linux-kernel - Re: Overview of concurrency managed workqueue

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Message-ID: <4C18BF40.40607@kernel.org>
Date:	Wed, 16 Jun 2010 14:10:40 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Daniel Walker <dwalker@...eaurora.org>
CC:	mingo@...e.hu, awalls@...ix.net, linux-kernel@...r.kernel.org,
	jeff@...zik.org, akpm@...ux-foundation.org, rusty@...tcorp.com.au,
	cl@...ux-foundation.org, dhowells@...hat.com,
	arjan@...ux.intel.com, johannes@...solutions.net, oleg@...hat.com,
	axboe@...nel.dk
Subject: Re: Overview of concurrency managed workqueue

Hello,

On 06/15/2010 09:43 PM, Daniel Walker wrote:
> I noticed that you removed the RT workqueue since it's no longer used,
> but it's possible that a user can raise the priority of a given work
> queue thread into real time priorities. So with single threaded, and
> multithreaded workqueues specific to certain areas of the kernel the
> user would have a greater ability to control priorities of those areas.
> 
> It looks like with your patches it would remove that level of
> flexability effectively making all the work item the same priority with
> no ability to raise or lower .. Is that accurate ?

Yes, that is.  With new cmwq, a wq can't assume association with
specific kthread and thus can't use wq as simple frontend to kthreads,
but if somebody wants dedicated kthreads instead of shared ones in
units of work, [s]he should be using kthread.

wq does provide nicer tools for synchronization but in general I don't
think using kthread is too hard and there aren't too many cases
anyway.  If there are many users && kthread is difficult to use
directly, we can definitely write up a wrapping layer tho.  But I
really think using wq as wrapper around kthreads and manipulating
worker thread directly is an abusement.

Thanks.

-- 
tejun
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