On Tue, 05/06 10:32, Fam Zheng wrote:
> On mounted NFS filesystem, ftruncate is much much slower than doing a
> zero write. Changing this significantly speeds up cluster allocation.
>
> Comparing by converting a cirros image (296M) to VMDK on an NFS mount
> point, over 1Gbe LAN:
>
> $ time qemu-img convert cirros-0.3.1.img /mnt/a.raw -O vmdk
>
> Before:
> real 0m26.464s
> user 0m0.133s
> sys 0m0.527s
>
> After:
> real 0m2.120s
> user 0m0.080s
> sys 0m0.197s
>
> Signed-off-by: Fam Zheng <f...@redhat.com>
>
> ---
> V2: Fix cluster_offset check. (Kevin)
>
> Signed-off-by: Fam Zheng <f...@redhat.com>
> ---
> block/vmdk.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/block/vmdk.c b/block/vmdk.c
> index 06a1f9f..98d2d56 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -1037,6 +1037,7 @@ static int get_cluster_offset(BlockDriverState *bs,
> int min_index, i, j;
> uint32_t min_count, *l2_table;
> bool zeroed = false;
> + int64_t ret;
>
> if (m_data) {
> m_data->valid = 0;
> @@ -1110,12 +1111,20 @@ static int get_cluster_offset(BlockDriverState *bs,
> }
>
> /* Avoid the L2 tables update for the images that have snapshots. */
> - *cluster_offset = bdrv_getlength(extent->file);
> + ret = bdrv_getlength(extent->file);
> + if (ret < 0 ||
> + ret & ((extent->cluster_sectors << BDRV_SECTOR_BITS) - 1)) {
> + return VMDK_ERROR;
> + }
> + *cluster_offset = ret;
> if (!extent->compressed) {
> - bdrv_truncate(
> - extent->file,
> - *cluster_offset + (extent->cluster_sectors << 9)
> - );
> + ret = bdrv_write_zeroes(extent->file,
> + *cluster_offset >> BDRV_SECTOR_BITS,
> + extent->cluster_sectors,
> + 0);
Hi Stefan,
By considering a bdrv_write_zeroes as a pre-write, it in general doubles the
write for the whole image, so it's not a good solution.
A better way would be removing the bdrv_truncate and require the caller to do
full cluster write (with a bounce buffer if necessary).
So let's drop this patch.
Thanks,
Fam
