linux-kernel - Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to SCHED

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Date:   Fri, 11 Nov 2016 15:32:04 +0100
From:   Tommaso Cucinotta <tommaso.cucinotta@...up.it>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <Juri.Lelli@....com>,
        Robin Randhawa <robin.randhawa@....com>,
        Steve Muckle <smuckle.linux@...il.com>
Subject: Re: [PATCH 2/3] cpufreq: schedutil: move slow path from workqueue to
 SCHED_FIFO task

Hi,

On 11/11/2016 11:22, Viresh Kumar wrote:
> If slow path frequency changes are conducted in a SCHED_OTHER context
> then they may be delayed for some amount of time, including
> indefinitely, when real time or deadline activity is taking place.
>
> Move the slow path to a real time kernel thread. In the future the
> thread should be made SCHED_DEADLINE.

would you have an insight, as to what runtime/deadline/period to set, and/or
what specific timing constraints you'd like to set, just for this cpufreq
slowpath work?

> The RT priority is arbitrarily set
> to 50 for now.
[...]
> +	struct sched_param param = { .sched_priority = 50 };

won't you have a tunable here? (sysctl?)

Thanks,

	T.
-- 
Tommaso Cucinotta, Computer Engineering PhD
Associate Professor at the Real-Time Systems Laboratory (ReTiS)
Scuola Superiore Sant'Anna, Pisa, Italy
http://retis.sssup.it/people/tommaso