linux-kernel - Re: [Patch v4 4/6] sched/fair: update cpu

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Message-ID: <CAKfTPtCQe8qd1e5s-jf_5C7eaGVc7OYcXYgdvBK+ACF8aL7ByQ@mail.gmail.com>
Date:   Thu, 31 Oct 2019 17:31:39 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Qais Yousef <qais.yousef@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Quentin Perret <qperret@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [Patch v4 4/6] sched/fair: update cpu_capcity to reflect thermal pressure

On Thu, 31 Oct 2019 at 17:17, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 31.10.19 16:48, Vincent Guittot wrote:
> > On Thu, 31 Oct 2019 at 16:38, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
> >>
> >> On 31.10.19 11:53, Qais Yousef wrote:
> >>> On 10/28/19 16:30, Peter Zijlstra wrote:
> >>>> On Wed, Oct 23, 2019 at 01:28:40PM +0100, Qais Yousef wrote:
> >>>>> On 10/22/19 16:34, Thara Gopinath wrote:
>
> [...]
>
> >>> To make sure I got this correctly - it's because avg_thermal.load_avg
> >>> represents delta_capacity which is already a 'converted' form of load. So this
> >>> makes avg_thermal.load_avg a util_avg really. Correct?
> >>>
> >>> If I managed to get it right somehow. It'd be nice if we can do inverse
> >>> conversion on delta_capacity so that avg_thermal.{load_avg, util_avg} meaning
> >>> is consistent across the board. But I don't feel strongly about it if this gets
> >>> documented properly.
> >>
> >> So why can't we use rq->avg_thermal.util_avg here? Since capacity is
> >> closer to util than to load?
> >>
> >> Is it because you want to use the influence of ___update_load_sum(...,
> >> unsigned long load eq. per-cpu delta_capacity in your signal?
> >>
> >> Why not call it this way then?
> >
> > util_avg tracks a binary state with 2 fixed weights: running(1024)  vs
> > not running (0)
> > In the case of thermal pressure, we want to track how much pressure is
> > put on the CPU: capping to half the max frequency is not the same as
> > capping only 10%
> > load_avg is not boolean but you set the weight  you want to apply and
> > this weight reflects the amount of pressure.
>
> I see. This is what I meant by 'load (weight) eq. per-cpu delta_capacity
> (pressure)'.
>
>
> >> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> >> index 38210691c615..d3035457483f 100644
> >> --- a/kernel/sched/pelt.c
> >> +++ b/kernel/sched/pelt.c
> >> @@ -357,9 +357,9 @@ int update_thermal_load_avg(u64 now, struct rq *rq,
> >> u64 capacity)
> >>  {
> >>         if (___update_load_sum(now, &rq->avg_thermal,
> >>                                capacity,
> >> -                              capacity,
> >> -                              capacity)) {
> >> -               ___update_load_avg(&rq->avg_thermal, 1, 1);
> >> +                              0,
> >> +                              0)) {
> >> +               ___update_load_avg(&rq->avg_thermal, 1, 0);
> >>                 return 1;
> >>         }
>
> So we could call it this way since we don't care about runnable_load or
> util?

one way or the other is quite similar but the current solution is
aligned with other irq, rt, dl signals which duplicates the same state
in each fields