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

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Message-ID: <Zp_BYrWoGADj5gwa@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 23 Jul 2024 16:42:42 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Wander Lairson Costa <wander@...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 23/07/24 09:27, Wander Lairson Costa wrote:
> 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.

Think we can drop it yes.

Thanks,
Juri