From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754233AbaKSMbC (ORCPT ); Wed, 19 Nov 2014 07:31:02 -0500 Received: from mail-pd0-f181.google.com ([209.85.192.181]:59557 "EHLO mail-pd0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754007AbaKSMbA (ORCPT ); Wed, 19 Nov 2014 07:31:00 -0500 Message-ID: <546C8D7C.4040808@gmail.com> Date: Wed, 19 Nov 2014 20:30:52 +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: Juri Lelli , 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> In-Reply-To: <546C6D53.2020007@arm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? ;-) 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/ >>