linux-kernel - Re: [PATCH v5] sched/deadline: remove useless param from setup_new_dl

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Date:	Fri, 5 Aug 2016 20:41:29 +0800
From:	Xunlei Pang <xpang@...hat.com>
To:	Juri Lelli <juri.lelli@....com>, peterz@...radead.org
Cc:	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, luca.abeni@...tn.it
Subject: Re: [PATCH v5] sched/deadline: remove useless param from
 setup_new_dl_entity

On 2016/08/05 at 18:09, Juri Lelli wrote:
> setup_new_dl_entity() takes two parameters, but it only actually uses
> one of them, under a different name, to setup a new dl_entity, after:
>
>  2f9f3fdc928 "sched/deadline: Remove dl_new from struct sched_dl_entity"
>
> as we currently do
>
>  setup_new_dl_entity(&p->dl, &p->dl)
>
> However, before Luca's change we were doing
>
>  setup_new_dl_entity(dl_se, pi_se)
>
> in update_dl_entity() for a dl_se->new entity: we were using pi_se's
> parameters (the potential PI donor) for setting up a new entity.
>
> This change removes the useless second parameter of setup_new_dl_entity().
> While we are at it we also optimize things further calling setup_new_dl_
> entity() only for already queued tasks, since (as pointed out by Xunlei)
> we already do the very same update at tasks wakeup time anyway. By doing
> so, we don't need to worry about a potential PI donor anymore, as rt_
> mutex_setprio() takes care of that already for us.
>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Luca Abeni <luca.abeni@...tn.it>
> Cc: Xunlei Pang <xpang@...hat.com>
> Signed-off-by: Juri Lelli <juri.lelli@....com>

Reviewed-by: Xunlei Pang <xlpang@...hat.com>


>
> ---
>  Changes from v4:
>    - remove dead code checking for boosted status, as never triggered
>      after rt_mutex_setprio()
>
>  Changes from v3:
>    - call setup_new_dl_entity only if task is enqueued already
>
>  Changes from v2:
>    - optimize by calling rt_mutex_get_top_task only if the task is
>      boosted (as suggested by Steve)
>
>  Changes from v1:
>    - Steve pointed out that we were actually using the second parameter
>      to permorm initialization
>    - Luca confirmed that behavior is slightly changed w.r.t. before his
>      change
>    - changelog updated and original behavior restored
> ---
>  kernel/sched/deadline.c | 35 ++++++++++++++++++++++-------------
>  1 file changed, 22 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index fcb7f0217ff4..9491dbe039e8 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -346,12 +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);
>  
> +	WARN_ON(dl_se->dl_boosted);
>  	WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
>  
>  	/*
> @@ -367,8 +367,8 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se,
>  	 * future; in fact, we must consider execution overheads (time
>  	 * spent on hardirq context, etc.).
>  	 */
> -	dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> -	dl_se->runtime = pi_se->dl_runtime;
> +	dl_se->deadline = rq_clock(rq) + dl_se->dl_deadline;
> +	dl_se->runtime = dl_se->dl_runtime;
>  }
>  
>  /*
> @@ -1720,19 +1720,28 @@ 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);
>  
> -	if (task_on_rq_queued(p) && rq->curr != p) {
> +	if (task_on_rq_queued(p)) {
> +		/*
> +		 * If p is not queued we will update its parameters at next
> +		 * wakeup. If p is dl_boosted we already updated its params in
> +		 * rt_mutex_setprio()->enqueue_task(..., ENQUEUE_REPLENISH),
> +		 * p's deadline being now already after rq_clock(rq).
> +		 */
> +		if (dl_time_before(p->dl.deadline, rq_clock(rq)))
> +			setup_new_dl_entity(&p->dl);
> +
> +		if (rq->curr != p) {
>  #ifdef CONFIG_SMP
> -		if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
> -			queue_push_tasks(rq);
> +			if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
> +				queue_push_tasks(rq);
>  #else
> -		if (dl_task(rq->curr))
> -			check_preempt_curr_dl(rq, p, 0);
> -		else
> -			resched_curr(rq);
> +			if (dl_task(rq->curr))
> +				check_preempt_curr_dl(rq, p, 0);
> +			else
> +				resched_curr(rq);
>  #endif
> +		}
>  	}
>  }
>