linux-kernel - Re: [PATCH] cpufreq: schedutil: fix equation in comment

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Date:   Fri, 2 Aug 2019 15:19:02 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: schedutil: fix equation in comment

On Fri, 2 Aug 2019 at 12:46, Qais Yousef <qais.yousef@....com> wrote:
>
> scale_irq_capacity() call in schedutil_cpu_util() does
>
>         util *= (max - irq)
>         util /= max
>
> But the comment says
>
>         util *= (1 - irq)
>         util /= max
>
> Fix the comment to match what the scaling function does.
>
> Signed-off-by: Qais Yousef <qais.yousef@....com>

FWIW
Acked-by:  Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/sched/cpufreq_schedutil.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 636ca6f88c8e..e127d89d5974 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -259,9 +259,9 @@ unsigned long schedutil_cpu_util(int cpu, unsigned long util_cfs,
>          * irq metric. Because IRQ/steal time is hidden from the task clock we
>          * need to scale the task numbers:
>          *
> -        *              1 - irq
> -        *   U' = irq + ------- * U
> -        *                max
> +        *              max - irq
> +        *   U' = irq + --------- * U
> +        *                 max
>          */
>         util = scale_irq_capacity(util, irq, max);
>         util += irq;
> --
> 2.17.1
>