Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932501AbaKMKTd (ORCPT ); Thu, 13 Nov 2014 05:19:33 -0500 Received: from mail-pd0-f173.google.com ([209.85.192.173]:34398 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932290AbaKMKTa (ORCPT ); Thu, 13 Nov 2014 05:19:30 -0500 Message-ID: <546485A2.7050501@gmail.com> Date: Thu, 13 Nov 2014 18:19:14 +0800 From: Wanpeng Li User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Kirill Tkhai , Wanpeng Li CC: Ingo Molnar , Peter Zijlstra , Juri Lelli , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5] sched/deadline: support dl task migration during cpu hotplug 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> In-Reply-To: <1415873444.15631.42.camel@tkhai> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(). 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/ -- 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/