From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932480AbaKMKVj (ORCPT ); Thu, 13 Nov 2014 05:21:39 -0500 Received: from relay.parallels.com ([195.214.232.42]:45586 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932298AbaKMKVh (ORCPT ); Thu, 13 Nov 2014 05:21:37 -0500 Message-ID: <1415874091.15631.44.camel@tkhai> Subject: Re: [PATCH v5] sched/deadline: support dl task migration during cpu hotplug From: Kirill Tkhai To: Wanpeng Li CC: Wanpeng Li , Ingo Molnar , Peter Zijlstra , Juri Lelli , Date: Thu, 13 Nov 2014 13:21:31 +0300 In-Reply-To: <546485A2.7050501@gmail.com> References: <1415754413-13988-1-git-send-email-wanpeng.li@linux.intel.com> <1415809626.15631.35.camel@tkhai> <20141112225636.GA23249@kernel> <1415873444.15631.42.camel@tkhai> <546485A2.7050501@gmail.com> Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org В Чт, 13/11/2014 в 18:19 +0800, Wanpeng Li пишет: > Hi Kirill, > On 11/13/14, 6:10 PM, Kirill Tkhai wrote: > > В Чт, 13/11/2014 в 06:56 +0800, Wanpeng Li пишет: > >> Hi Kirill, > >> On Wed, Nov 12, 2014 at 07:27:06PM +0300, Kirill Tkhai wrote: > >>> В Ср, 12/11/2014 в 09:06 +0800, Wanpeng Li пишет: > >>>> 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. > >>>> > >>>> The method to reproduce: > >>>> schedtool -E -t 50000:100000 -e ./test > >>>> Actually test is just a simple for loop. Then observe which cpu the test > >>>> task is on. > >>>> echo 0 > /sys/devices/system/cpu/cpuN/online > >>>> > >>>> This patch adds the dl task migration during cpu hotplug by finding a most > >>>> suitable later deadline rq after dl timer fire if current rq is offline, > >>>> if fail to find a suitable later deadline rq then fallback to any eligible > >>>> online cpu in order that the deadline task will come back to us, and the > >>>> push/pull mechanism should then move it around properly. > >>>> > >>>> Signed-off-by: Wanpeng Li > >>>> --- > >>>> v4 -> v5: > >>>> * remove raw_spin_unlock(&rq->lock) > >>>> * cleanup codes, spotted by Peterz > >>>> * cleanup patch description > >>>> v3 -> v4: > >>>> * use tsk_cpus_allowed wrapper > >>>> * fix compile error > >>>> v2 -> v3: > >>>> * don't get_task_struct > >>>> * if cannot preempt any rq, fallback to pick any online cpus > >>>> * use cpu_active_mask as original later_mask if cpu is offline > >>>> v1 -> v2: > >>>> * push the task to another cpu in dl_task_timer() if rq is offline. > >>>> > >>>> kernel/sched/deadline.c | 43 +++++++++++++++++++++++++++++++++++++++++-- > >>>> 1 file changed, 41 insertions(+), 2 deletions(-) > >>>> > >>>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > >>>> index f3d7776..7c31906 100644 > >>>> --- a/kernel/sched/deadline.c > >>>> +++ b/kernel/sched/deadline.c > >>>> @@ -487,6 +487,7 @@ static int start_dl_timer(struct sched_dl_entity *dl_se, bool boosted) > >>>> return hrtimer_active(&dl_se->dl_timer); > >>>> } > >>>> > >>>> +static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq); > >>>> /* > >>>> * This is the bandwidth enforcement timer callback. If here, we know > >>>> * a task is not on its dl_rq, since the fact that the timer was running > >>>> @@ -538,6 +539,43 @@ again: > >>>> update_rq_clock(rq); > >>>> dl_se->dl_throttled = 0; > >>>> dl_se->dl_yielded = 0; > >>>> + > >>>> + /* > >>>> + * So if we find that the rq the task was on is no longer > >>>> + * available, we need to select a new rq. > >>>> + */ > >>>> + if (unlikely(!rq->online)) { > >>>> + struct rq *later_rq = NULL; > >>>> + > >>>> + later_rq = find_lock_later_rq(p, rq); > >>>> + > >>>> + if (!later_rq) { > >>>> + int cpu; > >>>> + > >>>> + /* > >>>> + * If cannot preempt any rq, fallback to pick any > >>>> + * online cpu. > >>>> + */ > >>>> + cpu = cpumask_any_and(cpu_active_mask, > >>>> + tsk_cpus_allowed(p)); > >>>> + if (cpu >= nr_cpu_ids) { > >>>> + pr_warn("fail to find any online cpu and task will never come back\n"); > >>>> + goto unlock; > >>>> + } > >>>> + later_rq = cpu_rq(cpu); > >>> later_rq is not locked here, but you activate p on it and you do unlock below. > >> Great catch! How about add double_lock_balance(rq, later_rq); here? > > This sounds good. > > I will do this in next version. ;-) > > > > >> Regards, > >> Wanpeng Li > >> > >>>> + } > >>>> + > >>>> + deactivate_task(rq, p, 0); > >>>> + set_task_cpu(p, later_rq->cpu); > >>>> + activate_task(later_rq, p, 0); > >>> ^^^^^ > >>> > >>>> + > >>>> + resched_curr(later_rq); > >>>> + > >>>> + double_unlock_balance(rq, later_rq); > >>> ^^^^^^ > >>> > >>>> + > >>>> + goto unlock; > >>>> + } > >>>> + > >>>> if (task_on_rq_queued(p)) { > >>>> enqueue_task_dl(rq, p, ENQUEUE_REPLENISH); > >>>> if (dl_task(rq->curr)) > >>>> @@ -1185,8 +1223,9 @@ static int find_later_rq(struct task_struct *task) > >>>> * We have to consider system topology and task affinity > >>>> * first, then we can look for a suitable cpu. > >>>> */ > >>>> - cpumask_copy(later_mask, task_rq(task)->rd->span); > >>>> - cpumask_and(later_mask, later_mask, cpu_active_mask); > >>>> + cpumask_copy(later_mask, cpu_active_mask); > >>>> + if (likely(task_rq(task)->online)) > >>>> + cpumask_and(later_mask, later_mask, task_rq(task)->rd->span); > >>>> cpumask_and(later_mask, later_mask, &task->cpus_allowed); > >>>> best_cpu = cpudl_find(&task_rq(task)->rd->cpudl, > >>>> task, later_mask); > > Also, we should think about the following situation. > > > > DL task is left on dead rq. In your scheme it will be moved by the timer. > > But what will be if somebody changes the class of the task (before timer)? > > I think timer will be cancelled in switched_from_dl(). Yeah, but nobody will move this task to alive rq. > > Regards, > Wanpeng Li > > > In this case the task still remains on dead rq. > > > > We should handle this situation in some way. > > > > Kirill > > > > > > -- > > 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/ >