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Date: Thu, 21 Jan 2021 02:09:14 +0100 From: Giovanni Gherdovich <ggherdovich@...e.cz> To: Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Rafael J . Wysocki" <rjw@...ysocki.net>, Viresh Kumar <viresh.kumar@...aro.org> Cc: 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>, x86@...nel.org, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org Subject: Re: [PATCH] x86,sched: On AMD EPYC set freq_max = max_boost in schedutil invariant formula On Thu, 2021-01-21 at 01:35 +0100, Giovanni Gherdovich wrote: > Phoronix.com discovered a severe performance regression on AMD APYC > introduced on schedutil [see link 1] by the following commits from v5.11-rc1 > > commit 41ea667227ba ("x86, sched: Calculate frequency invariance for AMD systems") > commit 976df7e5730e ("x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC") > > Furthermore commit db865272d9c4 ("cpufreq: Avoid configuring old governors as > default with intel_pstate") from v5.10 made it extremely easy to default to > schedutil even if the preferred driver is acpi_cpufreq. Distros are likely to > build both intel_pstate and acpi_cpufreq on x86, and the presence of the > former removes ondemand from the defaults. This situation amplifies the > visibility of the bug we're addressing. > > [link 1] https://www.phoronix.com/scan.php?page=article&item=linux511-amd-schedutil&num=1 > > 1. PROBLEM DESCRIPTION : over-utilization and schedutil > 2. PROPOSED SOLUTION : raise freq_max in schedutil formula > 3. DATA TABLE : image processing benchmark > 4. ANALYSIS AND COMMENTS : with over-utilization, freq-invariance is lost I've sent this patch twice by mistake, sorry about that. In case it is of interest, I've shared some plots made while studying this regression in a bugzilla entry: https://bugzilla.kernel.org/show_bug.cgi?id=211305 Thanks, Giovanni
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