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Re: [Qemu-devel] [patch 0/5][v2] qcow2: improve I/O performance with cac

From: Anthony Liguori
Subject: Re: [Qemu-devel] [patch 0/5][v2] qcow2: improve I/O performance with cache=off
Date: Tue, 29 Jul 2008 16:49:44 -0500
User-agent: Thunderbird (X11/20080501)

Laurent Vivier wrote:
Le mardi 29 juillet 2008 à 14:15 -0500, Anthony Liguori a écrit :
Laurent Vivier wrote:
These patches improve qcow2 performance when used with cache=off.

They modify block-qcow2.c to read/write as many clusters as
possible per bdrv_aio_[read|write]().
This patch series looks like a pretty good clean up of the code. The perf improvement is a nice side effect too.

I'm a little concerned about how much code this touches though. How

Yes, I know, it's why I split it in several patches: easier to review,
easier to test.

much testing have you done of these changes? Have you tested all of the corner cases (backing files, filling up a disk image, etc.)?

Well, before all I made a lot of review of my modifications, but it must
also be reviewed by other eyes.

I think it covers a lot of cases, but I didn't test encrypted disk image
and compressed disk image. The case with backed files was tested only
with mkfs/fsck/dbench.

If you think these patches are good candidates to be included, I can
make more tests.

Yes, I do think these patches make sense. I would like to see more testing though. It all seemed pretty clear to me (breaking out the patches was very helpful!) but I am very worried about corrupting qcow2 images.


Anthony Liguori


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