lkml.org 
[lkml]   [2011]   [Mar]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [BUGFIX][PATCH] Fix sched rt group scheduling when hierachy is enabled
From
On Fri, Mar 4, 2011 at 2:02 PM, Yong Zhang <yong.zhang0@gmail.com> wrote:
> On Fri, Mar 4, 2011 at 3:25 PM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>> * Yong Zhang <yong.zhang0@gmail.com> [2011-03-04 11:43:16]:
>>
>>> On Thu, Mar 3, 2011 at 11:29 PM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>>> > No, not really :) It is required, it is a backup check to see if we
>>> > have queued tasks, rt_time of 0 and the runqueue is not throttled, why
>>> > should it be dequeued?
>>>
>>> But I can't see where that kind of rt_rq is dequeued, mind pointing it out?
>>>
>>
>> So here is what I saw
>>
>> 1. sched_dequeue_stack called from the dequeue path dequeues the
>> queues and sets rt_nr_running to 0
>> 2. Enqueuing fails because rt_throttled is set for the group_rq
>> (parent who is throttled)
>> 3. This causes further enqueue to fail, since rt_nr_running did
>> not increment in step 2
>
> Whose rt_nr_running? group_rq's or parent of group_rq?
> For parent of group_rq, yes.
> For group_rq's, no, because we don't touch its rt_nr_running.
>

For parent of group_rq

>
>> , eventually the timer decrements rt_time
>> to 0 and the task is never picked up.
>
> If I understand correctly, you mean this:
>
> For a group(A) which has one task(b) attached but A is throttled,so
> A is unqueued now
> A.throttled == 1 && A.rt_nr_running == 1
>  deactivate_task(b); /* A.throttled == 1 && A.rt_nr_running == 0 */
>    do_sched_rt_period_timer(); /* A.run_time == 0 && A.throttled == 0*/

Note at some point rt_time becomes 0 and if enqueue is not set, the
next do_sched_rt_period_timer() is a NOP and does not enqueue back the
group

Balbir
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-03-04 09:39    [W:0.811 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site