From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755395AbaKSNtC (ORCPT ); Wed, 19 Nov 2014 08:49:02 -0500 Received: from service87.mimecast.com ([91.220.42.44]:51504 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751547AbaKSNtA convert rfc822-to-8bit (ORCPT ); Wed, 19 Nov 2014 08:49:00 -0500 Message-ID: <546C9FE0.9010407@arm.com> Date: Wed, 19 Nov 2014 13:49:20 +0000 From: Juri Lelli User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Wanpeng Li , Wanpeng Li , Ingo Molnar , Peter Zijlstra CC: Kirill Tkhai , "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> <546377FC.4090408@arm.com> <546BD3DB.7050207@gmail.com> <546C6D53.2020007@arm.com> <546C8D7C.4040808@gmail.com> In-Reply-To: <546C8D7C.4040808@gmail.com> X-OriginalArrivalTime: 19 Nov 2014 13:48:55.0870 (UTC) FILETIME=[8FD9BDE0:01D003FF] X-MC-Unique: 114111913485800801 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 19/11/14 12:30, Wanpeng Li wrote: > Hi Juri, > On 11/19/14, 6:13 PM, Juri Lelli wrote: >> Hi, >> >> On 18/11/14 23:18, Wanpeng Li wrote: >>> Hi Juri, >>> On 11/12/14, 11:08 PM, Juri Lelli wrote: >>>> Hi, >>>> >>>> On 12/11/14 01:06, Wanpeng Li wrote: >>>>> 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); >>>>> + } >>>>> + >>>>> + 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); >>>> So, here you consider the span only when the task_rq is online, >>>> but there might be others cpus still online belonging to the same >>>> rd->span. And you have to consider them when migrating. Actually, >>>> migration must still be restricted to the online cpus of task's >>>> original rd->span, or I fear you can break clustered scheduling. >>> Sorry, what's clustered scheduling? >>> >> It's a scheduling configuration in which you restrict tasks to run in >> disjoint subsets of system CPUs. Translated to what we have, it's what >> you get when you create exclusive cpusets (each one gets a rd) and >> associate tasks to them. >> >> My concern in what above is that you may end up breaking this setup >> if you don't consider the sd->span when one of the CPUs of your >> cpuset is off. But, Pang Xunlei patches may solve this, I still have to >> check :/. > > Thanks for your explanation. Could you point out which one of Pang's > patchset solve this? ;-) > https://lkml.org/lkml/2014/11/17/443 may help with this, although I still have to properly look at it. Best, - Juri > Regards, > Wanpeng Li > >> >> Thanks, >> >> - Juri >> >>> Regards, >>> Wanpeng Li >>> >>>> Thanks, >>>> >>>> - Juri >>>> >>>>> cpumask_and(later_mask, later_mask, &task->cpus_allowed); >>>>> best_cpu = cpudl_find(&task_rq(task)->rd->cpudl, >>>>> task, later_mask); >>>>> >>>> -- >>>> 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/ >>> > >