linux-kernel - Re: [PATCH] sched/uclamp: Let each sched

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Message-ID: <CAB8ipk_627GF+TV5u=6DK_3aRUHW8qGYwmN+KXMq_Cg-+Say1Q@mail.gmail.com>
Date: Thu, 6 Mar 2025 20:01:41 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Hongyan Xia <hongyan.xia2@....com>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, 
	Vincent Guittot <vincent.guittot@...aro.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>, 
	Andrea Righi <arighi@...dia.com>, Changwoo Min <changwoo@...lia.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/uclamp: Let each sched_class handle uclamp

On Thu, Mar 6, 2025 at 2:24 AM Dietmar Eggemann
<dietmar.eggemann@....com> wrote:
>
> On 27/02/2025 14:54, Hongyan Xia wrote:
>
> [...]
>
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 857808da23d8..7e5a653811ad 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6941,8 +6941,10 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> >        * Let's add the task's estimated utilization to the cfs_rq's
> >        * estimated utilization, before we update schedutil.
> >        */
> > -     if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & ENQUEUE_RESTORE))))
> > +     if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & ENQUEUE_RESTORE)))) {
> > +             uclamp_rq_inc(rq, p);
> >               util_est_enqueue(&rq->cfs, p);
> > +     }
>
> So you want to have p uclamp-enqueued so that its uclamp_min value
> counts for the cpufreq_update_util()/cfs_rq_util_change() calls later in
> enqueue_task_fair?
>
>   if (p->in_iowait)
>     cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
>
>   enqueue_entity() -> update_load_avg() -> cfs_rq_util_change() ->
>   cpufreq_update_util()
>
> But if you do this before requeue_delayed_entity() (1) you will not
> uclamp-enqueue p which got his ->sched_delayed just cleared in (1)?
>

Could we change to the following:

when enqueue:

-     if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags
& ENQUEUE_RESTORE))))
+     if (!(p->se.sched_delayed && !(flags & ENQUEUE_DELAYED)))
+             uclamp_rq_inc(rq, p);
               util_est_enqueue(&rq->cfs, p);
 +     }


when dequeue:

-       if (!(p->se.sched_delayed && (task_on_rq_migrating(p) ||
(flags & DEQUEUE_SAVE))))
+       if (!p->se.sched_delayed) {
+               uclamp_rq_dec(rq, p);
                util_est_dequeue(&rq->cfs, p);
+       }


> [...]
>