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Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork

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On Tue, Nov 29, 2016 at 02:04:27PM +0100, Vincent Guittot wrote:
> On 29 November 2016 at 11:57, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
> > On Fri, Nov 25, 2016 at 04:34:32PM +0100, Vincent Guittot wrote:
> >> @@ -5708,13 +5708,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> >>
> >>       avg_cost = this_sd->avg_scan_cost;
> >>
> >> -     /*
> >> -      * Due to large variance we need a large fuzz factor; hackbench in
> >> -      * particularly is sensitive here.
> >> -      */
> >> -     if ((avg_idle / 512) < avg_cost)
> >> -             return -1;
> >> -
> >>       time = local_clock();
> >>
> >>       for_each_cpu_wrap(cpu, sched_domain_span(sd), target, wrap) {
> >
> > I don't quite get this fix, but it is very likely because I haven't paid
> > enough attention.
> >
> > Are you saying that removing the avg_cost check is improving hackbench
> > performance? I thought it was supposed to help hackbench? I'm confused
> > :-(
> 
> Yes, avg_cost check prevents some tasks migration at the end of the
> tests when some threads have already finished their loop letting some
> CPUs idle whereas others threads are still competing on the same CPUS

Okay, thanks.

> > Should we do the same for SD_BALANCE_EXEC?
> 
> I asked myself if i should add SD_BALANCE_EXEC but decided to only
> keep SD_BALANCE_FORK for now as no regression has been raised for now.

Fair enough.

FWIW, with the label renaming suggested by mfleming, you can add my
reviewed/acked-by if you like.

Morten

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[PATCH 0/2 v2] sched: improve spread of tasks during fork  Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-25 16:40 +0100
  [PATCH 1/2 v2] sched: fix find_idlest_group for fork Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-25 16:40 +0100
    Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Matt Fleming <matt@codeblueprint.co.uk> - 2016-11-28 18:10 +0100
      Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-28 18:30 +0100
    Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Morten Rasmussen <morten.rasmussen@arm.com> - 2016-11-29 12:00 +0100
      Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Peter Zijlstra <peterz@infradead.org> - 2016-11-29 12:50 +0100
        Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Matt Fleming <matt@codeblueprint.co.uk> - 2016-11-29 12:50 +0100
          Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Peter Zijlstra <peterz@infradead.org> - 2016-11-29 13:40 +0100
        Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Morten Rasmussen <morten.rasmussen@arm.com> - 2016-11-29 15:50 +0100
          Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Peter Zijlstra <peterz@infradead.org> - 2016-12-05 10:00 +0100
      Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-29 14:10 +0100
        Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-29 16:00 +0100
        Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Morten Rasmussen <morten.rasmussen@arm.com> - 2016-11-29 16:00 +0100
    Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Matt Fleming <matt@codeblueprint.co.uk> - 2016-12-04 00:30 +0100
      Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork Vincent Guittot <vincent.guittot@linaro.org> - 2016-12-05 10:40 +0100
  Re: [PATCH 0/2 v2] sched: improve spread of tasks during fork Matt Fleming <matt@codeblueprint.co.uk> - 2016-11-28 18:10 +0100
    Re: [PATCH 0/2 v2] sched: improve spread of tasks during fork Vincent Guittot <vincent.guittot@linaro.org> - 2016-11-28 18:30 +0100

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