linux-kernel - Re: [PATCH v5 7/7] sched/fair: Add latency list

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Date:   Wed, 26 Oct 2022 15:55:34 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Youssef Esmat <youssefesmat@...omium.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org,
        parth@...ux.ibm.com, qais.yousef@....com, chris.hyser@...cle.com,
        valentin.schneider@....com, patrick.bellasi@...bug.net,
        David.Laight@...lab.com, pjt@...gle.com, pavel@....cz,
        tj@...nel.org, qperret@...gle.com, tim.c.chen@...ux.intel.com,
        joshdon@...gle.com, timj@....org, joel@...lfernandes.org
Subject: Re: [PATCH v5 7/7] sched/fair: Add latency list

On Wed, 26 Oct 2022 at 12:44, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 12/10/2022 17:21, Vincent Guittot wrote:
> > Le mardi 11 oct. 2022 ï¿½ 18:54:27 (-0500), Youssef Esmat a ï¿½crit :
> >> Hi Vincent,
> >>
> >> On Tue, Oct 11, 2022 at 12:10 PM Vincent Guittot
> >> <vincent.guittot@...aro.org> wrote:
>
> [...]
>
> > @@ -10894,12 +10898,17 @@ static int cpu_idle_write_s64(struct cgroup_subsys_state *css,
> >  static s64 cpu_latency_nice_read_s64(struct cgroup_subsys_state *css,
> >                                   struct cftype *cft)
> >  {
> > +     unsigned long period = sysctl_sched_latency;
> >       int last_delta = INT_MAX;
> >       int prio, delta;
> >       s64 weight;
> >
> > +     if (sched_feat(GENTLE_FAIR_SLEEPERS))
> > +             period >>= 1;
> > +
> >       weight = css_tg(css)->latency_offset * NICE_LATENCY_WEIGHT_MAX;
> > -     weight = div_s64(weight, sysctl_sched_latency);
> > +     period = sysctl_sched_latency;
>
> Looks like this line is wrong here, period has been set already for
> GENTLE_FAIR_SLEEPERS and !GENTLE_FAIR_SLEEPERS?

Yes, I have factorized this in a function and the new version that I'm
preparing so The formula is not duplicated with the risk of error like
above

>
> > +     weight = div_s64(weight, period);
> >
> >       /* Find the closest nice value to the current weight */
> >       for (prio = 0; prio < ARRAY_SIZE(sched_latency_to_weight); prio++) {
>
> [...]
>