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

["Denis V. Lunev" <den@openvz.org>]

On 14/01/15 20:56, Roman Kagan wrote:
> 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 <den@openvz.org>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> CC: Stefan Hajnoczi <stefanha@redhat.com>
>> ---
>>   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.
agree