From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753543AbbCBMLz (ORCPT ); Mon, 2 Mar 2015 07:11:55 -0500 Received: from service87.mimecast.com ([91.220.42.44]:45217 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751237AbbCBMLw convert rfc822-to-8bit (ORCPT ); Mon, 2 Mar 2015 07:11:52 -0500 Message-ID: <54F45384.3000807@arm.com> Date: Mon, 02 Mar 2015 12:11:48 +0000 From: Juri Lelli User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Wanpeng Li , Ingo Molnar , Peter Zijlstra CC: "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v8] sched/deadline: support dl task migration during cpu hotplug References: <1424865005-103917-1-git-send-email-wanpeng.li@linux.intel.com> In-Reply-To: <1424865005-103917-1-git-send-email-wanpeng.li@linux.intel.com> X-OriginalArrivalTime: 02 Mar 2015 12:11:48.0411 (UTC) FILETIME=[0EF650B0:01D054E2] X-MC-Unique: 115030212115009601 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 25/02/2015 11:50, 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 > --- > v7 -> v8: > * remove rd->span related modification since Pang's commit 16b269436b72 > (sched/deadline: Modify cpudl::free_cpus to reflect rd->online) merged > upstream, which Juri pointed out can handle the exclusive cpusets. > * rebase > v6 -> v7: > * rebase > v5 -> v6: > * add double_lock_balance in the fallback path > 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 | 38 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 38 insertions(+) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 3fa8fa6..49f92c8 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -492,6 +492,7 @@ 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 > @@ -537,6 +538,43 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) > update_rq_clock(rq); > > /* > + * 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)); Please align this to cpu_active_mask above. > + if (cpu >= nr_cpu_ids) { > + pr_warn("fail to find any online cpu and task will never come back\n"); Wouldn't be better a WARN_ON(1) here? It is a pretty serious situation. > + goto unlock; > + } > + later_rq = cpu_rq(cpu); > + double_lock_balance(rq, later_rq); > + } > + > + deactivate_task(rq, p, 0); > + set_task_cpu(p, later_rq->cpu); > + activate_task(later_rq, p, ENQUEUE_REPLENISH); > + > + resched_curr(later_rq); Your later_rq can also come from the cpumask_any_and(), we should check if we need a resched here. Best, - Juri > + > + double_unlock_balance(rq, later_rq); > + > + goto unlock; > + } > + > + /* > * If the throttle happened during sched-out; like: > * > * schedule() >