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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 16 Nov 2022 13:17:47 +0100
Message-ID: <CAJZ5v0hpDiQUoWZO7YzhU2ymyyNK4uwZrS8nuwyrs2rjNOO4SA@mail.gmail.com>
Subject: Re: [PATCH v1] Revert "cpufreq: schedutil: Move max CPU capacity to sugov_policy"
To:     Lukasz Luba <lukasz.luba@arm.com>
Cc:     Saravana Kannan <saravanak@google.com>,
        Sam Wu <wusamuel@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        "Isaac J . Manjarres" <isaacmanjarres@google.com>,
        kernel-team@android.com,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
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On Wed, Nov 16, 2022 at 12:43 PM Lukasz Luba <lukasz.luba@arm.com> wrote:
>
>
>
> On 11/15/22 22:35, Saravana Kannan wrote:
> > On Thu, Nov 10, 2022 at 11:57 AM Sam Wu <wusamuel@google.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@arm.com>
> >> Cc: Saravana Kannan <saravanak@google.com>
> >> Cc: Isaac J. Manjarres <isaacmanjarres@google.com>
> >> Signed-off-by: Sam Wu <wusamuel@google.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.