Re: [Qemu-devel] [PATCH 19/19] block/parallels: optimize linear image expansion

[Roman Kagan]

On Tue, Dec 30, 2014 at 01:07:12PM +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%.
> 
> This patch is final in this series. Block driver has near native
> performance now.
> 
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> ---
>  block/parallels.c | 35 +++++++++++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)
> 
> diff --git a/block/parallels.c b/block/parallels.c
> index 12a9cea..5ec4a0d 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -82,6 +82,7 @@ typedef struct BDRVParallelsState {
>      int bat_cache_off;
>      int data_off;
>  
> +    int64_t  prealloc_off;

This field name confused me.  I think "data_end" would fit better.

Otherwise looks good to me.

Roman.