Re: [PATCH 1/2] sched: push rt tasks only if newly activated tasks have been added

Dmitry Adamushko
2008-04-23T10:23:36Z

2008/4/23 Gregory Haskins <ghaskins@novell.com>:
> [ ... ]
>
> I think we can simplify this further. We really only need to push here if we are not going to reschedule anytime soon (probably white-space damaged):
>
>
> --- a/kernel/sched_rt.c
>
> +++ b/kernel/sched_rt.c
> @@ -1058,11 +1058,14 @@ static void post_schedule_rt(struct rq *rq)
> }
> }
>
> -
> +/*
> + * If we are not running and we are not going to reschedule soon, we should
> + * try to push tasks away now
> + */
>
> static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
> {
> if (!task_running(rq, p) &&
> - (p->prio >= rq->rt.highest_prio) &&
> + !test_tsk_thread_flag(rq->curr, TIF_NEED_RESCHED) &&
> rq->rt.overloaded)
> push_rt_tasks(rq);
> }

It's somewhat suboptimal as it doesn't guarantee that 'p' gets control next.

e.g. 2 tasks (T0 and T1) have been woken up before an actual
re-schedule takes place. Even if T1 is of lower prio than T0,
task_wake_up_rt() will see the NEED_RESCHED flag and bail out while it
would make sense at this moment to push T1 off this cpu.

p.s. hope you are better today. get well! :-)

--
Best regards,
Dmitry Adamushko