linux-kernel - Re: [RFC PATCH] sched/util_est: Do not sub the delayed-task's util-est

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Message-ID: <CAB8ipk8FX=zhBo0vHPC8MEHMEJKsa+E9J081mzJMLZU_8-U78w@mail.gmail.com>
Date: Fri, 21 Mar 2025 14:44:12 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, vincent.guittot@...aro.org, mingo@...hat.com, 
	peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.co, 
	linux-kernel@...r.kernel.org, hongyan.xia2@....com, qyousef@...alina.io, 
	ke.wang@...soc.com, di.shen@...soc.com
Subject: Re: [RFC PATCH] sched/util_est: Do not sub the delayed-task's util-est

Hi hongyan

On Wed, Mar 19, 2025 at 9:33 PM Dietmar Eggemann
<dietmar.eggemann@....com> wrote:
>
> On 14/03/2025 10:09, Xuewen Yan wrote:
> > In cpu_util_without, When the task is in rq, we should
> > sub the task's util_est, however, the delayed_task->on_rq
> > is true, however, the delayed_task's util had been sub
> > when sleep, so there is no need to sub the delayed task's
> > util-est. So add the checking of delayed-task.
> >
> > On the other hand, as said in [1], the logic of util_est's
> > enqueue/dequeue could be simplified.
> > So simplify it by aligning with the conditions of uclamp.
>
> This flag simplification looks good to me.
>
> IMHO, you should submit this with the uclamp change so that we can call
> uclamp_rq_inc() before p->sched_class->enqueue_task(). To make sure the
> task which is enqueued with 'flags & ENQUEUE_DELAYED' is considered for
> cpufreq_update_util() in enqueue_task_fair() (Hongyan's finding in
> https://lkml.kernel.org/r/84441660bef0a5e67fd09dc3787178d0276dad31.1740664400.git.hongyan.xia2@arm.com)
>
> I would prefer the less invasive fix you presented here:
>
> https://lkml.kernel.org/r/CAB8ipk9LpbiUDnbcV6+59+Sa=Ai7tFzO===mpLD3obNdV4=J-A@mail.gmail.com
>
> since uclamp is already a core thing (fair + rt), it works for current
> max aggregation and it's less invasive.
>

Since the uclamp's enqueue is affecting performance, could we fix the
uclamp-enqueue issue first?
Need I to send the patch-v2 base the
https://lore.kernel.org/all/CAB8ipk9LpbiUDnbcV6+59+Sa=Ai7tFzO===mpLD3obNdV4=J-A@mail.gmail.com/T/#mb32d7675beda5cadc35a3c04cddebc39580c718b
?
As for whether we need to distinguish sched-class, can we discuss that later?

Thanks!

> [...]
>
> > @@ -8037,7 +8037,8 @@ cpu_util(int cpu, struct task_struct *p, int dst_cpu, int boost)
> >                */
> >               if (dst_cpu == cpu)
> >                       util_est += _task_util_est(p);
> > -             else if (p && unlikely(task_on_rq_queued(p) || current == p))
> > +             else if (p && unlikely(current == p ||
> > +                      (task_on_rq_queued(p) && !p->se.sched_delayed)))
> >                       lsub_positive(&util_est, _task_util_est(p));
>
> cpu_util(..., p != NULL, ...) is only used for select_task_rq_fair().
> IMHO p->se.sched_delayed is not set there.

Hi Dietmar,
You're right, there's really no need to add extra conditions here at the moment.

Thanks!