linux-kernel - [PATCH 4/6] sched: fair: Avoid checking cfs_rq->nr

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Message-Id: <000903ab3df3350943d3271c53615893a230dc95.1495603536.git.viresh.kumar@linaro.org>
Date:   Wed, 24 May 2017 10:59:55 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 4/6] 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@...aro.org>
---
 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 fe03efd3880a..e519f6c03fe9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6267,10 +6267,10 @@ 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;
 
@@ -6300,11 +6300,17 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 			/*
 			 * 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);
@@ -6344,12 +6350,8 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
 
 	return p;
 simple:
-	cfs_rq = &rq->cfs;
 #endif
 
-	if (!cfs_rq->nr_running)
-		goto idle;
-
 	put_prev_task(rq, prev);
 
 	do {
-- 
2.13.0.70.g6367777092d9