Messages in this thread | | | Date | Tue, 04 Nov 2014 21:33:44 +0800 | From | Wanpeng Li <> | Subject | Re: [PATCH RFC] sched/deadline: support dl task migrate during cpu hotplug |
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On 14/11/4 下午9:30, Wanpeng Li wrote: > 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);
wow, sorry for mess format.
> > Regards, > Wanpeng Li > >> -- >> 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/ >
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