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

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Date:	Tue, 5 Jul 2016 10:20:13 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Juri Lelli <juri.lelli@....com>
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 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.

-- 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