From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754588AbbCBXRp (ORCPT ); Mon, 2 Mar 2015 18:17:45 -0500 Received: from mga11.intel.com ([192.55.52.93]:44396 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753764AbbCBXRn (ORCPT ); Mon, 2 Mar 2015 18:17:43 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,678,1418112000"; d="scan'208";a="685847800" Date: Tue, 3 Mar 2015 06:59:25 +0800 From: Wanpeng Li To: Juri Lelli Cc: Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, Wanpeng Li Subject: Re: [PATCH v8] sched/deadline: support dl task migration during cpu hotplug Message-ID: <20150302225925.GA5807@kernel> Reply-To: Wanpeng Li References: <1424865005-103917-1-git-send-email-wanpeng.li@linux.intel.com> <54F45384.3000807@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54F45384.3000807@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 Mon, Mar 02, 2015 at 12:11:48PM +0000, Juri Lelli wrote: >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. Ok. > >> + 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. Good idea. > >> + 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. I will add the check in next version, great thanks for your review. ;-) Regards, Wanpeng Li > >Best, > >- Juri > >> + >> + double_unlock_balance(rq, later_rq); >> + >> + goto unlock; >> + } >> + >> + /* >> * If the throttle happened during sched-out; like: >> * >> * schedule() >>