linux-kernel - Re: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure

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Date:   Fri, 17 Jan 2020 15:55:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Thara Gopinath <thara.gopinath@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Zhang Rui <rui.zhang@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        viresh kumar <viresh.kumar@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Amit Kucheria <amit.kucheria@...durent.com>
Subject: Re: [Patch v8 4/7] sched/fair: Enable periodic update of average
 thermal pressure

On Fri, Jan 17, 2020 at 02:22:51PM +0100, Vincent Guittot wrote:
> On Thu, 16 Jan 2020 at 16:15, Peter Zijlstra <peterz@...radead.org> wrote:

> >
> > That there indentation trainwreck is a reason to rename the function.
> >
> >         decayed = update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
> >                   update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
> >                   update_thermal_load_avg(rq_clock_task(rq), rq, thermal_pressure) |
> >                   update_irq_load_avg(rq, 0);
> >
> > Is much better.
> >
> > But now that you made me look at that, I noticed it's using a different
> > clock -- it is _NOT_ using now/rq_clock_pelt(), which means it'll not be
> > in sync with the other averages.
> >
> > Is there a good reason for that?
> 
> We don't need to apply frequency and cpu capacity invariance on the
> thermal capping signal which is  what rq_clock_pelt does

Hmm, I suppose that is true, and that really could've done with a
comment. Now clock_pelt is sort-of in sync with clock_task, but won't it
still give weird artifacts by having it on a slightly different basis?

Anyway, looking at this, would it make sense to remove the @now argument
from update_*_load_avg()? All those functions already take @rq, and
rq_clock_*() are fairly trivial inlines.