linux-kernel - Re: [PATCH] cpufreq: schedutil: govern how frequently we change frequency with rate

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Message-ID: <20170216123605.GA6515@twins.programming.kicks-ass.net>
Date:   Thu, 16 Feb 2017 13:36:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>, linaro-kernel@...ts.linaro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] cpufreq: schedutil: govern how frequently we change
 frequency with rate_limit

On Thu, Feb 16, 2017 at 03:42:10PM +0530, Viresh Kumar wrote:
> But when I discussed this with Vincent, he suggested that it may not be required
> at all as the scheduler (with the helped of "decayed") doesn't call into
> schedutil too often, i.e. at least 1 ms. And if the CPUs are stable enough (i.e.
> no interruptions to the running task), we wouldn't reevaluate before the next
> tick.

There are still the attach/detach callers to cfs_rq_util_change() that
kick in for fork/exit and migration.

But yes, barring those we shouldn't end up calling it at silly rates.