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qemu-img: use blk_co_pwrite_zeroes for zero sectors when compressed 

When the buffer is zero, blk_co_pwrite_zeroes is more effective than
blk_co_pwritev with BDRV_REQ_WRITE_COMPRESSED. This patch can reduce
the time for converting qcow2 images with lots of zero data.

Signed-off-by: Lidong Chen <lidongchen@tencent.com>
Message-id: 1493261907-18734-1-git-send-email-lidongchen@tencent.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
pull/9/merge
Lidong Chen 9 years ago
committed by Max Reitz
parent
9f1b92add2
commit
db933fbe06
1 changed files with 14 additions and 30 deletions
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  1. 44
      qemu-img.c

44
qemu-img.c
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@ -1649,6 +1649,8 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num,
while (nb_sectors > 0) {
int n = nb_sectors;
BdrvRequestFlags flags = s->compressed ? BDRV_REQ_WRITE_COMPRESSED : 0;
switch (status) {
case BLK_BACKING_FILE:
/* If we have a backing file, leave clusters unallocated that are
@ -1658,43 +1660,24 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num,
break;
case BLK_DATA:
/* We must always write compressed clusters as a whole, so don't
* try to find zeroed parts in the buffer. We can only save the
* write if the buffer is completely zeroed and we're allowed to
* keep the target sparse. */
if (s->compressed) {
if (s->has_zero_init && s->min_sparse &&
buffer_is_zero(buf, n * BDRV_SECTOR_SIZE))
{
assert(!s->target_has_backing);
break;
}
iov.iov_base = buf;
iov.iov_len = n << BDRV_SECTOR_BITS;
qemu_iovec_init_external(&qiov, &iov, 1);
ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,
n << BDRV_SECTOR_BITS, &qiov,
BDRV_REQ_WRITE_COMPRESSED);
if (ret < 0) {
return ret;
}
break;
}
/* If there is real non-zero data or we're told to keep the target
* fully allocated (-S 0), we must write it. Otherwise we can treat
* it as zero sectors. */
/* If we're told to keep the target fully allocated (-S 0) or there
* is real non-zero data, we must write it. Otherwise we can treat
* it as zero sectors.
* Compressed clusters need to be written as a whole, so in that
* case we can only save the write if the buffer is completely
* zeroed. */
if (!s->min_sparse ||
is_allocated_sectors_min(buf, n, &n, s->min_sparse))
(!s->compressed &&
is_allocated_sectors_min(buf, n, &n, s->min_sparse)) ||
(s->compressed &&
!buffer_is_zero(buf, n * BDRV_SECTOR_SIZE)))
{
iov.iov_base = buf;
iov.iov_len = n << BDRV_SECTOR_BITS;
qemu_iovec_init_external(&qiov, &iov, 1);
ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,
n << BDRV_SECTOR_BITS, &qiov, 0);
n << BDRV_SECTOR_BITS, &qiov, flags);
if (ret < 0) {
return ret;
}
@ -1704,6 +1687,7 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num,
case BLK_ZERO:
if (s->has_zero_init) {
assert(!s->target_has_backing);
break;
}
ret = blk_co_pwrite_zeroes(s->target,

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