linux-kernel - Re: [PATCH v2 5/6] sched/dl: Optimize select_task_rq

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Date:	Tue, 04 Nov 2014 19:24:47 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	"pang.xunlei" <pang.xunlei@...aro.org>,
	linux-kernel@...r.kernel.org
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v2 5/6] sched/dl: Optimize select_task_rq_dl() for non-DL
 curr task


On 14/11/4 下午7:13, pang.xunlei wrote:
> When selecting the cpu for a waking DL task, if curr is a non-DL
> task which is bound only on this cpu, then we can give it a chance
> to select a different cpu for this DL task to avoid curr starving.
>
> Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
> ---
>   kernel/sched/deadline.c |   14 ++++++++++----
>   1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 7b0b2d2..1f64d4a 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -954,6 +954,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
>   	struct task_struct *curr;
>   	struct rq *rq;
>   
> +	if (p->nr_cpus_allowed == 1)
> +		goto out;
> +
>   	if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK)
>   		goto out;

I don't think you use right branch of tip tree.

Regards,
Wanpeng Li

>   
> @@ -970,11 +973,14 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
>   	 * can!) we prefer to send it somewhere else. On the
>   	 * other hand, if it has a shorter deadline, we
>   	 * try to make it stay here, it might be important.
> +	 *
> +	 * If the current task on @p's runqueue is a non-DL task,
> +	 * and this task is bound on current runqueue, then try to
> +	 * see if we can wake this DL task up on a different runqueue,
>   	 */
> -	if (unlikely(dl_task(curr)) &&
> -	    (curr->nr_cpus_allowed < 2 ||
> -	     !dl_entity_preempt(&p->dl, &curr->dl)) &&
> -	    (p->nr_cpus_allowed > 1)) {
> +	if (unlikely(curr->nr_cpus_allowed < 2) ||
> +		unlikely(dl_task(curr) &&
> +				!dl_entity_preempt(&p->dl, &curr->dl))) {
>   		int target = find_later_rq(p);
>   
>   		if (target != -1)

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