linux-kernel - Re: [RFC PATCHSET] workqueue: implement concurrency managed workqueue

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Message-ID: <4AC5E7BA.5060700@kernel.org>
Date:	Fri, 02 Oct 2009 20:44:58 +0900
From:	Tejun Heo <tj@...nel.org>
To:	David Howells <dhowells@...hat.com>
CC:	jeff@...zik.org, mingo@...e.hu, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	arjan@...ux.intel.com
Subject: Re: [RFC PATCHSET] workqueue: implement concurrency managed workqueue

Hello, David Howells.

David Howells wrote:
> Sounds interesting as a replacement for slow-work.  Some thoughts for you:
> 
> The most important features of slow-work are:
> 
>  (1) Work items are not re-entered whilst they are executing.
> 
>  (2) The slow-work facility keeps references on its work items by asking the
>      client to get and put on the client's refcount.
> 
>  (3) The slow-work facility can create a lot more threads than the number of
>      CPUs on a system, and the system doesn't grind to a halt if they're all
>      taken up with long term I/O (performing several mkdirs for example).
> 
> I think you have (1) and (3) covered, but I'm unsure about (2).

Given that slow-work isn't being used too extensively yet, I was
thinking whether that part could be pushed down to the caller.  Or, we
can also wrap work and export an interface which supports the get/put
reference.

> Also, does it actually make sense to bind threads that are
> performing long-term I/O to particular CPUs?  Threads that are going
> to spend a lot more time sleeping on disk I/O than actually running
> on a CPU?

Binding is usually beneficial and doesn't matter for IO intensive
ones, so...

Thanks.

-- 
tejun
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