rtgang-v5.15.patch

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e418935f8..3126bd8a8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -803,6 +803,9 @@ struct task_struct {
 	struct uclamp_se		uclamp[UCLAMP_CNT];
 #endif
 
+	/* Throttling related fields */
+	int corun_threshold_events;
+
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 	/* List of struct preempt_notifier: */
 	struct hlist_head		preempt_notifiers;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 252243c77..97e8c72cc 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -988,6 +988,7 @@ asmlinkage long sys_process_vm_writev(pid_t pid,
 				      const struct iovec __user *rvec,
 				      unsigned long riovcnt,
 				      unsigned long flags);
+asmlinkage long sys_bwlock(pid_t pid, int cte);
 asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
 			 unsigned long idx1, unsigned long idx2);
 asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 1c5fb86d4..eb2ead400 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -702,6 +702,9 @@ __SC_COMP_3264(__NR_recvmmsg, sys_recvmmsg_time32, sys_recvmmsg, compat_sys_recv
  */
 #define __NR_arch_specific_syscall 244
 
+#define __NR_bwlock 255
+__SYSCALL(__NR_bwlock, sys_bwlock)
+
 #if defined(__ARCH_WANT_TIME32_SYSCALLS) || __BITS_PER_LONG != 32
 #define __NR_wait4 260
 __SC_COMP(__NR_wait4, sys_wait4, compat_sys_wait4)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c1458fa8b..ea1a5004f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -994,6 +994,31 @@ void resched_cpu(int cpu)
 	raw_spin_rq_unlock_irqrestore(rq, flags);
 }
 
+/*
+ * The purpose of this function is to force rescheduling of a target cpu under
+ * all circumstances. For this reason, this function does not acquire the
+ * target CPU's rq lock and sends a rescheduling interrupt without protection
+ * if need be. It is used exclusively in RT-Gang related code.
+ */
+void resched_cpu_force (int cpu)
+{
+	struct rq *rq = cpu_rq(cpu);
+	struct task_struct *curr = rq->curr;
+
+	cpu = cpu_of(rq);
+
+	if (cpu == smp_processor_id()) {
+		set_tsk_need_resched(curr);
+		set_preempt_need_resched();
+		return;
+	}
+
+	if (set_nr_and_not_polling(curr))
+		smp_send_reschedule(cpu);
+	else
+		trace_sched_wake_idle_without_ipi(cpu);
+}
+
 #ifdef CONFIG_SMP
 #ifdef CONFIG_NO_HZ_COMMON
 /*
@@ -5658,6 +5683,8 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 
 	for_each_class(class) {
 		p = class->pick_next_task(rq);
+		if (p == BLOCK_TASK)
+			continue;
 		if (p)
 			return p;
 	}
@@ -7757,6 +7784,34 @@ static void get_params(struct task_struct *p, struct sched_attr *attr)
 		attr->sched_nice = task_nice(p);
 }
 
+/*
+ * sys_bwlock - Memory bandwidth control lock. Provides exclusive access to
+ * main memory to the holder. Holder must be a real-time task
+ *
+ * @pid	: pid of the process which wants to hold bandwidth lock
+ * @cte : Safe memory usage threshold for corunning tasks
+ */
+SYSCALL_DEFINE2(bwlock, pid_t, pid, int, cte)
+{
+	struct task_struct *p;
+
+	/* Obtain the task structure associated with the process
+	   referenced by pid */
+	if (pid == 0 || current->pid == pid)
+		p = current;
+	else
+		p = find_process_by_pid (pid);
+
+	/* Process does not exist or it is not a real-time process */
+	if (!p || !rt_task (p))
+		return -1;
+
+	p->corun_threshold_events = cte;
+
+	/* Return with success */
+	return 0;
+}
+
 /**
  * sys_sched_setscheduler - set/change the scheduler policy and RT priority
  * @pid: the pid in question.
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index c4947c1b5..959b3194a 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -6,6 +6,14 @@
  */
 SCHED_FEAT(GENTLE_FAIR_SLEEPERS, true)
 
+/*
+ * Enable real-time gang scheduling framework (RT-Gang). RT-Gang allows
+ * execution of a single (multi-threaded) real-time task (i.e., gang) at any
+ * giving time across all system cores.
+ * NOTE: This feature is disabled by default.
+ */
+SCHED_FEAT(RT_GANG_LOCK, false)
+
 /*
  * Place new tasks ahead so that they do not starve already running
  * tasks
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index add67f811..7aab4186a 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -7,11 +7,103 @@
 
 #include "pelt.h"
 
+rt_gang_lock_t	rt_gang_lock;
+rt_gang_lock_t	*rt_glock = &rt_gang_lock;
+int be_mem_threshold = SYS_MAX_LLC_EVENTS;
+EXPORT_SYMBOL(be_mem_threshold);
+
 int sched_rr_timeslice = RR_TIMESLICE;
 int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;
 /* More than 4 hours if BW_SHIFT equals 20. */
 static const u64 max_rt_runtime = MAX_BW;
 
+static inline void gang_lock_cpu(struct task_struct *thread)
+{
+	int cpu = smp_processor_id();
+
+	TRACER(thread, "Adding new gang member");
+	cpumask_set_cpu(cpu, rt_glock->locked_cores);
+	rt_glock->gthreads [cpu] = thread;
+
+	return;
+}
+
+static inline void resched_cpus(cpumask_var_t mask)
+{
+	int cpu;
+	int this_cpu = smp_processor_id();
+
+	for_each_cpu (cpu, mask) {
+		if (cpu == this_cpu)
+			continue;
+
+		resched_cpu_force(cpu);
+	}
+	return;
+}
+
+static inline void do_gang_preemption(void)
+{
+	int cpu;
+	int this_cpu = smp_processor_id();
+
+	for_each_cpu (cpu, rt_glock->locked_cores) {
+		WARN_ON(rt_glock->gthreads[cpu] == NULL);
+		TRACER(rt_glock->gthreads[cpu], "Preempting thread");
+
+                set_tsk_need_resched(rt_glock->gthreads[cpu]);
+
+		rt_glock->gthreads[cpu] = NULL;
+		if (cpu != this_cpu)
+			resched_cpu_force(cpu);
+	}
+
+	cpumask_clear(rt_glock->locked_cores);
+
+	return;
+}
+
+static inline void try_glock_release(struct task_struct *thread)
+{
+	int cpu;
+
+	WARN_ON(cpumask_weight(rt_glock->locked_cores) == 0);
+
+	/*
+	 * Release RT-Gang lock of 'prev' task on all cores it may have ran on.
+	 * Migrated tasks can hold lock on multiple cores.
+	 */
+	for_each_cpu (cpu, rt_glock->locked_cores) {
+		if (rt_glock->gthreads [cpu] == thread) {
+			TRACER(thread, "Releasing lock");
+			WARN_ON(!rt_prio(thread->prio));
+			cpumask_clear_cpu(cpu, rt_glock->locked_cores);
+		}
+	}
+
+	if (cpumask_weight(rt_glock->locked_cores) == 0) {
+		/* RT-Gang lock is now free. Reschedule blocked cores. */
+		TRACER(thread, "Lock free");
+		rt_glock->prio = INT_MAX;
+		rt_glock->lock_held = false;
+		be_mem_threshold = SYS_MAX_LLC_EVENTS;
+		resched_cpus(rt_glock->blocked_cores);
+		cpumask_clear(rt_glock->blocked_cores);
+	}
+
+	return;
+}
+
+static inline void update_mem_threshold(struct task_struct *thread)
+{
+	if (thread->corun_threshold_events)
+		be_mem_threshold = thread->corun_threshold_events;
+	else
+		be_mem_threshold = SYS_DEFAULT_LLC_EVENTS;
+
+	return;
+}
+
 static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
 
 struct rt_bandwidth def_rt_bandwidth;
@@ -1661,8 +1753,54 @@ static struct task_struct *pick_next_task_rt(struct rq *rq)
 {
 	struct task_struct *p = pick_task_rt(rq);
 
-	if (p)
-		set_next_task_rt(rq, p, true);
+	/* If no tasks, it can be NULL */
+	if (!p)
+		return NULL;
+
+	/* Do not apply RT gang to high-priority kernel threads */
+	if (sched_feat(RT_GANG_LOCK) && p->mm &&
+	    (p->prio > RT_SYS_PRIO_THRESHOLD))
+	{
+		raw_spin_lock(&rt_glock->lock);
+		if (!rt_glock->lock_held) {
+			/* No RT gang exist currently; begin a new gang */
+			BUG_ON(cpumask_weight(rt_glock->locked_cores) != 0);
+			BUG_ON(cpumask_weight(rt_glock->blocked_cores) != 0);
+
+			TRACER(p, "Acquiring lock");
+			rt_glock->prio = p->prio;
+			gang_lock_cpu(p);
+			rt_glock->lock_held = true;
+			update_mem_threshold(p);
+		} else {
+			BUG_ON(cpumask_weight(rt_glock->locked_cores) == 0);
+			if (rt_glock->prio > p->prio) {
+				/* 'p' has higher priority; preempt */
+				TRACER(p, "Preempted by gang");
+				do_gang_preemption();
+				rt_glock->prio = p->prio;
+				gang_lock_cpu(p);
+				update_mem_threshold(p);
+			} else if (p->prio == rt_glock->prio) {
+				/* 'p' is part of the current RT gang */
+				gang_lock_cpu(p);
+			} else {
+				int this_cpu = smp_processor_id();
+				/* 'p' has lower priority; blocked */
+				if (!cpumask_test_cpu(this_cpu,
+					      rt_glock->blocked_cores)) {
+					TRACER(p, "Blocking gang");
+					cpumask_set_cpu(this_cpu,
+						rt_glock->blocked_cores);
+				}
+				raw_spin_unlock(&rt_glock->lock);
+				return BLOCK_TASK;
+			}
+		}
+		raw_spin_unlock(&rt_glock->lock);
+	}
+
+	set_next_task_rt(rq, p, true);
 
 	return p;
 }
@@ -1671,6 +1809,15 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
 {
 	update_curr_rt(rq);
 
+	/* If 'prev' is a member of the current RT gang, update the
+	 * locked_cores mask and release the RT gang lock if necessary. */
+	if (sched_feat(RT_GANG_LOCK))
+	{
+		raw_spin_lock(&rt_glock->lock);
+		if (rt_glock->lock_held)
+			try_glock_release(p);
+		raw_spin_unlock(&rt_glock->lock);
+	}
 	update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 1);
 
 	/*
@@ -2361,6 +2508,8 @@ void __init init_sched_rt_class(void)
 		zalloc_cpumask_var_node(&per_cpu(local_cpu_mask, i),
 					GFP_KERNEL, cpu_to_node(i));
 	}
+
+	INIT_GANG_LOCK();
 }
 #endif /* CONFIG_SMP */
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e1f46ed41..c3ab354f2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2117,6 +2117,7 @@ extern const u32		sched_prio_to_wmult[40];
 #endif
 
 #define RETRY_TASK		((void *)-1UL)
+#define BLOCK_TASK		((void *)-2UL)
 
 struct sched_class {
 
@@ -2325,6 +2326,7 @@ extern void reweight_task(struct task_struct *p, int prio);
 
 extern void resched_curr(struct rq *rq);
 extern void resched_cpu(int cpu);
+extern void resched_cpu_force(int cpu);
 
 extern struct rt_bandwidth def_rt_bandwidth;
 extern void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime);
@@ -3102,3 +3104,54 @@ extern int sched_dynamic_mode(const char *str);
 extern void sched_dynamic_update(int mode);
 #endif
 
+/*
+ * GANG SCHEDULING RELATED DECLARATIONS
+ */
+typedef struct rt_gang_lock {
+	raw_spinlock_t		lock;
+	bool			lock_held;
+	cpumask_var_t		locked_cores;
+	cpumask_var_t		blocked_cores;
+	int			prio;
+	struct task_struct*	gthreads [NR_CPUS];
+} rt_gang_lock_t;
+
+extern int be_mem_threshold;
+extern rt_gang_lock_t	*rt_glock;
+
+#define RT_SYS_PRIO_THRESHOLD		(50)
+#define INIT_GANG_LOCK()						\
+do {									\
+	int i = 0;							\
+	raw_spin_lock_init(&rt_glock->lock);				\
+	rt_glock->lock_held = false;					\
+	zalloc_cpumask_var(&rt_glock->locked_cores, GFP_KERNEL);	\
+	zalloc_cpumask_var(&rt_glock->blocked_cores, GFP_KERNEL);	\
+	rt_glock->prio = INT_MAX;					\
+	for (; i < NR_CPUS; i++)					\
+		rt_glock->gthreads [i] = NULL;				\
+} while (0);
+
+/*
+ * Default memory usage threshold for best-effort tasks. On a system with
+ * 64-Byte cache line size, this equals 100 GBytes/sec i.e., no throttling.
+ */
+#define	SYS_MAX_LLC_EVENTS		(1638400)
+
+/*
+ * The following budget (for using main memory) is applied by default to all
+ * best-effort tasks on a per-core basis while a real-time task is executing.
+ * On a system with 64-Byte cache line size, the value specified below comes
+ * out to be 100 MBytes/sec.
+ * The goal here is to throttle 'aggressively' by default so that the
+ * best-effort tasks are not able to interfere with the real-time tasks.
+ */
+#define	SYS_DEFAULT_LLC_EVENTS		(1638)
+
+#define RT_GANG_DEBUG
+#ifdef RT_GANG_DEBUG
+#define TRACER(task, msg)		trace_printk("[G:] %s\n", msg)
+#else
+#define TRACER(task, msg)
+#endif
+