linux-kernel - Re: [PATCHSET wq/for-3.10] workqueue: break up workqueue

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Message-ID: <20130320143832.GT3042@htj.dyndns.org>
Date:	Wed, 20 Mar 2013 07:38:32 -0700
From:	Tejun Heo <tj@...nel.org>
To:	JoonSoo Kim <js1304@...il.com>
Cc:	linux-kernel@...r.kernel.org, laijs@...fujitsu.com
Subject: Re: [PATCHSET wq/for-3.10] workqueue: break up workqueue_lock into
 multiple locks

Hey,

On Wed, Mar 20, 2013 at 11:01:50PM +0900, JoonSoo Kim wrote:
> 2013/3/19 Tejun Heo <tj@...nel.org>:
> > On Wed, Mar 13, 2013 at 07:57:18PM -0700, Tejun Heo wrote:
> >> and available in the following git branch.
> >>
> >>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git review-finer-locking
> >
> > Applied to wq/for-3.10.
> 
> Hello, Tejun.
> 
> I know I am late, but, please give me a change to ask a question.
> 
> Finer locking for workqueue code is really needed?
> Is there a performance issue?
> I think that there is too many locks and locking rules,
> although the description about these are very nice.

It isn't about performance.  So, workqueue_lock is broken into three
locks by this series - wq_mutex, pwq_lock and mayday_lock.  The
primary reason for this patchset is wq_mutex.  We want to do blocking
operations while excluding workqueue and pool modifications which
isn't possible with workqueue_lock and at the same time there are
things which can't be protected by a mutex (should be a irq-safe
lock), so we need break up the lock.  After breaking off wq_mutex from
workqueue_lock.  Most stuff covered by workqueue_lock was pwq related
and mayday was the only one-off thing left, so one more lock there,
which I think actually make things easier to digest.

Thanks.

-- 
tejun
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