Re: [PATCH 0/9] kvm tools, qcow: Improve QCOW performance

Ingo Molnar
2011-07-10T17:15:53Z

* Pekka Enberg <penberg@kernel.org> wrote:

> This series fixes QCOW locking issues and implements delayed metadata writeout.
> This improves performance of writeout to QCOW2 images that don't have clusters
> and L2 tables allocated on-disk.
>
> I tested the series by running
>
> mount -t ext4 /dev/vdb /mnt
> dd if=/dev/zero of=/mnt/tmp
>
> in the guest multiple times for fresly generated QCOW2 image:
>
> dd if=/dev/zero of=fs.ext4 bs=1024k count=512 && mkfs.ext4 -F fs.ext4 && qemu-img convert -O qcow2 fs.ext4 fs.qcow2
>
> which causes worst-case behavior for the current code.
>
> Before:
>
> [ seekwatcher: http://userweb.kernel.org/~penberg/kvm-qcow-delayed/kvm-qcow2-master.png ]
>
> 511229952 bytes (511 MB) copied, 19.906 s, 25.7 MB/s
> 511229952 bytes (511 MB) copied, 20.3168 s, 25.2 MB/s
> 511229952 bytes (511 MB) copied, 20.8078 s, 24.6 MB/s
> 511229952 bytes (511 MB) copied, 21.0889 s, 24.2 MB/s
> 511229952 bytes (511 MB) copied, 20.7833 s, 24.6 MB/s
> 511229952 bytes (511 MB) copied, 20.7536 s, 24.6 MB/s
> 511229952 bytes (511 MB) copied, 20.0312 s, 25.5 MB/s
>
> After:
>
> [ seekwatcher: http://userweb.kernel.org/~penberg/kvm-qcow-delayed/kvm-qcow2-delayed.png ]
>
> 511229952 bytes (511 MB) copied, 7.68312 s, 66.5 MB/s
> 511229952 bytes (511 MB) copied, 7.54065 s, 67.8 MB/s
> 511229952 bytes (511 MB) copied, 9.34749 s, 54.7 MB/s
> 511229952 bytes (511 MB) copied, 9.2421 s, 55.3 MB/s
> 511229952 bytes (511 MB) copied, 9.9364 s, 51.5 MB/s
> 511229952 bytes (511 MB) copied, 10.0337 s, 51.0 MB/s
> 511229952 bytes (511 MB) copied, 9.39502 s, 54.4 MB/s

Just wondering, how does Qemu perform on the same system using the
same image, with comparable settings?

Thanks,

Ingo