Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753809AbaKLXnS (ORCPT ); Wed, 12 Nov 2014 18:43:18 -0500 Received: from mga11.intel.com ([192.55.52.93]:42988 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753475AbaKLXnQ (ORCPT ); Wed, 12 Nov 2014 18:43:16 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,372,1413270000"; d="scan'208";a="621501669" Date: Thu, 13 Nov 2014 07:22:32 +0800 From: Wanpeng Li To: Juri Lelli Cc: Wanpeng Li , Ingo Molnar , Peter Zijlstra , Kirill Tkhai , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v5] sched/deadline: support dl task migration during cpu hotplug Message-ID: <20141112232232.GC23249@kernel> Reply-To: Wanpeng Li References: <1415754413-13988-1-git-send-email-wanpeng.li@linux.intel.com> <546377FC.4090408@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <546377FC.4090408@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Juri, On Wed, Nov 12, 2014 at 03:08:44PM +0000, Juri Lelli wrote: Btw, could you review other three deadline patches of mine? https://lkml.org/lkml/2014/11/6/51 https://lkml.org/lkml/2014/11/10/817 https://lkml.org/lkml/2014/11/10/818 Great thanks for your time. ;-) Regards, Wanpeng Li >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); >> -- 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/