linux-kernel - Re: [PATCH v2] sched/deadline: remove useless param from setup_new_dl

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Date:	Tue, 5 Jul 2016 15:39:33 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	peterz@...radead.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, luca.abeni@...tn.it
Subject: Re: [PATCH v2] sched/deadline: remove useless param from
 setup_new_dl_entity

On 05/07/16 10:20, Steven Rostedt wrote:
> On Wed, 29 Jun 2016 20:07:43 +0100
> Juri Lelli <juri.lelli@....com> wrote:
> 
> 
> > ---
> >  kernel/sched/deadline.c | 14 +++++++++++---
> >  1 file changed, 11 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index fcb7f0217ff4..2000ad2294d5 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -346,11 +346,12 @@ static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
> >   * 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,
> > -				       struct sched_dl_entity *pi_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);
> > +	struct task_struct *pi_task = rt_mutex_get_top_task(dl_task_of(dl_se));
> > +	struct sched_dl_entity *pi_se = dl_se;
> >  
> >  	WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
> >  
> > @@ -363,6 +364,13 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se,
> >  		return;
> >  
> >  	/*
> > +	 * Use the scheduling parameters of the top pi-waiter task,
> > +	 * if we have one from which we can inherit a deadline.
> > +	 */
> > +	if (pi_task && dl_se->dl_boosted && dl_prio(pi_task->normal_prio))
> > +		pi_se = &pi_task->dl;
> > +
> 
> OK, I'm micro-optimizing now, but hey, isn't this a fast path?
> 
> What about changing the above to:
> 
> 	struct task_struct *pi_task;
> 	[...]
> 
> 	if (dl_se->dl_boosted && dl_prio(pi_task->normal_prio &&
                                    ^
OK, we need to reorder these two
                                    V
> 	    (pi_task = rt_mutex_get_top_task(dl_task_of(dl_se)))
> 		pe_se = &pi_task->dl;
> 
> This way we don't need to do any work of looking at
> rt_mutex_get_top_task() for the normal case.
> 

But, yes. Looks good to me. I'll shoot a v3 ASAP.

Thanks,

- Juri