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

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Message-ID: <9942.1254401629@redhat.com>
Date:	Thu, 01 Oct 2009 13:53:49 +0100
From:	David Howells <dhowells@...hat.com>
To:	Tejun Heo <tj@...nel.org>
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,
	dhowells@...hat.com, arjan@...ux.intel.com
Subject: Re: [RFC PATCHSET] workqueue: implement concurrency managed workqueue


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).

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?

David
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