Hi Peter,
On Mon, Nov 03, 2014 at 11:41:11AM +0100, Peter Zijlstra wrote:
>On Fri, Oct 31, 2014 at 03:28:17PM +0800, Wanpeng Li wrote:
>> Hi all,
>>
>> I observe that dl task can't be migrated to other cpus during cpu hotplug,
>> in
>> addition, task may/may not be running again if cpu is added back. The root
>> cause
>> which I found is that dl task will be throtted and removed from dl rq after
>> comsuming all budget, which leads to stop task can't pick it up from dl rq
>> and
>> migrate to other cpus during hotplug.
>>
>> So I try two methods.
>>
>> - add throttled dl sched_entity to a throttled_list, the list will be
>> traversed
>> during cpu hotplug, and the dl sched_entity will be picked and enqueue,
>> then
>> stop task will pick and migrate it. However, dl sched_entity is throttled
>> again
>> before stop task running since the below path. This path will set
>> rq->online 0
>> which lead to set_rq_offline() won't be called in function
>> migration_call().
>>
>
>This seems wrong to me; this screws around with the CBS by replenishing
>too soon.
Agreed.
>
>> @@ -1593,9 +1602,20 @@ static void rq_online_dl(struct rq *rq)
>> /* Assumes rq->lock is held */
>> static void rq_offline_dl(struct rq *rq)
>> {
>> + struct task_struct *p, *n;
>> +
>> if (rq->dl.overloaded)
>> dl_clear_overload(rq);
>>
>> + /* Make sched_dl_entity available for pick_next_task() */
>> + list_for_each_entry_safe(p, n, &rq->dl.throttled_list,
>> dl.throttled_node) {
>> + p->dl.dl_throttled = 0;
>> + hrtimer_cancel(&p->dl.dl_timer);
>> + p->dl.dl_runtime = p->dl.dl_runtime;
>> + if (task_on_rq_queued(p))
>> + enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
>> + }
>> +
>> cpudl_set(&rq->rd->cpudl, rq->cpu, 0, 0);
>> }
>
>
>So what is wrong with making dl_task_timer() deal with it? The timer
>will still fire on the correct time, canceling it and or otherwise
>messing with the CBS is wrong. Once it fires, all we need to do is
>migrate it to another cpu (preferably one that is still online of course
>:-).
Do you mean what I need to do is push the task to another cpu in
dl_task_timer()
if rq is offline? In addition, what will happen if dl task can't preempt on
another cpu?
Regards,
Wanpeng Li
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