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

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Message-ID: <4853380.1xLm2rt1ou@aspire.rjw.lan>
Date:   Mon, 20 Feb 2017 14:49:18 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.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 Monday, February 20, 2017 03:28:03 PM Viresh Kumar wrote:
> On 17-02-17, 13:48, Peter Zijlstra wrote:
> > 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 ;-)
> 
> @Rafael: Do you want me to send a V2 with the changes you suggested in
> commit log?

Yes, in general, but I have more suggestions regarding that. :-)

I'll send them shortly.

Thanks,
Rafael