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SubjectRe: [sched/rt] Optimization of function pull_rt_task()
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On Sun, 2012-04-15 at 23:45 +0400, Kirill Tkhai wrote:
> The condition (src_rq->rt.rt_nr_running) is weak because it doesn't
> consider the cases when src_rq has only processes bound to it (when
> single cpu is allowed). It may be running kernel thread like
> migration/x etc.
>
> So it's better to use more stronger condition which is able to exclude
> above conditions. The function has_pushable_tasks() complitely does
> this. A task may be pullable for another cpu rq only if he is pushable
> for his own queue.

I considered this before, and for some reason I never did the change.
I'll have to think about it. It seems like this would be the obvious
case, but I think there was something not so obvious that caused issues.
But I don't remember what it was.

I'll have to rethink this again.

Thanks,

-- Steve

>
> Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
> ---
> kernel/sched/rt.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index c5565c3..61e3086 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1729,7 +1729,7 @@ static int pull_rt_task(struct rq *this_rq)
> /*
> * Are there still pullable RT tasks?
> */
> - if (src_rq->rt.rt_nr_running <= 1)
> + if (!has_pushable_tasks(src_rq))
> goto skip;
>
> p = pick_next_highest_task_rt(src_rq, this_cpu);
>




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