linux-kernel - Re: [PATCH RFC 4/8] sched/cpufreq_schedutil: split utilization signals

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Date:   Wed, 24 May 2017 09:01:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Juri Lelli <juri.lelli@....com>, mingo@...hat.com,
        viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, tglx@...utronix.de,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        luca.abeni@...tannapisa.it, claudio@...dence.eu.com,
        tommaso.cucinotta@...tannapisa.it, bristot@...hat.com,
        mathieu.poirier@...aro.org, tkjos@...roid.com, joelaf@...gle.com,
        andresoportus@...gle.com, morten.rasmussen@....com,
        dietmar.eggemann@....com, patrick.bellasi@....com,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH RFC 4/8] sched/cpufreq_schedutil: split utilization
 signals

On Wed, May 24, 2017 at 01:30:36AM +0200, Rafael J. Wysocki wrote:
> On Tuesday, May 23, 2017 09:29:27 PM Peter Zijlstra wrote:
> > On Tue, May 23, 2017 at 09:53:47AM +0100, Juri Lelli wrote:
> > > To be able to treat utilization signals of different scheduling classes
> > > in different ways (e.g., CFS signal might be stale while DEADLINE signal
> > > is never stale by design) we need to split sugov_cpu::util signal in two:
> > > util_cfs and util_dl.
> > > 
> > > This patch does that by also changing sugov_get_util() parameter list.
> > > After this change aggregation of the different signals has to be performed
> > > by sugov_get_util() users (so that they can decide what to do with the
> > > different signals).
> > 
> > So what I don't see this patch doing; and I don't remember if cpufreq is
> > ready for this at all, is set the util_dl as min/guaranteed freq and
> > util_cfs+util_dl as requested freq.
> 
> I'm totally unsure what you mean here.

I was thinking of the CPPC/HWP stuff, where you can set different
frequencies with different levels of guarantees.

We'd want to set util_dl as the minimum (guaranteed) performance, and
util_dl + util_cfs as the desired performance level.

> cpufreq doesn't have a "guaranteed frequency" concept of any sort right now.

I was afraid of that ;-) I think we want a comment in the code stating
that this is the desired goal though. Then once cpufreq is ready to deal
with it we can change it..