linux-kernel - Re: [PATCH] sched: cpufreq_schedutil: restore cached freq when next

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Message-ID: <CAJZ5v0jaftAQv9-=5YucNnm__Z7NWRWmN2mCO07i0ZhV9K5EsQ@mail.gmail.com>
Date:   Mon, 19 Oct 2020 17:39:50 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Wei Wang <wvw@...gle.com>
Cc:     Wei Wang <wei.vince.wang@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Quentin Perret <qperret@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: cpufreq_schedutil: restore cached freq when next_f
 is not changed

On Fri, Oct 16, 2020 at 8:17 PM Wei Wang <wvw@...gle.com> wrote:
>
> We have the raw cached freq to reduce the chance in calling cpufreq
> driver where it could be costly in some arch/SoC.
>
> Currently, the raw cached freq will be reset when next_f is changed for
> correctness. This patch changes it to maintain the cached value instead
> of dropping it to honor the purpose of the cached value.
>
> This is adapted from https://android-review.googlesource.com/1352810/
>
> Signed-off-by: Wei Wang <wvw@...gle.com>
> ---
>  kernel/sched/cpufreq_schedutil.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 5ae7b4e6e8d6..e254745a82cb 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -441,6 +441,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>         unsigned long util, max;
>         unsigned int next_f;
>         bool busy;
> +       unsigned int cached_freq = sg_policy->cached_raw_freq;
>
>         sugov_iowait_boost(sg_cpu, time, flags);
>         sg_cpu->last_update = time;
> @@ -464,8 +465,8 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>         if (busy && next_f < sg_policy->next_freq) {
>                 next_f = sg_policy->next_freq;
>
> -               /* Reset cached freq as next_freq has changed */
> -               sg_policy->cached_raw_freq = 0;
> +               /* Restore cached freq as next_freq has changed */
> +               sg_policy->cached_raw_freq = cached_freq;
>         }
>
>         /*
> --

Applied as 5.10-rc material with edited subject and rewritten changelog.

Thanks!