Re: Question: RT schedular : task_tick_rt(struct rq *rq, struct task_struct *p) : decreases overhead when rq->nr_running == 1

["Dmitry Adamushko" <dmitry.adamushko@gmail.com>]

On 09/08/07, Ingo Molnar <mingo@elte.hu> wrote:
>
> FYI, that's the patch i applied:

Thanks. Added my SOB below.

>
> --------------------------->
> Subject: sched: optimize task_tick_rt() a bit
> From: Dmitry Adamushko <dmitry.adamushko@gmail.com>
>
> Mitchell Erblich suggested a change to not requeue SCHED_RR
> tasks if there's only a single task on the runqueue, by
> checking for rq->nr_running == 1.
>
> provide a more efficient implementation of that, to check that
> particular RT priority-queue only.
>
> [ From: mingo@elte.hu ]
>
> Also first requeue the task then set need_resched - results
> in slightly better machine-instruction ordering. Also clean
> up the code a bit.
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>


Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>


> ---
>  kernel/sched_rt.c |   11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> Index: linux/kernel/sched_rt.c
> ===================================================================
> --- linux.orig/kernel/sched_rt.c
> +++ linux/kernel/sched_rt.c
> @@ -207,10 +207,15 @@ static void task_tick_rt(struct rq *rq,
>                 return;
>
>         p->time_slice = static_prio_timeslice(p->static_prio);
> -       set_tsk_need_resched(p);
>
> -       /* put it at the end of the queue: */
> -       requeue_task_rt(rq, p);
> +       /*
> +        * Requeue to the end of queue if we are not the only element
> +        * on the queue:
> +        */
> +       if (p->run_list.prev != p->run_list.next) {
> +               requeue_task_rt(rq, p);
> +               set_tsk_need_resched(p);
> +       }
>  }
>
>  static struct sched_class rt_sched_class __read_mostly = {
>


-- 
Best regards,
Dmitry Adamushko