linux-kernel - Re: [PATCH v2] cpufreq: schedutil: rate limits for SCHED

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Date:   Wed, 28 Feb 2018 12:15:56 +0100
From:   Claudio Scordino <claudio@...dence.eu.com>
To:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] cpufreq: schedutil: rate limits for SCHED_DEADLINE

Dear Rafael, dear Viresh,

Il 28/02/2018 12:06, Claudio Scordino ha scritto:
> When the SCHED_DEADLINE scheduling class increases the CPU utilization,
> we should not wait for the rate limit, otherwise we may miss some
> deadline.
> 
> Tests using rt-app on Exynos5422 with up to 10 SCHED_DEADLINE tasks have
> shown reductions of even 10% of deadline misses with a negligible
> increase of energy consumption (measured through Baylibre Cape).

As a follow up of the previous thread, I've put some figures here: https://gist.github.com/claudioscordino/d4a10e8b3ceac419fb0c8b552db19806

In some cases, I've noticed the patch to even reduce the energy consumption (due to a mix of factors plus DL tasks entering the inactive state sooner).

I've also tried to create the "ramp-up" scenario by allocating 10 DL tasks on the same core, but it didn't produce any significant increase of consumption.

IMHO, the overall behavior looks better.

Best regards,

              Claudio