From: Peter Zijlstra <peterz@infradead.org>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Wanpeng Li <wanpeng.li@hotmail.com>,
Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@arm.com>,
Luca Abeni <luca.abeni@unitn.it>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH] sched: fix the intention to re-evalute tick dependency for offline cpu
Date: Thu, 11 Aug 2016 16:45:11 +0200 [thread overview]
Message-ID: <20160811144511.GR6879@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1470304280-3917-1-git-send-email-wanpeng.li@hotmail.com>
On Thu, Aug 04, 2016 at 05:51:20PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> The dl task will be replenished after dl task timer fire and start a new
> period. It will be enqueued and to re-evaluate its dependency on the tick
> in order to restart it. However, if cpu is hot-unplug, irq_work_queue will
> splash since the target cpu is offline.
>
> As a result:
>
> WARNING: CPU: 2 PID: 0 at kernel/irq_work.c:69 irq_work_queue_on+0xad/0xe0
> Call Trace:
> dump_stack+0x99/0xd0
> __warn+0xd1/0xf0
> warn_slowpath_null+0x1d/0x20
> irq_work_queue_on+0xad/0xe0
> tick_nohz_full_kick_cpu+0x44/0x50
> tick_nohz_dep_set_cpu+0x74/0xb0
> enqueue_task_dl+0x226/0x480
> activate_task+0x5c/0xa0
> dl_task_timer+0x19b/0x2c0
> ? push_dl_task.part.31+0x190/0x190
Hurm, so this is after hot-unplug succeeded. We get a timer (which is
also already migrated), but we enqueue the dl task on the offline CPU,
because we need to do replenish because start_dl_timer() -- see the
comment in dl_task_timer() at #ifdef CONFIG_SMP.
Then, once we've enqueued the task on the offline cpu, do we migrate it.
Bit icky that, but I don't immediately see a better way.
And I think you're right in that we don't leak the nohz state, the
migration, which we do immediately after this, takes care of that.
Juri, any opinions?
next prev parent reply other threads:[~2016-08-11 14:45 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-04 9:51 [PATCH] sched: fix the intention to re-evalute tick dependency for offline cpu Wanpeng Li
2016-08-05 5:36 ` Wanpeng Li
2016-08-10 12:43 ` Frederic Weisbecker
2016-08-10 13:23 ` Wanpeng Li
2016-08-10 18:53 ` Frederic Weisbecker
2016-08-11 1:36 ` Wanpeng Li
2016-08-11 14:45 ` Peter Zijlstra [this message]
2016-08-11 14:57 ` Frederic Weisbecker
2016-08-11 15:14 ` Juri Lelli
2016-08-11 22:35 ` Wanpeng Li
2016-08-26 9:27 ` Wanpeng Li
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