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

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Message-ID: <4a0db95a-1ba2-21f5-5c9d-67b9f82ed130@amd.com>
Date:   Fri, 23 Oct 2020 12:46:35 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        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>, puwen@...on.cn,
        yazen.ghannam@....com, kim.phillips@....com,
        suravee.suthikulpanit@....com,
        "Fontenot, Nathan" <Nathan.Fontenot@....com>
Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core

On 10/23/20 2:03 AM, Peter Zijlstra wrote:
> 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?

Adding Nathan to the thread to help out here.

Thanks,
Tom

> 
> 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?
>