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

[Laurent Vivier <Laurent.Vivier@bull.net>]

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.

My test process was:

qemu-img create test.qcow2 500MB
qemu ... -hda boot.raw -hdb test.qcow2

mkfs /dev/hdb
fsck /dev/hdb
mount /dev/hdb /mnt
cd /mnt
dbench 16
cd
umount /mnt
fsck /dev/hdb
mkfs /dev/hdb
fsck /dev/hdb
mount /dev/hdb /mnt
cd /mnt
tar xvf /root/linux.tar.bz2
cd
umount /mnt
fsck /dev/hdb
mount /mnt
cd /mnt/linux/
make defconfig
make
cd
umount /mnt
fsck /dev/hdb
mount /mnt
cd /mnt/linux
make clean
cd
umount /mnt
fsck /dev/hdb
mount /dev/hdb
cd /mnt
rm -fr linux
cd 
umount /mnt
fsck /dev/hdb
mkfs /dev/hdb
fsck /dev/hdb
mount /dev/hdb /mnt
dd if=/dev/zero of=/mnt/file
umount /mnt
fsck /dev/hdb
mount /dev/hdb /mnt
rm /mnt/file
umount /mnt
fsck /dev/hdb
mount /dev/hdb /mnt
cd /mnt
dbench 1
cd
umount /mnt
fsck /dev/hdb

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.

Regards,
Laurent
-- 
----------------- Laurent.Vivier@bull.net  ------------------
  "La perfection est atteinte non quand il ne reste rien à
ajouter mais quand il ne reste rien à enlever." Saint Exupéry