From: Vincent Guittot <vincent.guittot@linaro.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
SoC Team <soc@kernel.org>, arm-soc <arm@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] ARM: config: multi_v7 Use schedutil cpufreq
Date: Fri, 27 Mar 2020 09:06:12 +0100 [thread overview]
Message-ID: <CAKfTPtDU9rOaq69YNMSSwQ3iK63jbROAUnSxETqqCyDOLFB-jA@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdaYo0w8Zy4MjxC9Hqhyv7rhOMzSf_t1ZqWnyXW=9Q7iJg@mail.gmail.com>
On Thu, 26 Mar 2020 at 23:08, Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Wed, Mar 25, 2020 at 5:28 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > On Mon, Mar 2, 2020 at 5:22 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> > > FWIW, I have tried something similar for arm64 earlier.
> > >
> > > https://lore.kernel.org/lkml/af12e002bc165844101830c0eb00e283b536a879.1510813288.git.viresh.kumar@linaro.org/
> >
> > I've dropped this one and not applied it for now after rereading the old thread.
> > If there is a broader agreement on what the default should be, please
> > collect more Acks and we can apply whatever you come up with.
>
> I think there is a more compelling argument: if I understand correctly
> the energy aware scheduling and HMP on big.LITTLE only works
> correctly if schedutil is used as cpufreq governor (correct Vincent, Viresh?)
EAS is disabled while building scheduler toology if schedutil is not
the cpufreq governor
Quoting from kernel/sched/topology.c:
/*
* EAS can be used on a root domain if it meets all the following conditions:
* 1. an Energy Model (EM) is available;
* 2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy.
* 3. no SMT is detected.
* 4. the EM complexity is low enough to keep scheduling overheads low;
* 5. schedutil is driving the frequency of all CPUs of the rd;
*
>
> That would make the default multi_v7 unusable (or misbehaving)
> on e.g. Vexpress TC2.
>
> Thus I suspect the Vexpress and other machines using HMP
> and big.LITTLE should just select
> CPU_FREQ_DEFAULT_GOV_SCHEDUTIL in their Kconfig.
>
> That will of course make it percolate up to multi_v7 by default
> as well.
>
> If more magic configs are necessary to select to make a TC2
> work properly I'd like to know these as well so we can just select
> them all by default also for these targets.
>
> Yours,
> Linus Walleij
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prev parent reply other threads:[~2020-03-27 8:06 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-29 21:02 [PATCH] ARM: config: multi_v7 Use schedutil cpufreq Linus Walleij
2020-03-02 4:22 ` Viresh Kumar
2020-03-25 16:27 ` Arnd Bergmann
2020-03-26 22:08 ` Linus Walleij
2020-03-27 5:07 ` Viresh Kumar
2020-03-27 8:06 ` Vincent Guittot [this message]
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