linux-kernel - Re: [PATCH V3 2/2] sched/uclamp: Align uclamp and util

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Message-ID: <CAKfTPtBbBL=FNCO8bzm-2p6n6o2omzUNfXuUz-s=4nW_E3ShYQ@mail.gmail.com>
Date: Fri, 18 Apr 2025 17:00:41 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: dietmar.eggemann@....com, mingo@...hat.com, peterz@...radead.org, 
	juri.lelli@...hat.com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, vschneid@...hat.com, hongyan.xia2@....com, 
	linux-kernel@...r.kernel.org, ke.wang@...soc.com, di.shen@...soc.com, 
	xuewen.yan94@...il.com, kprateek.nayak@....com, kuyo.chang@...iatek.com, 
	juju.sung@...iatek.com, qyousef@...alina.io
Subject: Re: [PATCH V3 2/2] sched/uclamp: Align uclamp and util_est and call
 before freq update

On Thu, 17 Apr 2025 at 06:36, Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> The commit dfa0a574cbc47 ("sched/uclamg: Handle delayed dequeue")
> has add the sched_delayed check to prevent double uclamp_dec/inc.
> However, it put the uclamp_rq_inc() after enqueue_task().
> This may lead to the following issues:
> When a task with uclamp goes through enqueue_task() and could trigger
> cpufreq update, its uclamp won't even be considered in the cpufreq
> update. It is only after enqueue will the uclamp be added to rq
> buckets, and cpufreq will only pick it up at the next update.
> This could cause a delay in frequency updating. It may affect
> the performance(uclamp_min > 0) or power(uclamp_max < 1024).
>
> So, just like util_est, put the uclamp_rq_inc() before enqueue_task().
> And as for the sched_delayed_task, same as util_est, using the
> sched_delayed flag to prevent inc the sched_delayed_task's uclamp,
> using the ENQUEUE_DELAYED flag to allow inc the sched_delayed_task's uclamp
> which is being woken up.
>
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>

Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>


> ---
> v3:
> - rework the commit message;
> - remove the util_est change;
> v2:
> - simply the util-est's en/dequeue check;
> ---
>  kernel/sched/core.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c81cf642dba0..0f4ab0c17c58 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1752,7 +1752,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
>         }
>  }
>
> -static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
> +static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p, int flags)
>  {
>         enum uclamp_id clamp_id;
>
> @@ -1768,7 +1768,8 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
>         if (unlikely(!p->sched_class->uclamp_enabled))
>                 return;
>
> -       if (p->se.sched_delayed)
> +       /* Only inc the delayed task which being woken up. */
> +       if (p->se.sched_delayed && !(flags & ENQUEUE_DELAYED))
>                 return;
>
>         for_each_clamp_id(clamp_id)
> @@ -2036,7 +2037,7 @@ static void __init init_uclamp(void)
>  }
>
>  #else /* !CONFIG_UCLAMP_TASK */
> -static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
> +static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p, int flags) { }
>  static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
>  static inline void uclamp_fork(struct task_struct *p) { }
>  static inline void uclamp_post_fork(struct task_struct *p) { }
> @@ -2072,12 +2073,14 @@ void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
>         if (!(flags & ENQUEUE_NOCLOCK))
>                 update_rq_clock(rq);
>
> -       p->sched_class->enqueue_task(rq, p, flags);
>         /*
> -        * Must be after ->enqueue_task() because ENQUEUE_DELAYED can clear
> -        * ->sched_delayed.
> +        * Can be before ->enqueue_task() because uclamp considers the
> +        * ENQUEUE_DELAYED task before its ->sched_delayed gets cleared
> +        * in ->enqueue_task().
>          */
> -       uclamp_rq_inc(rq, p);
> +       uclamp_rq_inc(rq, p, flags);
> +
> +       p->sched_class->enqueue_task(rq, p, flags);
>
>         psi_enqueue(p, flags);
>
> --
> 2.25.1
>
>