linux-kernel - Re: [PATCH v3 2/3] sched/uclamp: Ignore (util == 0) optimization in feec() when p_util

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Message-ID: <CAKfTPtCAs5_LDkaxVBHW1wHZzpOHvgsL7Tz1PyDDqDHN2UU5Xw@mail.gmail.com>
Date:   Fri, 21 Jul 2023 11:57:19 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org, Lukasz Luba <lukasz.luba@....com>,
        Wei Wang <wvw@...gle.com>, Xuewen Yan <xuewen.yan94@...il.com>,
        Hank <han.lin@...iatek.com>,
        Jonathan JMChen <Jonathan.JMChen@...iatek.com>,
        Hongyan Xia <hongyan.xia2@....com>
Subject: Re: [PATCH v3 2/3] sched/uclamp: Ignore (util == 0) optimization in
 feec() when p_util_max = 0

On Mon, 17 Jul 2023 at 23:57, Qais Yousef <qyousef@...alina.io> wrote:
>
> find_energy_efficient_cpu() bails out early if effective util of the
> task is 0 as the delta at this point will be zero and there's nothing
> for EAS to do. When uclamp is being used, this could lead to wrong
> decisions when uclamp_max is set to 0. In this case the task is capped
> to performance point 0, but it is actually running and consuming energy
> and we can benefit from EAS energy calculations.
>
> Rework the condition so that it bails out for when util is actually 0 or
> uclamp_min is requesting a higher performance point.
>
> We can do that without needing to use uclamp_task_util(); remove it.
>
> Fixes: d81304bc6193 ("sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early exit condition")
> Signed-off-by: Qais Yousef (Google) <qyousef@...alina.io>

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

> ---
>  kernel/sched/fair.c | 18 +-----------------
>  1 file changed, 1 insertion(+), 17 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d489eece5a0d..c701f490ca4c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4348,22 +4348,6 @@ static inline unsigned long task_util_est(struct task_struct *p)
>         return max(task_util(p), _task_util_est(p));
>  }
>
> -#ifdef CONFIG_UCLAMP_TASK
> -static inline unsigned long uclamp_task_util(struct task_struct *p,
> -                                            unsigned long uclamp_min,
> -                                            unsigned long uclamp_max)
> -{
> -       return clamp(task_util_est(p), uclamp_min, uclamp_max);
> -}
> -#else
> -static inline unsigned long uclamp_task_util(struct task_struct *p,
> -                                            unsigned long uclamp_min,
> -                                            unsigned long uclamp_max)
> -{
> -       return task_util_est(p);
> -}
> -#endif
> -
>  static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
>                                     struct task_struct *p)
>  {
> @@ -7588,7 +7572,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
>         target = prev_cpu;
>
>         sync_entity_load_avg(&p->se);
> -       if (!uclamp_task_util(p, p_util_min, p_util_max))
> +       if (!task_util_est(p) && p_util_min == 0)
>                 goto unlock;
>
>         eenv_task_busy_time(&eenv, p, prev_cpu);
> --
> 2.25.1
>