linux-kernel - Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates

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Message-ID: <20171222121954.x3vgj7s6infdox46@hirez.programming.kicks-ass.net>
Date:   Fri, 22 Dec 2017 13:19:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates

On Fri, Dec 22, 2017 at 12:07:37PM +0000, Patrick Bellasi wrote:
> > I was thinking that since dl is a 'global' scheduler the reservation
> > would be too and thus the freq just needs a single CPU to be observed;
> 
> AFAIU global is only the admission control (which is something worth a
> thread by itself...) while the dl_se->dl_bw are aggregated into the
> dl_rq->running_bw, which ultimately represents the DL bandwidth
> required for just a CPU.

Oh urgh yes, forgot that.. then the dl freq stuff isn't strictly correct
I think. But yes, that's another thread.

> > but I suppose there's nothing stopping anybody from splitting a clock
> > domain down the middle scheduling wise. So yes, good point.
> 
> That makes sense... moreover, using the global utilization, we would
> end up asking for capacities which cannot be provided by a single CPU.

Yes, but that _should_ not be a problem if you clock them all high
enough. But this gets to be complicated real fast I think.

> > Blergh that'd make a mess of things again.
> 
> Actually, looking better at your patch: are we not just ok with that?
> 
> I mean, we don't need this check on idle_cpu since in
> sugov_aggregate_util we already skip the util=sg_cpu->max in case of
> !rq->rt.rt_nr_running, while we aggregate just CFS and DL requests.

Right, well, I don't actually have an environment to test this sanely,
so someone will have to go play with the various variations and see what
works.