Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210513175349.959661-1-surenb@google.com> <YJ5iAvqAmIhzJRot@hirez.programming.kicks-ass.net>
In-Reply-To: <YJ5iAvqAmIhzJRot@hirez.programming.kicks-ass.net>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Fri, 14 May 2021 08:54:47 -0700
Message-ID: <CAJuCfpHy+MknCepfjx9XYUA1j42Auauv7MFQbt+zOU-tA4gasA@mail.gmail.com>
Subject: Re: [PATCH 1/1] cgroup: make per-cgroup pressure stall tracking configurable
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>,
        lizefan.x@bytedance.com, Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Benjamin Segall <bsegall@google.com>, mgorman@suse.de,
        Minchan Kim <minchan@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>, bristot@redhat.com,
        "Paul E . McKenney" <paulmck@kernel.org>, rdunlap@infradead.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, macro@orcam.me.uk,
        Viresh Kumar <viresh.kumar@linaro.org>,
        mike.kravetz@oracle.com, linux-doc@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        cgroups mailinglist <cgroups@vger.kernel.org>,
        kernel-team <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, May 14, 2021 at 4:42 AM Peter Zijlstra <peterz@infradead.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!

>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
>