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

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Date:	Wed, 6 Jul 2016 10:46:28 +0200
From:	luca abeni <luca.abeni@...tn.it>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Juri Lelli <juri.lelli@....com>, peterz@...radead.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com
Subject: Re: [PATCH v2] sched/deadline: remove useless param from
 setup_new_dl_entity

On Tue, 5 Jul 2016 10:20:13 -0400
Steven Rostedt <rostedt@...dmis.org> 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 &&
> 	    (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.

If something like this is done, I think that enqueue_task_dl() (that
contains similar code) should be updated too.


			Thanks,
				Luca

> 
> -- Steve
> 
> 
> > +	/*
> >  	 * We use the regular wall clock time to set deadlines in
> > the
> >  	 * future; in fact, we must consider execution overheads
> > (time
> >  	 * spent on hardirq context, etc.).
> > @@ -1721,7 +1729,7 @@ static void switched_from_dl(struct rq *rq,
> > struct task_struct *p) static void switched_to_dl(struct rq *rq,
> > struct task_struct *p) {
> >  	if (dl_time_before(p->dl.deadline, rq_clock(rq)))
> > -		setup_new_dl_entity(&p->dl, &p->dl);
> > +		setup_new_dl_entity(&p->dl);
> >  
> >  	if (task_on_rq_queued(p) && rq->curr != p) {
> >  #ifdef CONFIG_SMP  
>