linux-kernel - Re: SD_LOAD

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Message-ID: <alpine.DEB.2.22.394.2010121330390.2901@hadrien>
Date:   Mon, 12 Oct 2020 13:31:12 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Julia Lawall <julia.lawall@...ia.fr>,
        Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org,
        Gilles Muller <Gilles.Muller@...ia.fr>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: SD_LOAD_BALANCE



On Mon, 12 Oct 2020, Peter Zijlstra wrote:

> On Sat, Oct 10, 2020 at 06:14:23PM +0200, Julia Lawall wrote:
> > Prior to v5.8 on my machine this was a rare event, because there were not
> > many of these background processes.  But in v5.8, the default governor for
> > Intel machines without the HWP feature was changed from intel_pstate to
> > intel_cpufreq.  The use of intel_cpufreq triggers very frequent kworkers on
> > all cores, which makes it much more likely that cores that are currently
> > idle, and are overall not at all overloaded, will have a higher load
> > average even with the waking thread deducted, than the core managing the
> > wakeup of the threads.
>
> Rafael, any idea what those kworkers are for, and can we get rid of
> them?

They execute the function intel_cpufreq_target defined in
drivers/cpufreq/intel_pstate.c

julia