linux-kernel - Re: [PATCH v2 1/1] x86,sched: On AMD EPYC set freq_max = max

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Date:   Wed, 03 Feb 2021 10:56:15 +0100
From:   Giovanni Gherdovich <ggherdovich@...e.cz>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Jon Grimm <Jon.Grimm@....com>,
        Nathan Fontenot <Nathan.Fontenot@....com>,
        Yazen Ghannam <Yazen.Ghannam@....com>,
        Thomas Lendacky <Thomas.Lendacky@....com>,
        Suthikulpanit Suravee <Suravee.Suthikulpanit@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pu Wen <puwen@...on.cn>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Michael Larabel <Michael@...ronix.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] x86,sched: On AMD EPYC set freq_max = max_boost
 in schedutil invariant formula

On Tue, 2021-02-02 at 20:11 +0100, Rafael J. Wysocki wrote:
> On Tue, Feb 2, 2021 at 7:45 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > 
> > On Tue, Jan 26, 2021 at 5:19 PM Giovanni Gherdovich <ggherdovich@...e.cz> wrote:
> > > 
> > >
> > > cpufreq core asks the driver what's the f_max. What's the answer?
> > > 
> > > intel_pstate says: 1C
> > 
> > Yes, unless turbo is disabled, in which case it is P0.
> 
> BTW, and that actually is quite important, the max_freq reported by
> intel_pstate doesn't matter for schedutil after the new ->adjust_perf
> callback has been added, because that doesn't even use the frequency.
> 
> So, as a long-term remedy, it may just be better to implement
> ->adjust_perf in acpi_cpufreq().

Thanks for pointing this out.

I agree that in the long term adding ->adjust_perf to acpi_cpufreq is
the best solution.

Yet for this submission, considering it's late in the 5.11 cycle,
the patch I propose is a reasonable candidate: the footprint is small and
it's gone through a fair amount of testing.


Thanks,
Giovanni