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From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	Jens Axboe <jaxboe@fusionio.com>
Subject: Re: [RFC][PATCH 2/3] sched, workqueue: Move WQ-sleeper wakeup
Date: Wed, 22 Jun 2011 11:37:06 +0200	[thread overview]
Message-ID: <20110622093706.GB30101@htj.dyndns.org> (raw)
In-Reply-To: <1308734848.1022.16.camel@twins>

On Wed, Jun 22, 2011 at 11:27:28AM +0200, Peter Zijlstra wrote:
> On Wed, 2011-06-22 at 11:24 +0200, Tejun Heo wrote:
> > Preemption could still be enabled here, right?  What prevents
> > preemtion kicking after wq_worker_sleeping() and do it again thus
> > breaking nr_running tracking.
> 
> Aren't all PF_WQ_WORKER threads cpu-bound?

Hmmm... I don't see how that would matter.  Please consider the
following scenario.

* A work item calls schedule() for whatever reason.

* schedule() calls sched_submit_work() which in turn calls
  wq_worker_sleeping() which adjusts nr_running.  All this happens
  with preemption enabled.

* sched_submit_work() returns but before schedule() does
  preempt_disable(), an IRQ is delivered.  By the time IRQ return path
  is executed, TIF_NEED_RESCHED is set which in turn calls schedule()
  again and repeats the above two steps for the same worker.

Thanks.

-- 
tejun

  reply	other threads:[~2011-06-22  9:37 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-21 23:34 [RFC][PATCH 0/3] Move WQ,unplug scheduler hooks Peter Zijlstra
2011-06-21 23:34 ` [RFC][PATCH 1/3] sched, block: Move unplug Peter Zijlstra
2011-06-22  7:01   ` Jens Axboe
2011-06-22 13:53     ` Thomas Gleixner
2011-06-22 14:01       ` Jens Axboe
2011-06-22 14:30         ` Thomas Gleixner
2011-06-22 14:38           ` Peter Zijlstra
2011-06-22 15:08             ` Vivek Goyal
2011-06-22 16:04               ` Jens Axboe
2011-06-21 23:34 ` [RFC][PATCH 2/3] sched, workqueue: Move WQ-sleeper wakeup Peter Zijlstra
2011-06-22  9:24   ` Tejun Heo
2011-06-22  9:27     ` Peter Zijlstra
2011-06-22  9:37       ` Tejun Heo [this message]
2011-06-22 13:47     ` Thomas Gleixner
2011-06-21 23:34 ` [RFC][PATCH 3/3] block: Break long IRQ disabled region Peter Zijlstra
2011-06-22  7:03   ` Jens Axboe

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