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

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Date:   Fri, 22 Jun 2018 10:10:32 +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 Thu, 21 Jun 2018 at 20:57, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Jun 21, 2018 at 08:45:24PM +0200, Peter Zijlstra wrote:
> > On Fri, Jun 08, 2018 at 02:09:47PM +0200, Vincent Guittot wrote:
> > >  static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
> > >  {
> > >     struct rq *rq = cpu_rq(sg_cpu->cpu);
> > > +   unsigned long util;
> > >
> > >     if (rq->rt.rt_nr_running)
> > >             return sg_cpu->max;
> > >
> > > +   util = sg_cpu->util_dl;
> > > +   util += sg_cpu->util_cfs;
> > > +   util += sg_cpu->util_rt;
> > > +
> > >     /*
> > >      * Utilization required by DEADLINE must always be granted while, for
> > >      * FAIR, we use blocked utilization of IDLE CPUs as a mechanism to
> > > @@ -197,7 +204,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
> > >      * util_cfs + util_dl as requested freq. However, cpufreq is not yet
> > >      * ready for such an interface. So, we only do the latter for now.
> > >      */
> > > -   return min(sg_cpu->max, (sg_cpu->util_dl + sg_cpu->util_cfs));
> > > +   return min(sg_cpu->max, util);
> > >  }
> >
> > 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

> >
> > Where we, instead of directly adding the various util signals.
>
> That looks unfinished; I think that wants to include: "we renormalize
> the CFS signal".
>
> > I now see an email from Quentin asking if these things are not in fact
> > the same, but no, they are not. The difference is that the above only
> > affects the CFS signal and will re-normalize the utilization of an
> > 'always' running task back to 1 by compensating for the stolen capacity.
> >
> > But it will not, like these here patches, affect the OPP selection of
> > other classes. If there is no CFS utilization (or very little), then the
> > renormalization will not matter, and the existing DL bandwidth
> > compuation will be unaffected.
> >