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SubjectRe: [RFC] sched: check RT runqueue overloaded in tick timer
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On Thu, 2011-06-30 at 20:47 +0800, Hillf Danton wrote:
> Hi Steven
>
> When tick timer runs, runqueue overload is checked. If overloaded and other
> CPUs available at the moment, reschedule is fired to allow push logic to move
> the pushable tasks somewhere else.

Why?

This would be a waste of overhead. We check when a task is queued and
dequeue, and when a cpu lowers its priority (for a pull). There's no
need to randomly check if we need to push or pull based on timers.
That's just going to slow things down.

-- Steve

>
> Thanks
>
> Hillf
> ---
> kernel/sched_rt.c | 21 +++++++++++++++++++--
> 1 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> index b03cd89..afd29a3 100644
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -1767,10 +1767,10 @@ static void task_tick_rt(struct rq *rq, struct
> task_struct *p, int queued)
> * FIFO tasks have no timeslices.
> */
> if (p->policy != SCHED_RR)
> - return;
> + goto check_overload;
>
> if (--p->rt.time_slice)
> - return;
> + goto check_overload;
>
> p->rt.time_slice = DEF_TIMESLICE;
>
> @@ -1782,6 +1782,23 @@ static void task_tick_rt(struct rq *rq, struct
> task_struct *p, int queued)
> requeue_task_rt(rq, p, 0);
> set_tsk_need_resched(p);
> }
> +
> +check_overload:
> +#ifdef CONFIG_SMP
> + if (!test_tsk_need_resched(p)) {
> + struct task_struct *t = pick_next_pushable_task(rq);
> + /*
> + * If @rq overloaded and other CPUs available, reschedule
> + * @p to allow the push logic to move the pushable tasks
> + * somewhere else.
> + *
> + * It is a pseudo schedule, since @p, without accident, will
> + * be picked again. If not, fine:)
> + */
> + if (t && cpupri_find(&rq->rd->cpupri, t, NULL))
> + set_tsk_need_resched(p);
> + }
> +#endif
> }
>
> static void set_curr_task_rt(struct rq *rq)




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