Hi Dmitry,
>>> On Sun, Dec 9, 2007 at 12:16 PM, in message
<[email protected]>, "Dmitry
Adamushko" <[email protected]> wrote:
> [ cc'ed lkml ]
>
> I guess, one possible load-balancing point is out of consideration --
> sched_setscheduler()
> (also rt_mutex_setprio()).
>
> (1) NORMAL --> RT, when p->se.on_rq == 1 && ! task_running(rq, p)
>
> (2) RT --> NORMAL, when task_running(rq, p) == 1
>
> e.g. for (2) we may even get a completely idle rq (schedule() -->
> schedule_balance_rt() will not help due to schedule_balance_rt()
> having a rt_task(prev) check in place... and 'prev' is of NORMAL type
> when it's scheduled out).
Indeed. I think you are correct on both counts. This is an oversight, so good eyes!
>
>
> btw., both cases would be addressed by placing load-balance points
> into sched_class_rt->{enqueue,dequeue}_task_rt()... push_rt_tasks()
> and pull_rt_tasks() respectively. As a side effect (I think,
> technically, it would be possible), 3 out of 4 *_balance_rt() calls
> (the exception: schedule_tail_balance_rt()) in schedule() would become
> unnecessary.
>
> _BUT_
>
> the enqueue/dequeue() interface would become less straightforward,
> logically-wise.
> Something like:
>
> rq = activate_task(rq, ...) ; /* may unlock rq and lock/return another one
> */
>
> would complicate the existing use cases.
>
I think I would prefer to just fix the setscheduler/setprio cases for the class transition than change the behavior of these enqueue/dequeue calls. But I will keep an open mind as I look into this issue.
Thanks for the review!
-Greg
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