From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754380AbaKKLsV (ORCPT ); Tue, 11 Nov 2014 06:48:21 -0500 Received: from relay.parallels.com ([195.214.232.42]:44147 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753982AbaKKLKN (ORCPT ); Tue, 11 Nov 2014 06:10:13 -0500 Message-ID: <1415704209.15631.14.camel@tkhai> Subject: Re: [PATCH v4] sched/deadline: support dl task migration during cpu hotplug From: Kirill Tkhai To: Wanpeng Li CC: Ingo Molnar , Peter Zijlstra , Juri Lelli , Date: Tue, 11 Nov 2014 14:10:09 +0300 In-Reply-To: <1415673043-62281-1-git-send-email-wanpeng.li@linux.intel.com> References: <1415673043-62281-1-git-send-email-wanpeng.li@linux.intel.com> Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org В Вт, 11/11/2014 в 10:30 +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 fix it by push the task to another cpu in dl_task_timer() if > rq is offline. > > Signed-off-by: Wanpeng Li I'm still thinking we don't have to guarantee any "deadlines" during cpu hotplug... But, if speaking about this way: > --- > 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 | 51 ++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 48 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 00324af..e0fbba4 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 +539,46 @@ 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 (!rq->online) { > + struct rq *later_rq = NULL; > + > + raw_spin_unlock(&rq->lock); > + > + later_rq = find_lock_later_rq(p, rq); find_lock_later_rq() expects that rq is locked. The comment near its head confuses a reader. It locks newly found rq. > + > + if (!later_rq) { > + int cpu; > + > + /* > + * If cannot preempt any rq, fallback to pick any > + * online cpu. > + */ > + for_each_cpu(cpu, tsk_cpus_allowed(p)) > + if (cpu_online(cpu)) > + later_rq = cpu_rq(cpu); > + if (!later_rq) { > + pr_warn("fail to find any online and task " > + "will never come back to us\n"); > + goto out; > + } > + } > + > + 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); double_unlock_balance() unlocks later_rq only. > + > + goto out; > + } > + > if (task_on_rq_queued(p)) { > enqueue_task_dl(rq, p, ENQUEUE_REPLENISH); > if (dl_task(rq->curr)) > @@ -555,7 +596,7 @@ again: > } > unlock: > raw_spin_unlock(&rq->lock); > - > +out: > return HRTIMER_NORESTART; > } > > @@ -1185,8 +1226,12 @@ 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); > + if (likely(task_rq(task)->online)) { > + cpumask_copy(later_mask, task_rq(task)->rd->span); > + cpumask_and(later_mask, later_mask, cpu_active_mask); > + } else > + /* for offline cpus we have a singleton rd */ > + cpumask_copy(later_mask, cpu_active_mask); > cpumask_and(later_mask, later_mask, &task->cpus_allowed); > best_cpu = cpudl_find(&task_rq(task)->rd->cpudl, > task, later_mask);