linux-kernel - Re: [tip: sched/core] sched/topology: Introduce sched

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Message-ID: <CAKfTPtDHuM99sy7eU1LQSAUuZNb6VNUr0uYq4B7Dy3WyQcavqQ@mail.gmail.com>
Date:   Wed, 24 May 2023 15:02:18 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Len Brown <len.brown@...el.com>, x86@...nel.org
Subject: Re: [tip: sched/core] sched/topology: Introduce sched_group::flags

On Tue, 23 May 2023 at 12:59, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Oct 05, 2021 at 02:12:02PM -0000, tip-bot2 for Ricardo Neri wrote:
>
> > index 4e8698e..c56faae 100644
> > --- a/kernel/sched/topology.c
> > +++ b/kernel/sched/topology.c
> > @@ -716,8 +716,20 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
> >               tmp = sd;
> >               sd = sd->parent;
> >               destroy_sched_domain(tmp);
> > -             if (sd)
> > +             if (sd) {
> > +                     struct sched_group *sg = sd->groups;
> > +
> > +                     /*
> > +                      * sched groups hold the flags of the child sched
> > +                      * domain for convenience. Clear such flags since
> > +                      * the child is being destroyed.
> > +                      */
> > +                     do {
> > +                             sg->flags = 0;
> > +                     } while (sg != sd->groups);
>
>
> I happened to be reading this here code and aren't we missing:
>
>         sg = sg->next;
>
> somewhere in that loop?

Yes, I missed that.

That being said, the only reason for sd to be degenerate is that there
is only 1 group. Otherwise we will keep it and degenerate parents
instead