Messages in this thread Patch in this message | | | Date | Tue, 04 Nov 2014 21:30:46 +0800 | From | Wanpeng Li <> | Subject | Re: [PATCH RFC] sched/deadline: support dl task migrate during cpu hotplug |
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Hi Peter, On 14/11/4 下午6:10, Peter Zijlstra wrote: > On Tue, Nov 04, 2014 at 04:23:45PM +0800, Wanpeng Li wrote: >> On Tue, Nov 04, 2014 at 09:32:25AM +0100, Peter Zijlstra wrote: >>> On Tue, Nov 04, 2014 at 07:57:48AM +0800, Wanpeng Li wrote: >>>> 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: >>>>> 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? >>> That does indeed appear to be the sensible fix to me. >>> >>>> In addition, what will happen if dl task can't preempt on >>>> another cpu? >>> So if we find that the rq the task was on is no longer available, we >>> need to select a new rq, the 'right' rq would be the one running the >>> latest deadline. >>> >>> If it cannot preempt the latest (running) deadline, it was not eligible >>> for running in the first place so no worries, right? >> I think this will lead to this deadline task cannot running on any rqs any more. >> If my understanding is not right, when it will be picked? > So you unconditionally place it on the rq with the latest deadline. If > it cannot preempt, at least its on an online cpu. It will get scheduled > whenever its deadline is one of the N earliest, with N the number of > online CPUs.
If something like this make sense?
(Will test it tomorrow and send out a formal one) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index f3d7776..dac33d1 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -553,6 +553,41 @@ again: push_dl_task(rq); #endif } + + /* + * So if we find that the rq the task was on is no longer + * available, we need to select a new rq, the 'right' rq + * would be the one running the latest deadline. + * + * If it cannot preempt, at least it's on an online cpu. It + * will get scheduled whenever its deadline is one of the N + * earliest, with N the number of online CPUs. + */ + + if (!rq->online) { + struct rq *latest_rq = NULL; + int cpu; + u64 dmin = LONG_MAX; + + for_each_cpu(cpu, &p->cpus_allowed) + if (cpu_online(cpu) && + cpu_rq(cpu)->dl.earliest_dl.curr < dmin) { + latest_rq = cpu_rq(cpu); + dmin = latest_rq->dl.earliest_dl.curr; + } + + if (!latest_rq) + goto unlock; + + raw_spin_lock(&latest_rq->lock); + + deactivate_task(rq, p, 0); + set_task_cpu(p, latest_rq->cpu); + activate_task(latest_rq, p, 0); + + raw_spin_unlock(&latest_rq->lock); + } + unlock: raw_spin_unlock(&rq->lock);
Regards, Wanpeng Li
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