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Date:   Thu, 21 Jan 2021 02:09:14 +0100
From:   Giovanni Gherdovich <>
To:     Borislav Petkov <>, Ingo Molnar <>,
        Peter Zijlstra <>,
        "Rafael J . Wysocki" <>,
        Viresh Kumar <>
Cc:     Jon Grimm <>,
        Nathan Fontenot <>,
        Yazen Ghannam <>,
        Thomas Lendacky <>,
        Suthikulpanit Suravee <>,
        Mel Gorman <>,
        Pu Wen <>, Juri Lelli <>,
        Vincent Guittot <>,
        Dietmar Eggemann <>,,,,
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:
> 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]
> 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:


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