linux-kernel - Re: [PATCH v10 8/9] sched/fair: Add latency list

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Message-ID: <CAKfTPtDQ0hgiqdO7ywUEw3htpiBS3NxWMxXL9LqmBpA8E25quw@mail.gmail.com>
Date:   Tue, 21 Feb 2023 16:42:38 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
        cgroups@...r.kernel.org, qyousef@...alina.io,
        chris.hyser@...cle.com, patrick.bellasi@...bug.net,
        David.Laight@...lab.com, pjt@...gle.com, pavel@....cz,
        tj@...nel.org, qperret@...gle.com, tim.c.chen@...ux.intel.com,
        joshdon@...gle.com, timj@....org, kprateek.nayak@....com,
        yu.c.chen@...el.com, youssefesmat@...omium.org,
        joel@...lfernandes.org
Subject: Re: [PATCH v10 8/9] sched/fair: Add latency list

On Tue, 21 Feb 2023 at 16:12, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Jan 13, 2023 at 03:12:33PM +0100, Vincent Guittot wrote:
> > @@ -12552,8 +12634,15 @@ int sched_group_set_latency(struct task_group *tg, s64 latency)
> >
> >       for_each_possible_cpu(i) {
> >               struct sched_entity *se = tg->se[i];
> > +             struct rq *rq = cpu_rq(i);
> > +             struct rq_flags rf;
> > +
> > +             rq_lock_irqsave(rq, &rf);
> >
> > +             __dequeue_latency(se->cfs_rq, se);
> >               WRITE_ONCE(se->latency_offset, latency);
> > +
> > +             rq_unlock_irqrestore(rq, &rf);
> >       }
>
> This seems asymmetric; maybe something like:
>
>         queued = __dequeue_latency(..);
>         WRITE_ONCE(...);
>         if (queued)
>                 __enqueue_latency(...);
>
> ?

Fair enough