From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753059AbaKLPIc (ORCPT ); Wed, 12 Nov 2014 10:08:32 -0500 Received: from service87.mimecast.com ([91.220.42.44]:52476 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752377AbaKLPIa convert rfc822-to-8bit (ORCPT ); Wed, 12 Nov 2014 10:08:30 -0500 Message-ID: <546377FC.4090408@arm.com> Date: Wed, 12 Nov 2014 15:08:44 +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 , 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> In-Reply-To: <1415754413-13988-1-git-send-email-wanpeng.li@linux.intel.com> X-OriginalArrivalTime: 12 Nov 2014 15:08:24.0849 (UTC) FILETIME=[817DF010:01CFFE8A] X-MC-Unique: 114111215082702601 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 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. Thanks, - Juri > cpumask_and(later_mask, later_mask, &task->cpus_allowed); > best_cpu = cpudl_find(&task_rq(task)->rd->cpudl, > task, later_mask); >