sched: Move rq->idle_stamp up to the core

idle_balance() modifies the rq->idle_stamp field, making this information
shared across core.c and fair.c.

As we know if the cpu is going to idle or not with the previous patch, let's
encapsulate the rq->idle_stamp information in core.c by moving it up to the
caller.

The idle_balance() function returns true in case a balancing occured and the
cpu won't be idle, false if no balance happened and the cpu is going idle.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: alex.shi@linaro.org
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389949444-14821-3-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 74dd565c2e1b..417cf657a606 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2704,8 +2704,15 @@ need_resched:
 
 	pre_schedule(rq, prev);
 
-	if (unlikely(!rq->nr_running))
-		idle_balance(rq);
+	if (unlikely(!rq->nr_running)) {
+		/*
+		 * We must set idle_stamp _before_ calling idle_balance(), such
+		 * that we measure the duration of idle_balance() as idle time.
+		 */
+		rq->idle_stamp = rq_clock(rq);
+		if (idle_balance(rq))
+			rq->idle_stamp = 0;
+	}
 
 	put_prev_task(rq, prev);
 	next = pick_next_task(rq);