linux-kernel - Re: [Patch RT] Fix CFS load balancing for RT tasks

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Date:	Wed, 11 Jul 2007 19:06:20 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Sébastien Dugué <sebastien.dugue@...l.net>
Cc:	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux RT Users <linux-rt-users@...r.kernel.org>,
	Darren Hart <dvhltc@...ibm.com>,
	john stultz <johnstul@...ibm.com>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>,
	Gilles Carry <Gilles.Carry@....bull.net>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [Patch RT] Fix CFS load balancing for RT tasks

On Wed, 2007-07-11 at 16:47 +0200, Sébastien Dugué wrote:
>   The following patch fixes this by re-enabling the RT overload detection
> for the CFS. It may not be the right solution, maybe it should be incorporated
> into the other load balancing mechanisms. I did not digg deep enough yet
> to make that call ;-)
> 
>   P.S. Thanks to Steven Rostedt for logdev which is proving invaluable in
>        cases like this.
> 
>   Sébastien.

Nice catch. That was dropped during the CFS -> -rt merge.

	tglx

> ------------------
> 
>   The RT overload mechanism of the O(1) scheduler has not been activated
> in the new CFS.
> 
>   This patch fixes that by inserting calls to inc_rt_tasks() and dec_rt_tasks()
> in enqueue_task_rt() and dequeue_task_rt() respectively, which enables the
> balance_rt_tasks() to be run in the rt_overload case.
> 
> 
> Signed-off-by: Sébastien Dugué <sebastien.dugue@...l.net>
> 
> ---
>  kernel/sched_rt.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> Index: linux-2.6.21.5-rt20/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.21.5-rt20.orig/kernel/sched_rt.c	2007-07-11 10:46:26.000000000 +0200
> +++ linux-2.6.21.5-rt20/kernel/sched_rt.c	2007-07-11 10:46:50.000000000 +0200
> @@ -32,6 +32,8 @@ enqueue_task_rt(struct rq *rq, struct ta
>  
>  	list_add_tail(&p->run_list, array->queue + p->prio);
>  	__set_bit(p->prio, array->bitmap);
> +
> +	inc_rt_tasks(p, rq);
>  }
>  
>  /*
> @@ -44,6 +46,8 @@ dequeue_task_rt(struct rq *rq, struct ta
>  
>  	update_curr_rt(rq, now);
>  
> +	dec_rt_tasks(p, rq);
> +
>  	list_del(&p->run_list);
>  	if (list_empty(array->queue + p->prio))
>  		__clear_bit(p->prio, array->bitmap);

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