linux-kernel - Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

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Date:   Fri, 22 Jun 2018 14:14:30 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        viresh kumar <viresh.kumar@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Quentin Perret <quentin.perret@....com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

On Fri, 22 Jun 2018 at 13:41, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Jun 22, 2018 at 10:10:32AM +0200, Vincent Guittot wrote:
> > On Thu, 21 Jun 2018 at 20:57, Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > > So this (and the dl etc. equivalents) result in exactly the problems
> > > > complained about last time, no?
> > > >
> > > > What I proposed was something along the lines of:
> > > >
> > > >       util = 1024 * sg_cpu->util_cfs;
> > > >       util /= (1024 - (sg_cpu->util_rt + sg_cpu->util_dl + ...));
> > > >
> > > >       return min(sg_cpu->max, util + sg_cpu->bw_dl);
> >
> > I see that you use sg_cpu->util_dl and sg_cpu->bw_dl in your equation
> > above but this patch 04 only adds rt util_avg and the dl util_avg has
> > not been added yet.
> >  dl util_avg is added in patch 6
> > So for this patch, we are only using sg_cpu->bw_dl
>
> Yeah, not the point really.
>
> It is about how we're going to use the (rt,dl,irq etc..) util values,
> more than which particular one was introduced here.

ok

>
> I'm just not a big fan of the whole: freq := cfs_util + rt_util thing
> (as would be obvious by now).

so I'm not sure to catch what you don't like with the sum ? Is it the
special case for dl and how we switch between dl_bw and dl util_avg
which can generate a drop in frequency
Because the increase is linear regarding rt and cfs