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

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Date:   Fri, 17 Feb 2017 13:48:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        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 Fri, Feb 17, 2017 at 01:15:56PM +0100, Rafael J. Wysocki wrote:
> On Thursday, February 16, 2017 01:36:05 PM Peter Zijlstra wrote:
> > 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.
> 
> OK
> 
> Does this mean that running governor computations every time its callback
> is invoked by the scheduler would be fine?

I'd say yes right up till the point someone reports a regression ;-)