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Re: [Xen-devel] poor domU VBD performance.

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] poor domU VBD performance.
From: Andrew Theurer <habanero@xxxxxxxxxx>
Date: Thu, 31 Mar 2005 10:02:07 -0600
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, Philip R Auld <pauld@xxxxxxxxxxx>, Kurt Garloff <garloff@xxxxxxx>, Xen development list <xen-devel@xxxxxxxxxxxxxxxxxxx>, Vincent Hanquez <tab@xxxxxxxxx>, Jens Axboe <axboe@xxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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Keir Fraser wrote:


On 31 Mar 2005, at 16:39, Jens Axboe wrote:

Not necessarily - either your io rate is not fast enough to sustain a
substantial queue depth, in that case you get plugging on basically
every io anyways. If on the other hand the io rate is high enough to
maintain a queue depth of > 1, then the plugging will never take place
because the queue never empties.

So all in all, I don't think the temporary work-around will be such a
bad idea. I would still rather implement the queue tracking though, it
should not be more than a few lines of code.


I've checked in something along the lines of what you described into both the 2.0-testing and the unstable trees. Looks to have identical performance to the original simple patch, at least for a bulk 'dd'.

I'll do a pull of unstable and see what I get with o_direct, thanks.

-Andrew


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