linux-kernel - Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to sugov

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Date:   Wed, 16 Nov 2022 13:17:47 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        Sam Wu <wusamuel@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        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>,
        Valentin Schneider <vschneid@...hat.com>,
        "Isaac J . Manjarres" <isaacmanjarres@...gle.com>,
        kernel-team@...roid.com,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to sugov_policy"

On Wed, Nov 16, 2022 at 12:43 PM Lukasz Luba <lukasz.luba@....com> wrote:
>
>
>
> On 11/15/22 22:35, Saravana Kannan wrote:
> > On Thu, Nov 10, 2022 at 11:57 AM Sam Wu <wusamuel@...gle.com> wrote:
> >>
> >> This reverts commit 6d5afdc97ea71958287364a1f1d07e59ef151b11.
> >>
> >> On a Pixel 6 device, it is observed that this commit increases
> >> latency by approximately 50ms, or 20%, in migrating a task
> >> that requires full CPU utilization from a LITTLE CPU to Fmax
> >> on a big CPU. Reverting this change restores the latency back
> >> to its original baseline value.
> >>
> >> Fixes: 6d5afdc97ea7 ("cpufreq: schedutil: Move max CPU capacity to sugov_policy")
> >> Cc: Lukasz Luba <lukasz.luba@....com>
> >> Cc: Saravana Kannan <saravanak@...gle.com>
> >> Cc: Isaac J. Manjarres <isaacmanjarres@...gle.com>
> >> Signed-off-by: Sam Wu <wusamuel@...gle.com>
> >
> > Rafael, can we pick this up please?
> >
> > Lukasz, no objections to the idea itself, but it's causing regression
> > and we'd like to revert and then fix it.
>
> If you see this in mainline kernel, then I'm fine with reverting it.

OK, I'll wait for the confirmation of this.

> Then I will have to trace why this CPU capacity value can change over
> time in mainline kernel (while it shouldn't, because we register the
> cpufreq policy and the governor later, after we calculate the capacity
> in arch_topology.c). Maybe something has changed in mainline in the
> meantime in this CPU capacity setup code, which caused this side effect.
>
> I know that android-mainline has some different setup code for those
> custom vendor governors. I just want to eliminate this bit and be on the
> same page.