linux-kernel - Re: [PATCH] sched/pelt: fix update_blocked

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Message-ID: <CAKfTPtBPmQBtq5xvpVP59X4OqQcodTpT2djqVWKeW8X-CkhwOA@mail.gmail.com>
Date:   Fri, 31 Aug 2018 16:45:13 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/pelt: fix update_blocked_averages() for dl and rt

On Fri, 31 Aug 2018 at 16:41, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Aug 31, 2018 at 03:58:28PM +0200, Vincent Guittot wrote:
> > update_blocked_averages() is called to periodiccally decay the stalled load
> > of idle CPUs and to sync all loads before running load balance.
> >
> > When cfs rq is idle, it trigs a load balance during pick_next_task_fair()
> > in order to potentially pull tasks and to use this newly idle CPU. This
> > load balance happens whereas prev task from another class has not been put
> > and its utilization updated yet. This may lead to wrongly account running
> > time as idle time for rt or dl classes.
> >
> > Test that no rt or dl task is running when updating their utilization in
> > update_blocked_averages().
> >
> > We still update rt and dl utilization instead of simply skipping them to
> > make sure that all metrics are synced when used during load balance.
> >
>
> Fixes: 371bf4273269 ("sched/rt: Add rt_rq utilization tracking")
> Fixes: 3727e0e16340 ("sched/dl: Add dl_rq utilization tracking")
>
> Right?

Yes

>
> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> > ---
> >  kernel/sched/fair.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 309c93f..a1babaf 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7262,6 +7262,7 @@ static void update_blocked_averages(int cpu)
> >  {
> >       struct rq *rq = cpu_rq(cpu);
> >       struct cfs_rq *cfs_rq, *pos;
> > +     const struct sched_class *curr_class = rq->curr->sched_class;
> >       struct rq_flags rf;
> >       bool done = true;
> >
> > @@ -7298,8 +7299,8 @@ static void update_blocked_averages(int cpu)
> >               if (cfs_rq_has_blocked(cfs_rq))
> >                       done = false;
> >       }
> > -     update_rt_rq_load_avg(rq_clock_task(rq), rq, 0);
> > -     update_dl_rq_load_avg(rq_clock_task(rq), rq, 0);
> > +     update_rt_rq_load_avg(rq_clock_task(rq), rq, curr_class == &rt_sched_class);
> > +     update_dl_rq_load_avg(rq_clock_task(rq), rq, curr_class == &dl_sched_class);
> >       update_irq_load_avg(rq, 0);
> >       /* Don't need periodic decay once load/util_avg are null */
> >       if (others_have_blocked(rq))
>
> Did you forget to update the second implementation of
> update_blocked_averages() ?

Yes. I have sent this version to quickly.
I'm going to send an update