linux-kernel - Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core

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Date:   Fri, 23 Oct 2020 09:03:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Giovanni Gherdovich <ggherdovich@...e.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Mel Gorman <mgorman@...e.de>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Julia Lawall <julia.lawall@...ia.fr>,
        Ingo Molnar <mingo@...hat.com>,
        kernel-janitors@...r.kernel.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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org,
        Valentin Schneider <valentin.schneider@....com>,
        Gilles Muller <Gilles.Muller@...ia.fr>,
        srinivas.pandruvada@...ux.intel.com,
        Linux PM <linux-pm@...r.kernel.org>,
        Len Brown <len.brown@...el.com>, thomas.lendacky@....com,
        puwen@...on.cn, yazen.ghannam@....com, kim.phillips@....com,
        suravee.suthikulpanit@....com
Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core

On Thu, Oct 22, 2020 at 10:10:35PM +0200, Giovanni Gherdovich wrote:
> * for the AMD EPYC machines we haven't yet implemented frequency invariant
>   accounting, which might explain why schedutil looses to ondemand on all
>   the benchmarks.

Right, I poked the AMD people on that a few times, but nothing seems to
be forthcoming :/ Tom, any way you could perhaps expedite the matter?

In particular we're looking for some X86_VENDOR_AMD/HYGON code to run in

  arch/x86/kernel/smpboot.c:init_freq_invariance()

The main issue is finding a 'max' frequency that is not the absolute max
turbo boost (this could result in not reaching it very often) but also
not too low such that we're always clipping.

And while we're here, IIUC AMD is still using acpi_cpufreq, but AFAIK
the chips have a CPPC interface which could be used instead. Is there
any progress on that?