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

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Date:   Fri, 14 May 2021 08:54:47 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
        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>, mgorman@...e.de,
        Minchan Kim <minchan@...nel.org>,
        Jonathan Corbet <corbet@....net>, bristot@...hat.com,
        "Paul E . McKenney" <paulmck@...nel.org>, 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@...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 1/1] cgroup: make per-cgroup pressure stall tracking configurable

On Fri, May 14, 2021 at 4:42 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, May 13, 2021 at 10:53:49AM -0700, Suren Baghdasaryan wrote:
>
> > +bool cgroup_psi_enabled(void)
> > +{
> > +     return (cgroup_feature_disable_mask & (1 << OPT_FEATURE_PRESSURE)) == 0;
> > +}
>
> > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> > index cc25a3cff41f..c73efd7d4fba 100644
> > --- a/kernel/sched/psi.c
> > +++ b/kernel/sched/psi.c
> > @@ -747,9 +747,12 @@ static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
> >  #ifdef CONFIG_CGROUPS
> >       struct cgroup *cgroup = NULL;
> >
> > -     if (!*iter)
> > +     if (!*iter) {
> > +             /* Skip to psi_system if per-cgroup accounting is disabled */
> > +             if (!cgroup_psi_enabled())
> > +                     goto update_sys;
> >               cgroup = task->cgroups->dfl_cgrp;
> > -     else if (*iter == &psi_system)
> > +     } else if (*iter == &psi_system)
> >               return NULL;
> >       else
> >               cgroup = cgroup_parent(*iter);
> > @@ -758,6 +761,7 @@ static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
> >               *iter = cgroup;
> >               return cgroup_psi(cgroup);
> >       }
> > +update_sys:
> >  #else
> >       if (*iter)
> >               return NULL;
>
> I'm confused; shouldn't that do the same as that #else branch?

Correct, for this function CONFIG_CGROUPS=n and
cgroup_disable=pressure are treated the same. True, from the code it's
not very obvious. Do you have some refactoring in mind that would make
it more explicit?

>Also, can you pretty please make cgroup_psi_enabled() a static_key ?

Certainly, will post an update on Monday.
Thanks for the feedback, Peter!

>
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