android-mainline/ANDROID-sched-rt-Add-support-for-rt-sync-wakeups.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: "J. Avila" <elavila@google.com>
Date: Tue, 14 Jul 2020 22:03:38 +0000
Subject: ANDROID: sched/rt: Add support for rt sync wakeups

Some rt tasks undergo sync wakeup. Currently, these tasks will be placed
on other, often sleeping or otherwise idle CPUs, which can lead to
unnecessary power hits. Support rt sync wakeups, but only enable
rt sync for SMP targets.

Bug: 157906395
Change-Id: I48864d0847bbe4f7813c842032880ad3f3b8b06b
Signed-off-by: J. Avila <elavila@google.com>
[quic_dickey@quicinc.com: Port to mainline]
Signed-off-by: Stephen Dickey <quic_dickey@quicinc.com>
Signed-off-by: Lee Jones <joneslee@google.com>
---
 kernel/sched/core.c  |  3 +++
 kernel/sched/rt.c    | 39 ++++++++++++++++++++++++++++++++++++++-
 kernel/sched/sched.h |  2 ++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3669,6 +3669,9 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
 {
 	int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;
 
+	if (wake_flags & WF_SYNC)
+		en_flags |= ENQUEUE_WAKEUP_SYNC;
+
 	lockdep_assert_rq_held(rq);
 
 	if (p->sched_contributes_to_load)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1528,6 +1528,27 @@ static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
 	enqueue_top_rt_rq(&rq->rt);
 }
 
+#ifdef CONFIG_SMP
+static inline bool should_honor_rt_sync(struct rq *rq, struct task_struct *p,
+					bool sync)
+{
+	/*
+	 * If the waker is CFS, then an RT sync wakeup would preempt the waker
+	 * and force it to run for a likely small time after the RT wakee is
+	 * done. So, only honor RT sync wakeups from RT wakers.
+	 */
+	return sync && task_has_rt_policy(rq->curr) &&
+		p->prio <= rq->rt.highest_prio.next &&
+		rq->rt.rt_nr_running <= 2;
+}
+#else
+static inline bool should_honor_rt_sync(struct rq *rq, struct task_struct *p,
+					bool sync)
+{
+	return 0;
+}
+#endif
+
 /*
  * Adding/removing a task to/from a priority array:
  */
@@ -1535,6 +1556,7 @@ static void
 enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
 {
 	struct sched_rt_entity *rt_se = &p->rt;
+	bool sync = !!(flags & ENQUEUE_WAKEUP_SYNC);
 
 	if (flags & ENQUEUE_WAKEUP)
 		rt_se->timeout = 0;
@@ -1544,7 +1566,8 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
 
 	enqueue_rt_entity(rt_se, flags);
 
-	if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
+	if (!task_current(rq, p) && p->nr_cpus_allowed > 1 &&
+	    !should_honor_rt_sync(rq, p, sync))
 		enqueue_pushable_task(rq, p);
 }
 
@@ -1600,7 +1623,10 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 {
 	struct task_struct *curr;
 	struct rq *rq;
+	struct rq *this_cpu_rq;
 	bool test;
+	bool sync = !!(flags & WF_SYNC);
+	int this_cpu;
 
 	/* For anything but wake ups, just return the task_cpu */
 	if (!(flags & (WF_TTWU | WF_FORK)))
@@ -1610,6 +1636,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 
 	rcu_read_lock();
 	curr = READ_ONCE(rq->curr); /* unlocked access */
+	this_cpu = smp_processor_id();
+	this_cpu_rq = cpu_rq(this_cpu);
 
 	/*
 	 * If the current task on @p's runqueue is an RT task, then
@@ -1641,6 +1669,15 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
 	       unlikely(rt_task(curr)) &&
 	       (curr->nr_cpus_allowed < 2 || curr->prio <= p->prio);
 
+	/*
+	 * Respect the sync flag as long as the task can run on this CPU.
+	 */
+	if (should_honor_rt_sync(this_cpu_rq, p, sync) &&
+	    cpumask_test_cpu(this_cpu, p->cpus_ptr)) {
+		cpu = this_cpu;
+		goto out_unlock;
+	}
+
 	if (test || !rt_task_fits_capacity(p, cpu)) {
 		int target = find_lowest_rq(p);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2155,6 +2155,8 @@ extern const u32		sched_prio_to_wmult[40];
 #define ENQUEUE_MIGRATED	0x00
 #endif
 
+#define ENQUEUE_WAKEUP_SYNC	0x80
+
 #define RETRY_TASK		((void *)-1UL)
 
 struct affinity_context {