linux-kernel - Re: [PATCHSET] workqueue: implement and use WQ

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Date:	Wed, 21 Jul 2010 17:31:00 +0200
From:	Tejun Heo <tj@...nel.org>
To:	David Howells <dhowells@...hat.com>
CC:	Arjan van de Ven <arjan@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	torvalds@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, oleg@...hat.com, axboe@...nel.dk,
	dwalker@...eaurora.org, stefanr@...6.in-berlin.de,
	florian@...kler.org, andi@...stfloor.org, mst@...hat.com,
	randy.dunlap@...cle.com, Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCHSET] workqueue: implement and use WQ_UNBOUND

Hello,

On 07/21/2010 05:25 PM, David Howells wrote:
>> Each gcwq keeps track of currently running works in a hash table and looks
>> whether the work in question is already executing before starting executing
>> it.  It's a bit complex but as a work_struct may be freed once execution
>> starts, the status needs to be tracked outside.
> 
> Thanks, that's what I wanted to know.
> 
> I presume this survives an executing work_struct being freed, reallocated and
> requeued before the address of the work_struct is removed from the hash table?

It will unnecessarily stall the execution of the new work if the last
work is still running but nothing will be broken correctness-wise.

> I can see at least one way of doing this: marking the work_struct address in
> the hash when the address becomes pending again so that the process of hash
> removal will cause the work_struct to be requeued automatically.

If I'm correctly understanding what you're saying, the code already
does about the same thing.

Thanks.

-- 
tejun
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