linux-kernel - Re: [PATCH 1/6] sched/rt: check if curr can be pushed/pulled somewhere else in advance

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Date:	Thu, 30 Oct 2014 06:57:21 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org,
	Kirill Tkhai <tkhai@...dex.ru>,
	Kirill Tkhai <ktkhai@...allels.com>
Subject: Re: [PATCH 1/6] sched/rt: check if curr can be pushed/pulled somewhere
 else in advance

Cc Kirill,
2014/10/27 9:41, Wanpeng Li:
> This patch checks if current can be pushed/pulled somewhere else
> in advance to make logic clear.
>
> - If current can't be migrated, useless to reschedule, let's hope
>    task can move out.
> - If task is migratable, so let's not schedule it and see if it
>    can be pushed or pulled somewhere else.
>
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>   kernel/sched/rt.c | 14 ++++++++++----
>   1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 87ea5bf..ca1b7c7 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1351,16 +1351,22 @@ out:
>   
>   static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
>   {
> -	if (rq->curr->nr_cpus_allowed == 1)
> +	/*
> +	 * Current can't be migrated, useless to reschedule,
> +	 * let's hope p can move out.
> +	 */
> +	if (rq->curr->nr_cpus_allowed == 1 ||
> +		!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
>   		return;
>   
> +	/*
> +	 * p is migratable, so let's not schedule it and
> +	 * see if it is pushed or pulled somewhere else.
> +	 */
>   	if (p->nr_cpus_allowed != 1
>   	    && cpupri_find(&rq->rd->cpupri, p, NULL))
>   		return;
>   
> -	if (!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
> -		return;
> -
>   	/*
>   	 * There appears to be other cpus that can accept
>   	 * current and none to run 'p', so lets reschedule

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