linux-kernel - Re: [PATCH RESEND v2] sched/deadline: do not try to push tasks if pinned task switches to dl

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Message-ID: <5446316B.4070707@arm.com>
Date:	Tue, 21 Oct 2014 11:11:55 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Kirill V Tkhai <tkhai@...dex.ru>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND v2] sched/deadline: do not try to push tasks if
 pinned task switches to dl

Hi,

On 11/10/14 01:58, Wanpeng Li wrote:
> As Kirill mentioned(https://lkml.org/lkml/2013/1/29/118):
> | If rq has already had 2 or more pushable tasks and we try to add a 
> | pinned task then call of push_rt_task will just waste a time.
> 
> Just switched pinned task is not able to be pushed. If the rq had had
                                                                 ^
                                                                has
> several dl tasks before they have already been considered as candidates
> to be pushed (or pulled). This patch done the same behavior as rt class
                                        ^
                                    implements? aligns to...

> which introduced by commit 10447917551e ("sched/rt: Do not try to push 
> tasks if pinned task switches to RT").
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
> v1 -> v2:
>  * use 12 or more chars for the git commit ID
> 
>  kernel/sched/deadline.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index abfaf3d..cf7c9b6 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1603,7 +1603,8 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
>  
>  	if (task_on_rq_queued(p) && rq->curr != p) {
>  #ifdef CONFIG_SMP
> -		if (rq->dl.overloaded && push_dl_task(rq) && rq != task_rq(p))
> +		if (p->nr_cpus_allowed > 1 && rq->dl.overloaded
> +				&& push_dl_task(rq) && rq != task_rq(p))

I'd personally align this && to p->nr_cpus_allowed, but that's just my
personal taste, though. :)

>  			/* Only reschedule if pushing failed */
>  			check_resched = 0;
>  #endif /* CONFIG_SMP */
> 

Anyway, the change looks good, thanks!

Best,

- Juri

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