linux-kernel - Re: [PATCH v2 1/1] cgroup: make per-cgroup pressure stall tracking configurable

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Date:   Tue, 18 May 2021 11:55:59 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, macro@...am.me.uk,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        cgroups mailinglist <cgroups@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v2 1/1] cgroup: make per-cgroup pressure stall tracking configurable

On Tue, May 18, 2021 at 11:52 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, May 17, 2021 at 07:02:00PM -0700, Suren Baghdasaryan wrote:
>
> > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> > index cc25a3cff41f..4b8e72640ac9 100644
> > --- a/kernel/sched/psi.c
> > +++ b/kernel/sched/psi.c
> > @@ -148,6 +148,7 @@
> >  static int psi_bug __read_mostly;
> >
> >  DEFINE_STATIC_KEY_FALSE(psi_disabled);
> > +DEFINE_STATIC_KEY_FALSE(psi_cgroups_disabled);
>
> I'm thinking the whole thing will be easier/clearer when you make this:
>
> DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled);
>

Sounds good. Will respin another version. Thanks for reviewing!


> >
> >  #ifdef CONFIG_PSI_DEFAULT_DISABLED
> >  static bool psi_enable;
> > @@ -211,6 +212,9 @@ void __init psi_init(void)
> >               return;
> >       }
> >
> > +     if (!cgroup_psi_enabled())
> > +             static_branch_enable(&psi_cgroups_disabled);
>
>         if (!cgroup_psi_enabled())
>                 static_branch_disable(&psi_cgroups_enabled);
>
> > +
> >       psi_period = jiffies_to_nsecs(PSI_FREQ);
> >       group_init(&psi_system);
> >  }
> > @@ -744,23 +748,23 @@ static void psi_group_change(struct psi_group *group, int cpu,
> >
> >  static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
> >  {
> > +     if (*iter == &psi_system)
> > +             return NULL;
> > +
> >  #ifdef CONFIG_CGROUPS
> > +     if (!static_branch_likely(&psi_cgroups_disabled)) {
>
>         if (static_branch_likely(&psi_cgroups_enabled)) {
>
> > +             struct cgroup *cgroup = NULL;
> >
> > +             if (!*iter)
> > +                     cgroup = task->cgroups->dfl_cgrp;
> > +             else
> > +                     cgroup = cgroup_parent(*iter);
> >
> > +             if (cgroup && cgroup_parent(cgroup)) {
> > +                     *iter = cgroup;
> > +                     return cgroup_psi(cgroup);
> > +             }
> >       }
> >  #endif
> >       *iter = &psi_system;
> >       return &psi_system;
>
> But yes, very nice.
>
> --
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>