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

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Date:   Fri, 5 Feb 2021 12:42:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Michael Larabel <Michael@...ronix.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        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 Fri, Feb 5, 2021 at 12:04 AM Michael Larabel <Michael@...ronix.com> wrote:
>
> On 2/4/21 7:40 AM, Rafael J. Wysocki wrote:
> > 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.
>
>
> Everything continues looking good in running this patch on a variety of
> AMD Zen2/Zen3 systems.
>
> As Giovanni has been focusing on EPYC testing, I have been running
> several Ryzen laptops/desktop for more exposure and there it's looking
> very good. On a Ryzen 9 5900X[1] when looking at this latest patch
> against current 5.11 Git and 5.10, the performance is recovered and in
> some cases better off now than 5.10 with Schedutil. No anomalies there
> and with other Zen 2/3 desktops and Zen 2 notebook the performance
> relative to 5.10 is comparable or in some cases better while all
> indications point to the 5.11 regression being addressed. Some of the
> slower systems still finishing up but no unexpected results yet and
> likely just redundant testing at this point.
>
> Tests on EPYC hardware has also been looking good. With some 44 tests on
> an EPYC 7F72 2P setup[2] when taking the geometric mean of all the data
> finding it rightly in line with the prior patch from Giovanni. EPYC 7702
> and EPYC 7F52 1P performance similarly showing no regression any longer
> with the patched kernel. This patch also seemed to help CPUFreq ondemand
> performance improve as well in some cases.
>
> Will advise if hitting anything unexpected with the remainder of the
> testing but all is looking solid at this point and a definite
> improvement over the current 5.11 Git state.
>
> Tested-by: Michael Larabel <Michael@...ronix.com>

Thank you for all of the verification work, much appreciated!

> [1] https://openbenchmarking.org/result/2102048-PTS-RYZEN95920 (5.10
> stable vs. 5.11 Git vs. patched.)
> [2] https://openbenchmarking.org/result/2102048-HA-AMDEPYC7F37
> (Giovanni's earlier patch against this new patch, compared to unpatched
> Linux 5.11 Git and then Linux 5.11 with CPUfreq performance governor.)