linux-kernel - Re: [PATCH 2/3] sched/deadline: avoid redundant check for boosted task

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Message-ID: <CAAq0SU=s+UMZWXBfHWG4tPCM5VM35T6B0i+JcimbRXm0Q+ZvJA@mail.gmail.com>
Date: Tue, 23 Jul 2024 09:27:40 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Juri Lelli <juri.lelli@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
	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>, 
	Valentin Schneider <vschneid@...hat.com>, "open list:SCHEDULER" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] sched/deadline: avoid redundant check for boosted task

On Tue, Jul 23, 2024 at 5:55 AM Juri Lelli <juri.lelli@...hat.com> wrote:
>
> Hi Wander,
>
> On 22/07/24 10:29, Wander Lairson Costa wrote:
> > enqueue_dl_entity only calls setup_new_dl_entity if the task is not
> > boosted, so the WARN_ON check is unnecessary.
> >
> > Signed-off-by: Wander Lairson Costa <wander@...hat.com>
> > ---
> >  kernel/sched/deadline.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index 312e8fa7ce94..908d5ce79425 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -785,12 +785,11 @@ static inline void replenish_dl_new_period(struct sched_dl_entity *dl_se,
> >   * one, and to (try to!) reconcile itself with its own scheduling
> >   * parameters.
> >   */
> > -static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
> > +static inline void __setup_new_dl_entity(struct sched_dl_entity *dl_se)
> >  {
> >       struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> >       struct rq *rq = rq_of_dl_rq(dl_rq);
> >
> > -     WARN_ON(is_dl_boosted(dl_se));
> >       WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
> >
> >       /*
> > @@ -809,6 +808,12 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
> >       replenish_dl_new_period(dl_se, rq);
> >  }
> >
> > +static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
> > +{
> > +     WARN_ON(is_dl_boosted(dl_se));
> > +     __setup_new_dl_entity(dl_se);
> > +}
> > +
>
> So, the other call path is from dl_server_start() and for this we know
> the entity is not boosted either. We could probably just remove the
> WARN_ON w/o the additional wrapper function. That said, considering it's
> not fast path, I wonder if we actually want to leave the WARN_ON where
> it is, so that we can catch potential future erroneous usages?
>

Yeah, if you feel the patch is not worth it, I am more in favor of
dropping the patch than removing the WARN_ON.

> Thanks,
> Juri
>