linux-kernel - Re: [PATCH v3 1/1] x86,sched: On AMD EPYC set freq_max = max

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Message-ID: <CAJZ5v0jzhVJ-8iVfhkFHBdJf1pYAMtC=1JhuTn14vWtZUwJoAg@mail.gmail.com>
Date:   Thu, 4 Feb 2021 14:40:30 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Michael Larabel <Michael@...ronix.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        "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 v3 1/1] x86,sched: On AMD EPYC set freq_max = max_boost in
 schedutil invariant formula

On Thu, Feb 4, 2021 at 12:36 AM Michael Larabel <Michael@...ronix.com> wrote:
>
> On 2/3/21 12:25 PM, Rafael J. Wysocki wrote:
> > On Wednesday, February 3, 2021 3:11:37 PM CET Rafael J. Wysocki wrote:
> >> On Wed, Feb 3, 2021 at 2:53 PM Giovanni Gherdovich <ggherdovich@...e.cz> wrote:
> >> [cut]
> >>
> >>> Fixes: 41ea667227ba ("x86, sched: Calculate frequency invariance for AMD systems")
> >>> Fixes: 976df7e5730e ("x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC")
> >>> Reported-by: Michael Larabel <Michael@...ronix.com>
> >>> Tested-by: Michael Larabel <Michael@...ronix.com>
> >>> Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
> >>> ---
> >>>   drivers/cpufreq/acpi-cpufreq.c   | 61 ++++++++++++++++++++++++++++++--
> >>>   drivers/cpufreq/cpufreq.c        |  3 ++
> >>>   include/linux/cpufreq.h          |  5 +++
> >>>   kernel/sched/cpufreq_schedutil.c |  8 +++--
> >> I don't really think that it is necessary to modify schedutil to
> >> address this issue.
> > So below is a prototype of an alternative fix for the issue at hand.
> >
> > I can't really test it here, because there's no _CPC in the ACPI tables of my
> > test machines, so testing it would be appreciated.  However, AFAICS these
> > machines are affected by the performance issue related to the scale-invariance
> > when they are running acpi-cpufreq, so what we are doing here is not entirely
> > sufficient.
>
>
> I have benchmarks running on several Ryzen and EPYC systems with this
> patch. The full batch of tests won't be done until tomorrow, but in
> looking at the data so far from an AMD EPYC 7F72 2P server over the past
> few hours, this patch does provide fairly comparable numbers to
> Giovanni's patch. There were a few outliers so far but waiting to see
> with the complete set of results. At the very least it's clear enough
> already this new patch is at least an improvement over the current 5.11
> upstream state with schedutil on AMD.

Thanks for the feedback, much appreciated!

Let me submit the patch properly, then.