linux-kernel - Re: [PATCH 4/7] sched/deadline: reschedule if stop task slip in after pull operations

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Message-ID: <5534D48A.20304@arm.com>
Date:	Mon, 20 Apr 2015 11:27:22 +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:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] sched/deadline: reschedule if stop task slip in after
 pull operations

Hi,

On 06/04/2015 09:53, Wanpeng Li wrote:
> pull_dl_task can drop (and re-acquire) rq->lock, this means a stop task 
> can slip in, in which case we need to reschedule. This patch add the 
> reschedule when the scenario occurs.
> 

Ok, I guess it can happen. Doesn't RT have the same problem? It seems that
it also has to deal with DL tasks slipping in, right?

Thanks,

- Juri

> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  kernel/sched/deadline.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index b8b9355..844da0f 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1739,7 +1739,13 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
>  	if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
>  		return;
>  
> -	if (pull_dl_task(rq))
> +	/*
> +	 * pull_dl_task() can drop (and re-acquire) rq->lock; this
> +	 * means a stop task can slip in, in which case we need to
> +	 * reschedule.
> +	 */
> +	if (pull_dl_task(rq) ||
> +		(rq->stop && task_on_rq_queued(rq->stop)))
>  		resched_curr(rq);
>  }
>  
> @@ -1786,6 +1792,14 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
>  			pull_dl_task(rq);
>  
>  		/*
> +		 * pull_dl_task() can drop (and re-acquire) rq->lock; this
> +		 * means a stop task can slip in, in which case we need to
> +		 * reschedule.
> +		 */
> +		if (rq->stop && task_on_rq_queued(rq->stop))
> +			resched_curr(rq);
> +
> +		/*
>  		 * If we now have a earlier deadline task than p,
>  		 * then reschedule, provided p is still on this
>  		 * runqueue.
> 

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