Re: [Qemu-devel] [PATCH 26/27] block/parallels: optimize linear image expansion

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Apr 28, 2015 at 10:46:59AM +0300, Denis V. Lunev wrote:
> Plain image expansion spends a lot of time to update image file size.
> This seriously affects the performance. The following simple test
>   qemu_img create -f parallels -o cluster_size=64k ./1.hds 64G
>   qemu_io -n -c "write -P 0x11 0 1024M" ./1.hds
> could be improved if the format driver will pre-allocate some space
> in the image file with a reasonable chunk.
> 
> This patch preallocates 128 Mb using bdrv_write_zeroes, which should
> normally use fallocate() call inside. Fallback to older truncate()
> could be used as a fallback using image open options thanks to the
> previous patch.
> 
> The benefit is around 15%.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Reviewed-by: Roman Karan <rkagan@parallels.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/parallels.c | 42 ++++++++++++++++++++++++++++++++----------
>  1 file changed, 32 insertions(+), 10 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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