sched: fix high wake up latencies with FAIR_USER_SCHED

patch 296825cbe14d4c95ee9c41ca5824f7487bfb4d9d in mainline.

The reason why we are getting better wakeup latencies for
!FAIR_USER_SCHED is because of this snippet of code in place_entity():

	if (!initial) {
		/* sleeps upto a single latency don't count. */
		if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se))
						     ^^^^^^^^^^^^^^^^^^
			vruntime -= sysctl_sched_latency;

		/* ensure we never gain time by being placed backwards. */
		vruntime = max_vruntime(se->vruntime, vruntime);
	}

NEW_FAIR_SLEEPERS feature gives credit for sleeping only to tasks and
not group-level entities. With the patch attached, I could see that
wakeup latencies with FAIR_USER_SCHED are restored to the same level as
!FAIR_USER_SCHED.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 94e88beb15f30f3bfafd69aaf9e6439a09a7746f..2288ad8496bfa8b05194d20feb4378c62fe455bf 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -511,7 +511,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 
        if (!initial) {
                /* sleeps upto a single latency don't count. */
-               if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se))
+               if (sched_feat(NEW_FAIR_SLEEPERS))
                        vruntime -= sysctl_sched_latency;
 
                /* ensure we never gain time by being placed backwards. */