From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752404AbaKLAcv (ORCPT ); Tue, 11 Nov 2014 19:32:51 -0500 Received: from mga01.intel.com ([192.55.52.88]:30389 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751637AbaKLAcu (ORCPT ); Tue, 11 Nov 2014 19:32:50 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,364,1413270000"; d="scan'208";a="620864884" Date: Wed, 12 Nov 2014 08:12:15 +0800 From: Wanpeng Li To: Kirill Tkhai Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , linux-kernel@vger.kernel.org, Wanpeng Li Subject: Re: [PATCH v4] sched/deadline: support dl task migration during cpu hotplug Message-ID: <20141112001215.GB3946@kernel> Reply-To: Wanpeng Li References: <1415673043-62281-1-git-send-email-wanpeng.li@linux.intel.com> <1415704209.15631.14.camel@tkhai> <546209FD.8060102@gmail.com> <1415711354.15631.15.camel@tkhai> <20141111235320.GA3946@kernel> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20141111235320.GA3946@kernel> 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 On Wed, Nov 12, 2014 at 07:53:20AM +0800, Wanpeng Li wrote: >Hi Kirill, >On Tue, Nov 11, 2014 at 04:09:14PM +0300, Kirill Tkhai wrote: >>В Вт, 11/11/2014 в 21:07 +0800, Wanpeng Li пишет: >>> Hi Kirill, >>> On 11/11/14, 7:10 PM, Kirill Tkhai wrote: >>> > 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. >>> >>> Sorry for my bad, what's you think should be changed? >> >>raw_spin_unlock(&rq->lock) is wrong here. It's not need. >> > >The machine down after remove this. Just solve it, sorry for the noise. Regards, Wanpeng Li > >Regards, >Wanpeng Li > >>> >>> > >>> >> + >>> >> + 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); >>> > >>> > -- >>> > 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/ >>> >>