[patch 41/45] sched: fix high wake up latencies with FAIR_USER_SCHED

Greg KH
2008-02-07T21:13:51Z

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2.6.24-stable review patch. If anyone has any objections, please let us know.

------------------
From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

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>

---
kernel/sched_fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -511,7 +511,7 @@ place_entity(struct cfs_rq *cfs_rq, stru

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. */

--