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@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linaro-kernel@lists.linaro.org
Link: http://lkml.kernel.org/r/000903ab3df3350943d3271c53615893a230dc95.1495603536.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 27d425e..30fd196 100644 (file)
--- 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 {