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

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Date:   Sun, 20 Aug 2023 14:52:31 +0100
From:   Qais Yousef <qyousef@...alina.io>
To:     Vincent Guittot <vincent.guittot@...aro.org>
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 07/21/23 11:57, Vincent Guittot wrote:
> 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>

Thanks Vincent!

Ping in case this has fallen through the cracks. I hope it's good to be picked
up now.


Thanks!

--
Qais Yousef

> 
> > ---
> >  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
> >