linux-kernel - Re: [PATCH 7/9 V3] workqueue: explicit way to wait for idles workers to finish

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Message-ID: <20120829183447.GC2258@dhcp-172-17-108-109.mtv.corp.google.com>
Date:	Wed, 29 Aug 2012 11:34:47 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/9 V3] workqueue: explicit way to wait for idles
 workers to finish

Hello,

On Thu, Aug 30, 2012 at 12:51:58AM +0800, Lai Jiangshan wrote:
> busy_worker_rebind_fn() can't return until all idle workers are rebound.
> This order is ensured by rebind_workers() currently.
> 
> We use mutex_lock(&worker->pool->manager_mutex) to wait for all idle workers
> to be rebound. this is an explicit way and it will ease the pain of
> the rebind_workers().
> 
> The sleeping mutex_lock(&worker->pool->manager_mutex) must be put in the top of
> busy_worker_rebind_fn(), because this busy worker thread can sleep
> before the WORKER_REBIND is cleared, but can't sleep after
> the WORKER_REBIND cleared.

I really can't say I like this overloading of manager_mutex.  CPU
up/down are actually behaving like the manager while it's holding the
manager_mutex at least.  I don't really think this
non-manager-role-manager-mutex usage is worthwhile whatever
simplification it makes to rebind path.  Rebind path being a bit ugly
/ complex is better than it muddling non-cpu-hotplug path further.

Thanks.

-- 
tejun
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