aboutsummaryrefslogtreecommitdiff
path: root/qemu-img.c
diff options
context:
space:
mode:
authorEric Blake <eblake@redhat.com>2017-10-11 22:47:10 -0500
committerKevin Wolf <kwolf@redhat.com>2017-10-26 14:45:57 +0200
commit391cb1aacad155bea4270b863710bba9adabe311 (patch)
treefcb547a220d3dbd1b1ee722cbeff8a70d3a9b0cc /qemu-img.c
parent7daddc615e694ede5dd75366e8a0407f2404ccd8 (diff)
downloadqemu-391cb1aacad155bea4270b863710bba9adabe311.zip
qemu-391cb1aacad155bea4270b863710bba9adabe311.tar.gz
qemu-391cb1aacad155bea4270b863710bba9adabe311.tar.bz2
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.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/qemu-img.c b/qemu-img.c
index cfa28d4..e4b84c4 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);