到，软中断处理是按照优先级逐个调用 softirq_vec[] 数组中的软中断处理函数，所以前面的软中断是可以阻塞后面的软中断的。这个在我们写程序的时候需要注意。</p>
<h3 id="2-3-tasklet"><a href="#2-3-tasklet" class="headerlink" title="2.3 tasklet"></a>2.3 tasklet</h3><p>Linux 已经有了 softirq 机制，为什么还需要 tasklet 机制？最主要的原因是 softirq 是多 cpu 执行的，可能碰到很多重入的问题，而 tasklet 同一时刻只能在一个 cpu 上执行，不需要处理重入互斥问题。另外 Linux 也不建议用户去添加新的软中断。</p>
<p>下面我们来具体分析一下 tasklet 的实现机制：</p>
<ul>
<li>per-cpu 变量 tasklet_vec/tasklet_hi_vec 以链表的形式记录了当前 cpu 需要处理的 tasklet 任务：</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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> __init <span class="title">softirq_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="type">int</span> cpu;</span><br><span class="line"></span><br><span class="line"> for_each_possible_cpu(cpu) {</span><br><span class="line"> <span class="comment">// (1)tasklet_vec 为低优先级的 tasklet 链表</span></span><br><span class="line"> <span class="built_in">per_cpu</span>(tasklet_vec, cpu).tail =</span><br><span class="line"> &<span class="built_in">per_cpu</span>(tasklet_vec, cpu).head;</span><br><span class="line"> <span class="comment">// (2)tasklet_hi_vec 为高优先级的 tasklet 链表</span></span><br><span class="line"> <span class="built_in">per_cpu</span>(tasklet_hi_vec, cpu).tail =</span><br><span class="line"> &<span class="built_in">per_cpu</span>(tasklet_hi_vec, cpu).head;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li>push 一个 tasklet 任务：</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></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">tasklet_schedule</span><span class="params">(<span class="keyword">struct</span> tasklet_struct *t)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">test_and_set_bit</span>(TASKLET_STATE_SCHED, &t->state))</span><br><span class="line"> __tasklet_schedule(t);</span><br><span class="line">}</span><br><span class="line">| →</span><br><span class="line"><span class="type">void</span> __tasklet_schedule(<span class="keyword">struct</span> tasklet_struct *t)</span><br><span class="line">{</span><br><span class="line"> <span class="type">unsigned</span> <span class="type">long</span> flags;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">local_irq_save</span>(flags);</span><br><span class="line"> <span class="comment">// (1) 将新的 tasklet 插入到本 cpu 链表尾部</span></span><br><span class="line"> t->next = <span class="literal">NULL</span>;</span><br><span class="line"> *__this_cpu_read(tasklet_vec.tail) = t;</span><br><span class="line"> __this_cpu_write(tasklet_vec.tail, &(t->next));</span><br><span class="line"> <span class="comment">// (2)raise 软中断来处理 tasklet</span></span><br><span class="line"> <span class="built_in">raise_softirq_irqoff</span>(TASKLET_SOFTIRQ);</span><br><span class="line"> <span class="built_in">local_irq_restore</span>(flags);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<ul>
<li>处理一个 tasklet 任务：</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></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">static</span> <span class="type">void</span> <span class="title">tasklet_action</span><span class="params">(<span class="keyword">struct</span> softirq_action *a)</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_">tasklet_struct</span> *list;</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="comment">// (1)list 取出当前链表中所有已有的 tasklet</span></span><br><span class="line"> list = __this_cpu_read(tasklet_vec.head);</span><br><span class="line"> <span class="comment">// (2)tasklet_vec.head 和 tasklet_vec.tail 返回初始化状态，继续接收新的 tasklet</span></span><br><span class="line"> __this_cpu_write(tasklet_vec.head, <span class="literal">NULL</span>);</span><br><span class="line"> __this_cpu_write(tasklet_vec.tail, <span class="built_in">this_cpu_ptr</span>(&tasklet_vec.head));</span><br><span class="line"> <span class="built_in">local_irq_enable</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (3) 逐个处理取出的 list 链表中的 tasklet</span></span><br><span class="line"> <span class="keyword">while</span> (list) {</span><br><span class="line"> <span class="keyword">struct</span> <span class="title class_">tasklet_struct</span> *t = list;</span><br><span class="line"></span><br><span class="line"> list = list->next;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (4)tasklet 互斥锁，保证 tasklet 同时只能在一个 cpu 上执行</span></span><br><span class="line"> <span class="keyword">if</span> (<span class="built_in">tasklet_trylock</span>(t)) {</span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">atomic_read</span>(&t->count)) {</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (6) 在 tasklet 运行前清除 TASKLET_STATE_SCHED 标志</span></span><br><span class="line"> <span class="comment">// 这个时候 tasklet 可以重新加入新的队列了，但是还不能执行</span></span><br><span class="line"> <span class="keyword">if</span> (!<span class="built_in">test_and_clear_bit</span>(TASKLET_STATE_SCHED,</span><br><span class="line"> &t->state))</span><br><span class="line"> <span class="built_in">BUG</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (7) 执行实际的 tasklet 处理函数</span></span><br><span class="line"> t-><span class="built_in">func</span>(t->data);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// (8) 释放 tasklet 锁，其他 cpu 可以运行这个 tasklet 了</span></span><br><span class="line"> <span class="built_in">tasklet_unlock</span>(t);</span><br><span class="line"> <span class="keyword">continue</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="built_in">tasklet_unlock</span>(t);</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="comment">// (5) 如果获取 tasklet 互斥锁失败，先加入到 cpu tasklet_vec 链表中</span></span><br><span class="line"> <span class="comment">// 下次执行</span></span><br><span class="line"> t->next = <span class="literal">NULL</span>;</span><br><span class="line"> *__this_cpu_read(tasklet_vec.tail) = t;</span><br><span class="line"> __this_cpu_write(tasklet_vec.tail, &(t->next));</span><br><span class="line"> __raise_softirq_irqoff(TASKLET_SOFTIRQ);</span><br><span class="line"> <span class="built_in">local_irq_enable</span>();</span><br><span class="line"> }</span><br><span class="line">}</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>[^ARMPG]: <a href="http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0024a/index.html">ARM Cortex-A Series Programmer’s Guide for ARMv8-A</a><br>[^GICANALY]: <a href="http://www.wowotech.net/irq_subsystem/gic_driver.html">GIC 代码分析 </a></p>
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