linux-kernel - Re: [PATCH] sched/fair: fix runnable

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Message-ID: <xm26mu93u9l5.fsf@bsegall-linux.svl.corp.google.com>
Date:   Thu, 27 Feb 2020 11:13:58 -0800
From:   bsegall@...gle.com
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ben Segall <bsegall@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Phil Auld <pauld@...hat.com>, Parth Shah <parth@...ux.ibm.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Hillf Danton <hdanton@...a.com>, zhout@...aldi.net
Subject: Re: [PATCH] sched/fair: fix runnable_avg for throttled cfs

Vincent Guittot <vincent.guittot@...aro.org> writes:

> On Wed, 26 Feb 2020 at 20:04, <bsegall@...gle.com> wrote:
>>
>> Vincent Guittot <vincent.guittot@...aro.org> writes:
>>
>> > When a cfs_rq is throttled, its group entity is dequeued and its running
>> > tasks are removed. We must update runnable_avg with current h_nr_running
>> > and update group_se->runnable_weight with new h_nr_running at each level
>> > of the hierarchy.
>>
>> You'll also need to do this for task enqueue/dequeue inside of a
>> throttled hierarchy, I'm pretty sure.
>
> AFAICT, this is already done with patch "sched/pelt: Add a new
> runnable average signal" when task is enqueued/dequeued inside a
> throttled hierarchy

Right, I misread what exactly was going on.

>
>>
>> >
>> > Fixes: 9f68395333ad ("sched/pelt: Add a new runnable average signal")
>> > Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> > ---
>> > This patch applies on top of tip/sched/core
>> >
>> >  kernel/sched/fair.c | 10 ++++++++++
>> >  1 file changed, 10 insertions(+)
>> >
>> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> > index fcc968669aea..6d46974e9be7 100644
>> > --- a/kernel/sched/fair.c
>> > +++ b/kernel/sched/fair.c
>> > @@ -4703,6 +4703,11 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
>> >
>> >               if (dequeue)
>> >                       dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
>> > +             else {
>> > +                     update_load_avg(qcfs_rq, se, 0);
>> > +                     se_update_runnable(se);
>> > +             }
>> > +
>> >               qcfs_rq->h_nr_running -= task_delta;
>> >               qcfs_rq->idle_h_nr_running -= idle_task_delta;
>> >
>> > @@ -4772,6 +4777,11 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>> >               cfs_rq = cfs_rq_of(se);
>> >               if (enqueue)
>> >                       enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
>> > +             else {
>> > +                     update_load_avg(cfs_rq, se, 0);
>>
>>
>> > +                     se_update_runnable(se);
>> > +             }
>> > +
>> >               cfs_rq->h_nr_running += task_delta;
>> >               cfs_rq->idle_h_nr_running += idle_task_delta;