linux-kernel - Re: [PATCH] Prevent immediate process rescheduling

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Message-ID: <20090918195455.GC11726@elte.hu>
Date:	Fri, 18 Sep 2009 21:54:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mark Langsdorf <mark.langsdorf@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Prevent immediate process rescheduling


(fixed the Cc: lines)

* Mark Langsdorf <mark.langsdorf@....com> wrote:

> Prevent the scheduler from immediately rescheduling a process
> that just yielded if there is another process available.
> 
> Originally suggested by Mike Galbraith (efault@....de).
> 
> Signed-off-by: Mark Langsdorf <mark.langsdorf@....com>
> ---
>  kernel/sched_fair.c |   16 +++++++++++++++-
>  1 files changed, 15 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 652e8bd..4fad08f 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -353,11 +353,25 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
>  {
>  	struct rb_node *left = cfs_rq->rb_leftmost;
> +	struct sched_entity *se, *curr;
>  
>  	if (!left)
>  		return NULL;
>  
> -	return rb_entry(left, struct sched_entity, run_node);
> +	se = rb_entry(left, struct sched_entity, run_node);
> +	curr = &current->se;
> +
> +	/* 
> +	 * Don't select the entity who just tried to schedule away
> +	 * if there's another entity available.
> +	 */
> +	if (unlikely(se == curr && cfs_rq->nr_running > 1)) {
> +		struct rb_node *next_node = rb_next(&curr->run_node);
> +		if (next_node)
> +			se = rb_entry(next_node, struct sched_entity, run_node);
> +	}
> +
> +	return se;
>  }

I suspect some real workload is the motivation of this - what is that 
workload?

	Ingo
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