From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752352AbaKLAOJ (ORCPT ); Tue, 11 Nov 2014 19:14:09 -0500 Received: from mga01.intel.com ([192.55.52.88]:50619 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbaKLAOG (ORCPT ); Tue, 11 Nov 2014 19:14:06 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.07,362,1413270000"; d="scan'208";a="630447662" Date: Wed, 12 Nov 2014 07:53:20 +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: <20141111235320.GA3946@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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1415711354.15631.15.camel@tkhai> 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 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. 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/ >> >