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References: <20230205224318.2035646-1-qyousef@layalina.io> <20230205224318.2035646-3-qyousef@layalina.io>
In-Reply-To: <20230205224318.2035646-3-qyousef@layalina.io>
From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Tue, 7 Feb 2023 11:04:02 +0100
Message-ID: <CAKfTPtCf4+orEhYmFBg+tsMH7e5sV5zJZ1k8apjZkYwSAxAu+w@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] sched/uclamp: Ignore (util == 0) optimization in
 feec() when p_util_max = 0
To:     Qais Yousef <qyousef@layalina.io>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        linux-kernel@vger.kernel.org, Lukasz Luba <lukasz.luba@arm.com>,
        Wei Wang <wvw@google.com>, Xuewen Yan <xuewen.yan94@gmail.com>,
        Hank <han.lin@mediatek.com>,
        Jonathan JMChen <Jonathan.JMChen@mediatek.com>
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Precedence: bulk

On Sun, 5 Feb 2023 at 23:43, Qais Yousef <qyousef@layalina.io> wrote:
>
> find_energy_efficient_cpu() bails out early if effective util of the
> task is 0. When uclamp is being used, this could lead to wrong decisions
> when uclamp_max is set to 0. Cater for that.
>
> Fixes: d81304bc6193 ("sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early exit condition")
> Signed-off-by: Qais Yousef <qyousef@layalina.io>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 7a21ee74139f..a8c3d92ff3f6 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7374,7 +7374,7 @@ 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 (!uclamp_task_util(p, p_util_min, p_util_max) && p_util_max != 0)

The below should do the same without testing twice p_util_max:
uclamp_task_util(p, p_util_min, ULONG_MAX)


>                 goto unlock;
>
>         eenv_task_busy_time(&eenv, p, prev_cpu);
> --
> 2.25.1
>