From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934058AbbCPPBM (ORCPT ); Mon, 16 Mar 2015 11:01:12 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:37022 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752202AbbCPPBH (ORCPT ); Mon, 16 Mar 2015 11:01:07 -0400 Date: Mon, 16 Mar 2015 16:01:02 +0100 From: Ingo Molnar To: Wanpeng Li Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND v10] sched/deadline: support dl task migration during cpu hotplug Message-ID: <20150316150101.GA18521@gmail.com> References: <1426231647-11966-1-git-send-email-wanpeng.li@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1426231647-11966-1-git-send-email-wanpeng.li@linux.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * 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. > > Suggested-and-acked-by: Juri Lelli > Signed-off-by: Wanpeng Li > --- > kernel/sched/deadline.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 54 insertions(+) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 5cb5c9c..db457b9 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 +538,59 @@ 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. s/If cannot/If we cannot s/fallback/fall back > + */ > + fallback = true; > + cpu = cpumask_any_and(cpu_active_mask, > + tsk_cpus_allowed(p)); shouldn't be on separate lines - but this is also a sign that the guts of this new code should be in a helper function, not inside several layers of branches. > + if (cpu >= nr_cpu_ids) { > + if (dl_bandwidth_enabled()) { > + /* > + * Fail to find any suitable cpu. > + * The task will never come back! > + */ > + WARN_ON(1); Can this condition happen to users with a non-buggy kernel? Thanks, Ingo