linux-kernel - [PATCH 3.14 046/130] sched, rt: Convert switched_{from, to}_rt() / prio_changed

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Date:	Tue, 01 Mar 2016 23:51:05 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	<ktkhai@...allels.com>, <rostedt@...dmis.org>,
	<juri.lelli@...il.com>, <pang.xunlei@...aro.org>,
	<oleg@...hat.com>, <wanpeng.li@...ux.intel.com>,
	<umgwanakikbuti@...il.com>, Thomas Gleixner <tglx@...utronix.de>,
	Byungchul Park <byungchul.park@....com>
Subject: [PATCH 3.14 046/130] sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@...radead.org>

commit fd7a4bed183523275279c9addbf42fce550c2e90 upstream.

Remove the direct {push,pull} balancing operations from
switched_{from,to}_rt() / prio_changed_rt() and use the balance
callback queue.

Again, err on the side of too many reschedules; since too few is a
hard bug while too many is just annoying.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: ktkhai@...allels.com
Cc: rostedt@...dmis.org
Cc: juri.lelli@...il.com
Cc: pang.xunlei@...aro.org
Cc: oleg@...hat.com
Cc: wanpeng.li@...ux.intel.com
Cc: umgwanakikbuti@...il.com
Link: http://lkml.kernel.org/r/20150611124742.766832367@infradead.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Byungchul Park <byungchul.park@....com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/sched/rt.c |   35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -315,16 +315,23 @@ static inline int has_pushable_tasks(str
 	return !plist_head_empty(&rq->rt.pushable_tasks);
 }
 
-static DEFINE_PER_CPU(struct callback_head, rt_balance_head);
+static DEFINE_PER_CPU(struct callback_head, rt_push_head);
+static DEFINE_PER_CPU(struct callback_head, rt_pull_head);
 
 static void push_rt_tasks(struct rq *);
+static void pull_rt_task(struct rq *);
 
 static inline void queue_push_tasks(struct rq *rq)
 {
 	if (!has_pushable_tasks(rq))
 		return;
 
-	queue_balance_callback(rq, &per_cpu(rt_balance_head, rq->cpu), push_rt_tasks);
+	queue_balance_callback(rq, &per_cpu(rt_push_head, rq->cpu), push_rt_tasks);
+}
+
+static inline void queue_pull_task(struct rq *rq)
+{
+	queue_balance_callback(rq, &per_cpu(rt_pull_head, rq->cpu), pull_rt_task);
 }
 
 static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
@@ -1837,7 +1844,7 @@ static void switched_from_rt(struct rq *
 	if (!p->on_rq || rq->rt.rt_nr_running)
 		return;
 
-	pull_rt_task(rq);
+	queue_pull_task(rq);
 }
 
 void init_sched_rt_class(void)
@@ -1858,8 +1865,6 @@ void init_sched_rt_class(void)
  */
 static void switched_to_rt(struct rq *rq, struct task_struct *p)
 {
-	int check_resched = 1;
-
 	/*
 	 * If we are already running, then there's nothing
 	 * that needs to be done. But if we are not running
@@ -1869,13 +1874,12 @@ static void switched_to_rt(struct rq *rq
 	 */
 	if (p->on_rq && rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->rt.overloaded && push_rt_task(rq) &&
-		    /* Don't resched if we changed runqueues */
-		    rq != task_rq(p))
-			check_resched = 0;
-#endif /* CONFIG_SMP */
-		if (check_resched && p->prio < rq->curr->prio)
+		if (rq->rt.overloaded)
+			queue_push_tasks(rq);
+#else
+		if (p->prio < rq->curr->prio)
 			resched_task(rq->curr);
+#endif /* CONFIG_SMP */
 	}
 }
 
@@ -1896,14 +1900,13 @@ prio_changed_rt(struct rq *rq, struct ta
 		 * may need to pull tasks to this runqueue.
 		 */
 		if (oldprio < p->prio)
-			pull_rt_task(rq);
+			queue_pull_task(rq);
+
 		/*
 		 * If there's a higher priority task waiting to run
-		 * then reschedule. Note, the above pull_rt_task
-		 * can release the rq lock and p could migrate.
-		 * Only reschedule if p is still on the same runqueue.
+		 * then reschedule.
 		 */
-		if (p->prio > rq->rt.highest_prio.curr && rq->curr == p)
+		if (p->prio > rq->rt.highest_prio.curr)
 			resched_task(p);
 #else
 		/* For UP simply resched on drop of prio */