From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754323AbbCECD6 (ORCPT ); Wed, 4 Mar 2015 21:03:58 -0500 Received: from mga09.intel.com ([134.134.136.24]:50628 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751820AbbCECD5 (ORCPT ); Wed, 4 Mar 2015 21:03:57 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,344,1422950400"; d="scan'208";a="675346442" Date: Thu, 5 Mar 2015 09:45:21 +0800 From: Wanpeng Li To: Juri Lelli Cc: Wanpeng Li , Ingo Molnar , Peter Zijlstra , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v9] sched/deadline: support dl task migration during cpu hotplug Message-ID: <20150305014521.GA3112@kernel> Reply-To: Wanpeng Li References: <1425339349-3321-1-git-send-email-wanpeng.li@linux.intel.com> <54F6D60F.8020502@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54F6D60F.8020502@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, Mar 04, 2015 at 09:53:19AM +0000, Juri Lelli wrote: >Hi, > >I think we are still missing a corner case: no admission control, a task >with an affinity mask of a single cpu, the cpu goes off. In this case we >could try to let it run just somewhere else, as we don't guarantee anything >from start. This applies on top of your patch, comments? > >Thanks, > >- Juri > >--- > kernel/sched/deadline.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > >diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >index 467ec5d..8dec157 100644 >--- a/kernel/sched/deadline.c >+++ b/kernel/sched/deadline.c >@@ -579,10 +579,24 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) > * online cpu. > */ > fallback = true; >- cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p)); >+ cpu = cpumask_any_and(cpu_active_mask, >+ tsk_cpus_allowed(p)); Indeed, otherwise "WARNING: line over 80 characters", I will change it back in next version. > if (cpu >= nr_cpu_ids) { >- WARN_ON(1); >- goto unlock; >+ if (dl_bandwidth_enabled()) { >+ /* >+ * Fail to find any suitable cpu. >+ * The task will never come back! >+ */ >+ WARN_ON(1); >+ goto unlock; >+ } else { >+ /* >+ * If admission control is disabled we >+ * try a little harder to let the task >+ * run. >+ */ >+ cpu = cpumask_any(cpu_active_mask); >+ } Cool, I will fold this next branch in my patch, your help is a great appreciated. ;-) Regards, Wanpeng Li > } > later_rq = cpu_rq(cpu); > double_lock_balance(rq, later_rq); >-- >2.3.0 > >On 02/03/2015 23:35, 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 >> --- >> v8 -> v9: >> * align tsk_cpus_allowed(p) to cpu_active_mask >> * add WARN_ON(1) >> * don't resched_curr if later_rq come from the cpumask_any_and() >> 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 | 40 ++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 40 insertions(+) >> >> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c >> index 08766a3..d5b1b16 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 +538,45 @@ 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; >> + bool fallback = false; >> + >> + later_rq = find_lock_later_rq(p, rq); >> + >> + if (!later_rq) { >> + int cpu; >> + >> + /* >> + * If cannot preempt any rq, fallback to pick any >> + * online cpu. >> + */ >> + fallback = true; >> + cpu = cpumask_any_and(cpu_active_mask, tsk_cpus_allowed(p)); >> + if (cpu >= nr_cpu_ids) { >> + WARN_ON(1); >> + 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); >> + >> + if (!fallback) >> + resched_curr(later_rq); >> + >> + double_unlock_balance(rq, later_rq); >> + >> + goto unlock; >> + } >> + >> + /* >> * If the throttle happened during sched-out; like: >> * >> * schedule() >>