linux-kernel - Re: [PATCH v2 2/3] sched/dl: Cleanup prio_changed

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Message-ID: <544688A1.7010403@arm.com>
Date:	Tue, 21 Oct 2014 17:24:01 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Kirill Tkhai <ktkhai@...allels.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Kirill Tkhai <tkhai@...dex.ru>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 2/3] sched/dl: Cleanup prio_changed_dl()

Hi Kirill,

On 02/10/14 10:52, Kirill Tkhai wrote:
> В Чт, 02/10/2014 в 11:36 +0200, Peter Zijlstra пишет:
>> On Wed, Oct 01, 2014 at 01:04:35AM +0400, Kirill Tkhai wrote:
>>> From: Kirill Tkhai <ktkhai@...allels.com>
>>>
>>> rq->curr task can't be in "dequeued" state in prio_changed_dl().
>>> (The only place we can have that is __schedule()). So, we delete
>>> rq->curr check.
>>
>> the CBS timer can throttle it right?
> 
> Yeah, it's better to check for on_dl_rq():
> 
> [PATCH]sched/dl: Cleanup prio_changed_dl()
>     
> rq->curr task can't be in "dequeued" state in prio_changed_dl().
> (The only place we can have that is __schedule()). So, we delete
> rq->curr check.
> 
> We shouldn't do balancing if deadline task is throttled too.
> 
> Also delete "else" branch which is dead code (switched_to_dl()
> is not interested in dequeued tasks and we are not interested
> in balancing in this case).
> 

So, I agree that calling switched_to_dl() makes little sense,
but don't we have to deal with updates to not running tasks as
in rt.c? Something like this maybe?

>From 75ee75a5fd76526baaed3ba8a58f3ff7daa89cd6 Mon Sep 17 00:00:00 2001
From: Juri Lelli <juri.lelli@....com>
Date: Tue, 21 Oct 2014 17:15:15 +0100
Subject: [PATCH] sched/deadline: cleanup prio_changed_dl()

---
 kernel/sched/deadline.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 28d6088..1e62e31 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1661,7 +1661,10 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 static void prio_changed_dl(struct rq *rq, struct task_struct *p,
 			    int oldprio)
 {
-	if (task_on_rq_queued(p) || rq->curr == p) {
+	if (!on_dl_rq(&p->dl))
+		return;
+
+	if (rq->curr == p) {
 #ifdef CONFIG_SMP
 		/*
 		 * This might be too much, but unfortunately
@@ -1688,8 +1691,15 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
 		 */
 		resched_curr(rq);
 #endif /* CONFIG_SMP */
-	} else
-		switched_to_dl(rq, p);
+	} else {
+		/*
+		 * This task is not running, so if its deadline is
+		 * now more imminent than that of the current running
+		 * task then reschedule.
+		 */
+		if (dl_time_before(p->dl.deadline, rq->curr->dl.deadline))
+			resched_curr(rq);
+	}
 }
 
 const struct sched_class dl_sched_class = {
-- 
2.1.0

Thanks,

- Juri

> Signed-off-by: Kirill Tkhai <ktkhai@...allels.com>
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 63f8b4a..ccea917 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1638,35 +1638,33 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
>  static void prio_changed_dl(struct rq *rq, struct task_struct *p,
>  			    int oldprio)
>  {
> -	if (task_on_rq_queued(p) || rq->curr == p) {
> +	if (!on_dl_rq(&p->dl))
> +		return;
>  #ifdef CONFIG_SMP
> -		/*
> -		 * This might be too much, but unfortunately
> -		 * we don't have the old deadline value, and
> -		 * we can't argue if the task is increasing
> -		 * or lowering its prio, so...
> -		 */
> -		if (!rq->dl.overloaded)
> -			pull_dl_task(rq);
> -
> -		/*
> -		 * If we now have a earlier deadline task than p,
> -		 * then reschedule, provided p is still on this
> -		 * runqueue.
> -		 */
> -		if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
> -		    rq->curr == p)
> -			resched_curr(rq);
> -#else
> -		/*
> -		 * Again, we don't know if p has a earlier
> -		 * or later deadline, so let's blindly set a
> -		 * (maybe not needed) rescheduling point.
> -		 */
> +	/*
> +	 * This might be too much, but unfortunately
> +	 * we don't have the old deadline value, and
> +	 * we can't argue if the task is increasing
> +	 * or lowering its prio, so...
> +	 */
> +	if (!rq->dl.overloaded)
> +		pull_dl_task(rq);
> +	/*
> +	 * If we now have a earlier deadline task than p,
> +	 * then reschedule, provided p is still on this
> +	 * runqueue.
> +	 */
> +	if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
> +	    rq->curr == p)
>  		resched_curr(rq);
> +#else
> +	/*
> +	 * Again, we don't know if p has a earlier
> +	 * or later deadline, so let's blindly set a
> +	 * (maybe not needed) rescheduling point.
> +	 */
> +	resched_curr(rq);
>  #endif /* CONFIG_SMP */
> -	} else
> -		switched_to_dl(rq, p);
>  }
>  
>  const struct sched_class dl_sched_class = {
> 
> 
> 

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