linux-kernel - Re: [RFC PATCH V3 4/6] sched/deadline: Introduce deadline servers

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Date:   Tue, 4 Jul 2023 13:28:10 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     Valentin Schneider <vschneid@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vineeth Pillai <vineeth@...byteword.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [RFC PATCH V3 4/6] sched/deadline: Introduce deadline servers

On Tue, Jul 4, 2023 at 1:25 PM Joel Fernandes <joel@...lfernandes.org> wrote:
>
> On Tue, Jul 4, 2023 at 11:52 AM Daniel Bristot de Oliveira
> <bristot@...hat.com> wrote:
> >
> >
> > Back from EOSS...
> >
> > On 6/23/23 18:47, Valentin Schneider wrote:
> > > On 08/06/23 17:58, Daniel Bristot de Oliveira wrote:
> > >> @@ -2033,9 +2147,20 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
> > >>      struct task_struct *p;
> > >>
> > >>      p = pick_task_dl(rq);
> > >> -    if (p)
> > >> +    if (!p)
> > >> +            return p;
> > >> +
> > >> +    /*
> > >> +     * XXX: re-check !dl_server, changed from v2 because of
> > >> +     * pick_next_task_dl change
> > >> +     */
> > >> +    if (!dl_server(&p->dl))
> > >>              set_next_task_dl(rq, p, true);
> > >>
> > >
> > > Should this be
> > >
> > >        if (!p->server)
> > >
> > > instead? AFAICT dl_server(&p->dl) can never be true since there's no
> > > pi_se-like link to the server via the dl_se, only via the task_struct, and
> > > the server pick cannot return the server itself (as it's a pure sched_entity).
> >
> > makes sense... I will check that in the v4.
>
> Makes sense to me too. Since p is either a real DL task or a CFS task,
> "if (dl_server(&p->dl))" is incorrect.  "if (p->server)" is the right
> check.

Grr, "if (!p->server)" I mean. Which ensures that set_next_task_dl()
is not called on a non-DL task.

 - Joel