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    SubjectRe: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure
    On Fri, 17 Jan 2020 at 15:55, Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > On Fri, Jan 17, 2020 at 02:22:51PM +0100, Vincent Guittot wrote:
    > > On Thu, 16 Jan 2020 at 16:15, Peter Zijlstra <peterz@infradead.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?

    No we should not. Weird artifacts happens when we
    add/subtract/propagate signals between each other and then apply pelt
    algorithm on the results. In the case of thermal signal, we only add
    it to others to update cpu_capacity but pelt algo is then not applied
    on it. The error because of some signals being at segment boundaries
    whereas others are not, is limited to 2% and doesn't accumulate over
    time.

    >
    > 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.

    TBH I was thinking of doing the opposite for update_irq_load_avg which
    hides the clock that is used for irq_avg. This helps to easily
    identify which signals use the exact same clock and can be mixed to
    create a new pelt signal and which can't

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