Message-ID: <4C18BF40.40607@kernel.org>
Date: Wed, 16 Jun 2010 14:10:40 +0200
From: Tejun Heo <tj@kernel.org>
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To: Daniel Walker <dwalker@codeaurora.org>
CC: mingo@elte.hu, awalls@radix.net, linux-kernel@vger.kernel.org,
       jeff@garzik.org, akpm@linux-foundation.org, rusty@rustcorp.com.au,
       cl@linux-foundation.org, dhowells@redhat.com, arjan@linux.intel.com,
       johannes@sipsolutions.net, oleg@redhat.com, axboe@kernel.dk
Subject: Re: Overview of concurrency managed workqueue
References: <1276551467-21246-1-git-send-email-tj@kernel.org>	 <4C17C598.7070303@kernel.org> <1276631037.6432.9.camel@c-dwalke-linux.qualcomm.com>
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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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