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

From: Thomas Gleixner
Date: Wed Jul 11 2007 - 13:06:37 EST


On Wed, 2007-07-11 at 16:47 +0200, SÃbastien Duguà 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.
>
> SÃbastien.

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: SÃbastien Duguà <sebastien.dugue@xxxxxxxx>
>
> ---
> 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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