linux-kernel - Re: [PATCHSET] backing-dev: replace private thread pool with workqueue

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Date:	Sat, 27 Nov 2010 19:50:28 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Christoph Hellwig <hch@....de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHSET] backing-dev: replace private thread pool with   workqueue

On 2010-11-27 17:02, Tejun Heo wrote:
> On 09/07/2010 02:36 PM, Tejun Heo wrote:
>> Hello,
>>
>> On 09/07/2010 02:29 PM, Jens Axboe wrote:
>>> I agree (with both of you). It's definitely too early to convert it
>>> over, but if we can in the longer run, it never hurts to get rid of
>>> code. The writeback threads aren't a typical threadpool, in that the
>>> threads stick around and only go away when idle for too long. If they
>>> stick around, you get the same process hammering IO at your device. So
>>> converting that over to the generic cwq may or may not be at a
>>> performance cost, it'll definitely have to be tested.
>>
>> One thing to try is removing WQ_UNBOUND and see how it affects the
>> performance.  I put WQ_UNBOUND there mainly to keep the behavior about
>> the same as the current code but given what it does I think it would
>> probably fare better with workers bound to CPUs.
> 
> cmwq now seems pretty solid.  There hasn't been any noticeable failure
> yet.  I think we can move on with this conversion now.  Shall I
> refresh the patchset against the current block tree?

I'd still prefer to wait a while. The writeback code is still very much
a moving target, so I don't think mixing in a different work queue
scheme is likely going to do anyone any good at this point in time.

-- 
Jens Axboe

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