diff options
| author | Eric Blake <eblake@redhat.com> | 2017-10-11 22:47:10 -0500 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2017-10-26 14:45:57 +0200 |
| commit | 391cb1aacad155bea4270b863710bba9adabe311 (patch) | |
| tree | fcb547a220d3dbd1b1ee722cbeff8a70d3a9b0cc /qemu-img.c | |
| parent | 7daddc615e694ede5dd75366e8a0407f2404ccd8 (diff) | |
qemu-img: Speed up compare on pre-allocated larger file
Compare the following images with all-zero contents:
$ truncate --size 1M A
$ qemu-img create -f qcow2 -o preallocation=off B 1G
$ qemu-img create -f qcow2 -o preallocation=metadata C 1G
On my machine, the difference is noticeable for pre-patch speeds,
with more than an order of magnitude in difference caused by the
choice of preallocation in the qcow2 file:
$ time ./qemu-img compare -f raw -F qcow2 A B
Warning: Image size mismatch!
Images are identical.
real 0m0.014s
user 0m0.007s
sys 0m0.007s
$ time ./qemu-img compare -f raw -F qcow2 A C
Warning: Image size mismatch!
Images are identical.
real 0m0.341s
user 0m0.144s
sys 0m0.188s
Why? Because bdrv_is_allocated() returns false for image B but
true for image C, throwing away the fact that both images know
via lseek(SEEK_HOLE) that the entire image still reads as zero.
From there, qemu-img ends up calling bdrv_pread() for every byte
of the tail, instead of quickly looking for the next allocation.
The solution: use block_status instead of is_allocated, giving:
$ time ./qemu-img compare -f raw -F qcow2 A C
Warning: Image size mismatch!
Images are identical.
real 0m0.014s
user 0m0.011s
sys 0m0.003s
which is on par with the speeds for no pre-allocation.
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qemu-img.c')
| -rw-r--r-- | qemu-img.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/qemu-img.c b/qemu-img.c index cfa28d41d5..e4b84c4f56 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1480,11 +1480,11 @@ static int img_compare(int argc, char **argv) while (sector_num < progress_base) { int64_t count; - ret = bdrv_is_allocated_above(blk_bs(blk_over), NULL, + ret = bdrv_block_status_above(blk_bs(blk_over), NULL, sector_num * BDRV_SECTOR_SIZE, (progress_base - sector_num) * BDRV_SECTOR_SIZE, - &count); + &count, NULL, NULL); if (ret < 0) { ret = 3; error_report("Sector allocation test failed for %s", @@ -1492,11 +1492,11 @@ static int img_compare(int argc, char **argv) goto out; } - /* TODO relax this once bdrv_is_allocated_above does not enforce + /* TODO relax this once bdrv_block_status_above does not enforce * sector alignment */ assert(QEMU_IS_ALIGNED(count, BDRV_SECTOR_SIZE)); nb_sectors = count >> BDRV_SECTOR_BITS; - if (ret) { + if (ret & BDRV_BLOCK_ALLOCATED && !(ret & BDRV_BLOCK_ZERO)) { nb_sectors = MIN(nb_sectors, IO_BUF_SIZE >> BDRV_SECTOR_BITS); ret = check_empty_sectors(blk_over, sector_num, nb_sectors, filename_over, buf1, quiet); |