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[v4.8-rc1,Regression] sched/fair: Apply more PELT fixes

Message ID 20161017090903.GA11962@linaro.org
State New
Headers show

Commit Message

Vincent Guittot Oct. 17, 2016, 9:09 a.m. UTC 
Le Friday 14 Oct 2016 à 12:04:02 (-0400), Joseph Salisbury a écrit :
> On 10/14/2016 11:18 AM, Vincent Guittot wrote:

> > Le Friday 14 Oct 2016 à 14:10:07 (+0100), Dietmar Eggemann a écrit :

> >> On 14/10/16 09:24, Vincent Guittot wrote:

> >>> On 13 October 2016 at 23:34, Vincent Guittot <vincent.guittot@linaro.org> wrote:

> >>>> On 13 October 2016 at 20:49, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:

> >>>>> On 13/10/16 17:48, Vincent Guittot wrote:

> >>>>>> On 13 October 2016 at 17:52, Joseph Salisbury

> >>>>>> <joseph.salisbury@canonical.com> wrote:

> >>>>>>> On 10/13/2016 06:58 AM, Vincent Guittot wrote:

> >>>>>>>> Hi,

> >>>>>>>>

> >>>>>>>> On 12 October 2016 at 18:21, Joseph Salisbury

> >>>>>>>> <joseph.salisbury@canonical.com> wrote:

> >>>>>>>>> On 10/12/2016 08:20 AM, Vincent Guittot wrote:

> >>>>>>>>>> On 8 October 2016 at 13:49, Mike Galbraith <efault@gmx.de> wrote:

> >>>>>>>>>>> On Sat, 2016-10-08 at 13:37 +0200, Vincent Guittot wrote:

> >>>>>>>>>>>> On 8 October 2016 at 10:39, Ingo Molnar <mingo@kernel.org> wrote:

> >>>>>>>>>>>>> * Peter Zijlstra <peterz@infradead.org> wrote:

> >>>>>>>>>>>>>

> >>>>>>>>>>>>>> On Fri, Oct 07, 2016 at 03:38:23PM -0400, Joseph Salisbury wrote:

> >> [...]

> >>

> >>>>> When I create a tg_root/tg_x/tg_y_1 and a tg_root/tg_x/tg_y_2 group, the tg_x->load_avg

> >>>>> becomes > 6*1024 before any tasks ran in it.

> >>>> This is normal as se->avg.load_avg is initialized to

> >>>> scale_load_down(se->load.weight) and this se->avg.load_avg will be

> >>>> added to tg_x[cpu]->cfs_rq->avg.load_avg when attached to the cfs_rq

> >> Yeah, you right, even when I've created 50 second level groups,

> >> tg_x->load_avg is ~6800.

> >>

> >> Could it have something to do with the fact that .se->load.weight = 2

> >> for all these task groups? on a 64bit system?

> > I don't think so, the problem really comes from tg->load_avg = 381697

> > but sum of cfs_rq[cpu]->tg_load_avg_contrib = 1013 which is << tg->load_avg

> > and cfs_rq[cpu]->tg_load_avg_contrib == cfs_rq[cpu]->avg.load_avg so we can't 

> > expect any negative delta to remove this large value

> >

> >> In case we call  __update_load_avg(..., se->on_rq *

> >> scale_load_down(se->load.weight), ...) we pass a weight argument of 0

> >> for these se's.

> >>

> >> Does not happen with:

> >>

> >> -       if (shares < MIN_SHARES)

> >> -               shares = MIN_SHARES;

> >> +       if (shares < scale_load(MIN_SHARES))

> >> +               shares = scale_load(MIN_SHARES);

> >>

> >> in  calc_cfs_shares().

> >>

> >> [...]

> >>

> >>

> Adding Omer to CC list, as he is able to reproduce this bug.


Could you try the patch below on top of the faulty kernel ?

---
 kernel/sched/fair.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

-- 
2.7.4


>
diff mbox

Patch

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8b03fb5..8926685 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2902,7 +2902,8 @@  __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
  */
 static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
 {
-	long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;
+	unsigned long load_avg = READ_ONCE(cfs_rq->avg.load_avg);
+	long delta = load_avg - cfs_rq->tg_load_avg_contrib;
 
 	/*
 	 * No need to update load_avg for root_task_group as it is not used.
@@ -2912,7 +2913,7 @@  static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
 
 	if (force || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
 		atomic_long_add(delta, &cfs_rq->tg->load_avg);
-		cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg;
+		cfs_rq->tg_load_avg_contrib = load_avg;
 	}
 }