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SubjectRe: [patch 01/15] sched: (fixlet) dont update shares twice on on_rq parent
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On Tue, 2011-05-10 at 16:14 +0900, Hidetoshi Seto wrote:
> (2011/05/03 18:28), Paul Turner wrote:
> > In dequeue_task_fair() we bail on dequeue when we encounter a parenting entity
> > with additional weight. However, we perform a double shares update on this
> > entity since we continue the shares update traversal from that point, despite
> > dequeue_entity() having already updated its queuing cfs_rq.
> >
> > Avoid this by starting from the parent when we resume.
> >
> > Signed-off-by: Paul Turner <pjt@google.com>
> > ---
> > kernel/sched_fair.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > Index: tip/kernel/sched_fair.c
> > ===================================================================
> > --- tip.orig/kernel/sched_fair.c
> > +++ tip/kernel/sched_fair.c
> > @@ -1355,8 +1355,10 @@ static void dequeue_task_fair(struct rq
> > dequeue_entity(cfs_rq, se, flags);
> >
> > /* Don't dequeue parent if it has other entities besides us */
> > - if (cfs_rq->load.weight)
> > + if (cfs_rq->load.weight) {
> > + se = parent_entity(se);
> > break;
> > + }
> > flags |= DEQUEUE_SLEEP;
> > }
> >
>
> Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
>
> This small fixlet can stand alone.
> Peter, how about getting this into git tree first?

tip 2f36825b176f67e5c5228aa33d828bc39718811f contains the below.

/* Don't dequeue parent if it has other entities besides us */
- if (cfs_rq->load.weight)
+ if (cfs_rq->load.weight) {
+ /*
+ * Bias pick_next to pick a task from this cfs_rq, as
+ * p is sleeping when it is within its sched_slice.
+ */
+ if (task_sleep && parent_entity(se))
+ set_next_buddy(parent_entity(se));
break;
+ }
flags |= DEQUEUE_SLEEP;
}



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