linux-kernel - Re: [patch] DLS: fix switched_from

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Date:	Sun, 22 Apr 2012 18:10:53 +0200
From:	Juri Lelli <juri.lelli@...il.com>
To:	Hillf Danton <dhillf@...il.com>
CC:	Dario Faggioli <raistlin@...ux.it>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] DLS: fix switched_from_dl

On 04/10/2012 04:25 PM, Hillf Danton wrote:
> Pull only if the current task switches from DLS, since it was not preempted
> by pushable tasks waiting on other runqueues.
>
> Signed-off-by: Hillf Danton<dhillf@...il.com>
> ---
>
> --- a/kernel/sched_dl.c	Mon Apr  9 19:39:56 2012
> +++ b/kernel/sched_dl.c	Tue Apr 10 21:23:52 2012
> @@ -1466,12 +1466,7 @@ static void switched_from_dl(struct rq *
>   		hrtimer_try_to_cancel(&p->dl.dl_timer);
>
>   #ifdef CONFIG_SMP
> -	/*
> -	 * Since this might be the only -deadline task on the rq,
> -	 * this is the right place to try to pull some other one
> -	 * from an overloaded cpu, if any.
> -	 */
> -	if (!rq->dl.dl_nr_running)
> +	if (p == rq->curr)
>   		pull_dl_task(rq);
>   #endif
>   }
> --

I'd stay with the original code. p (former -dl task) is going away
(changed its scheduling class from -dl to something else). If it was
the last -dl task on rq I'd probably want to pull someone else. No
assumptions needed in this case.

Thanks,

- Juri
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