sched: Push put_prev_task() into pick_next_task()

In order to avoid having to do put/set on a whole cgroup hierarchy
when we context switch, push the put into pick_next_task() so that
both operations are in the same function. Further changes then allow
us to possibly optimize away redundant work.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1328936700.2476.17.camel@laptop
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 8 insertions, 13 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 417cf657a606..dedb5f07666e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2579,18 +2579,11 @@ static inline void schedule_debug(struct task_struct *prev)
 	schedstat_inc(this_rq(), sched_count);
 }
 
-static void put_prev_task(struct rq *rq, struct task_struct *prev)
-{
-	if (prev->on_rq || rq->skip_clock_update < 0)
-		update_rq_clock(rq);
-	prev->sched_class->put_prev_task(rq, prev);
-}
-
 /*
  * Pick up the highest-prio task:
  */
 static inline struct task_struct *
-pick_next_task(struct rq *rq)
+pick_next_task(struct rq *rq, struct task_struct *prev)
 {
 	const struct sched_class *class;
 	struct task_struct *p;
@@ -2600,13 +2593,13 @@ pick_next_task(struct rq *rq)
 	 * the fair class we can call that function directly:
 	 */
 	if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
-		p = fair_sched_class.pick_next_task(rq);
+		p = fair_sched_class.pick_next_task(rq, prev);
 		if (likely(p))
 			return p;
 	}
 
 	for_each_class(class) {
-		p = class->pick_next_task(rq);
+		p = class->pick_next_task(rq, prev);
 		if (p)
 			return p;
 	}
@@ -2714,8 +2707,10 @@ need_resched:
 			rq->idle_stamp = 0;
 	}
 
-	put_prev_task(rq, prev);
-	next = pick_next_task(rq);
+	if (prev->on_rq || rq->skip_clock_update < 0)
+		update_rq_clock(rq);
+
+	next = pick_next_task(rq, prev);
 	clear_tsk_need_resched(prev);
 	clear_preempt_need_resched();
 	rq->skip_clock_update = 0;
@@ -4748,7 +4743,7 @@ static void migrate_tasks(unsigned int dead_cpu)
 		if (rq->nr_running == 1)
 			break;
 
-		next = pick_next_task(rq);
+		next = pick_next_task(rq, NULL);
 		BUG_ON(!next);
 		next->sched_class->put_prev_task(rq, next);