[tip:sched/core] sched/fair: Avoid checking cfs_rq->nr_running twice

[tip-bot for Viresh Kumar]

Commit-ID:  9674f5cad22a590c865a330ce333026b9f9c078b
Gitweb:     http://git.kernel.org/tip/9674f5cad22a590c865a330ce333026b9f9c078b
Author:     Viresh Kumar <viresh.kumar@xxxxxxxxxx>
AuthorDate: Wed, 24 May 2017 10:59:55 +0530
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 10 Aug 2017 12:18:11 +0200

sched/fair: Avoid checking cfs_rq->nr_running twice

Rearrange pick_next_task_fair() a bit to avoid checking
cfs_rq->nr_running twice for the case where FAIR_GROUP_SCHED is enabled
and the previous task doesn't belong to the fair class.

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: linaro-kernel@xxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/000903ab3df3350943d3271c53615893a230dc95.1495603536.git.viresh.kumar@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/fair.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 27d425e..30fd196 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6187,10 +6187,10 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 	int new_tasks;
 
 again:
-#ifdef CONFIG_FAIR_GROUP_SCHED
 	if (!cfs_rq->nr_running)
 		goto idle;
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
 	if (prev->sched_class != &fair_sched_class)
 		goto simple;
 
@@ -6220,11 +6220,17 @@ again:
 			/*
 			 * This call to check_cfs_rq_runtime() will do the
 			 * throttle and dequeue its entity in the parent(s).
-			 * Therefore the 'simple' nr_running test will indeed
+			 * Therefore the nr_running test will indeed
 			 * be correct.
 			 */
-			if (unlikely(check_cfs_rq_runtime(cfs_rq)))
+			if (unlikely(check_cfs_rq_runtime(cfs_rq))) {
+				cfs_rq = &rq->cfs;
+
+				if (!cfs_rq->nr_running)
+					goto idle;
+
 				goto simple;
+			}
 		}
 
 		se = pick_next_entity(cfs_rq, curr);
@@ -6264,12 +6270,8 @@ again:
 
 	return p;
 simple:
-	cfs_rq = &rq->cfs;
 #endif
 
-	if (!cfs_rq->nr_running)
-		goto idle;
-
 	put_prev_task(rq, prev);
 
 	do {