linux-kernel - Re: [PATCH 17/21] workqueue: simple reimplementation of SINGLE

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Message-ID: <4B02CB53.9020708@kernel.org>
Date:	Wed, 18 Nov 2009 01:12:03 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andy Walls <awalls@...ix.net>, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, jeff@...zik.org, mingo@...e.hu,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	peterz@...radead.org, andi@...stfloor.org, fweisbec@...il.com
Subject: Re: [PATCH 17/21] workqueue: simple reimplementation of SINGLE_THREAD
 workqueue

Hello, Linus.

11/18/2009 12:05 AM, Linus Torvalds wrote:
>> Do you think that usage is wide-spread?  Implementing strict ordering
>> shouldn't be too difficult but I can't help but feeling that such
>> assumption is abuse of implementation detail.
> 
> I think it would be good if it were more than an implementation detail, 
> and was something documented and known.
> 
> The less random and timing-dependent our interfaces are, the better off we 
> are. Guaranteeing that a single-threaded workqueue is done in order seems 
> to me to be a GoodThing(tm), regardless of whether much code depends on 
> it.
> 
> Of course, if there is some fundamental reason why it wouldn't be the 
> case, that's another thing. But if you think uit should be easy, and since 
> there _are_ users, then it shouldn't be seen as an "implementation 
> detail". It's a feature.

I might have been too early with the 'easy' part but I definitely can
give it a shot.  What do you think about the scheduler notifier
implementation?  It seems we'll end up with three callbacks.  It can
either be three hlist_heads in the struct_task linking each ops or
single hilst_head links ops tables (like the current preempt
notifiers).  Which one should I go with?

Thanks.

-- 
tejun
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