Re: [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Libo Chen <chenlibo.3@gmail.com>]

From: Libo Chen <libo.chen@huawei.com>


On 2013-1-29 4:23, Kirill Tkhai wrote:
> Just switched pinned task is not able to be pushed. If the rq had had
> several RT tasks before they have already been considered as candidates
> to be pushed (or pulled).
>
> Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Ingo Molnar <mingo@kernel.org>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: linux-rt-users <linux-rt-users@vger.kernel.org>
> ---
>  kernel/sched/rt.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4e8f0f4..5f7d92b 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>  	 */
>  	if (p->on_rq && rq->curr != p) {
>  #ifdef CONFIG_SMP
> -		if (rq->rt.overloaded && push_rt_task(rq) &&
> +		if (rq->rt.overloaded && p->nr_cpus_allowed > 1 &&
>  		    /* Don't resched if we changed runqueues */
> -		    rq != task_rq(p))
> +		    push_rt_task(rq) && rq != task_rq(p))

I think you worry about it was excess to call push_rt_task, since the task of p->nr_cpus_allowed=1 can`t be pushed. is that right?

The task of p->nr_cpus_allowed =1 would`t be added to  pushable_tasks list （see the enqueue_task_rt()）and  this push_rt_task() need to push other tasks when rt.overloaded.

So I don`t agree this patch.  


>  			check_resched = 0;
>  #endif /* CONFIG_SMP */
>  		if (check_resched && p->prio < rq->curr->prio)
> --
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