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cow: make writes go at a less indecent speed

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Only sync once per write, rather than once per sector.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Paolo Bonzini 2013-09-04 19:00:19 +02:00 committed by Stefan Hajnoczi
parent 276cbc7f2f
commit 26ae980492
1 changed files with 16 additions and 3 deletions
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19
block/cow.c
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@ -106,7 +106,7 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags)
* XXX(hch): right now these functions are extremely inefficient. * XXX(hch): right now these functions are extremely inefficient.
* We should just read the whole bitmap we'll need in one go instead. * We should just read the whole bitmap we'll need in one go instead.
*/ */
static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum) static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum, bool *first)
{ {
uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8; uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8;
uint8_t bitmap; uint8_t bitmap;
@ -117,9 +117,21 @@ static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum)
return ret; return ret;
} }
if (bitmap & (1 << (bitnum % 8))) {
return 0;
}
if (*first) {
ret = bdrv_flush(bs->file);
if (ret < 0) {
return ret;
}
*first = false;
}
bitmap |= (1 << (bitnum % 8)); bitmap |= (1 << (bitnum % 8));
ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap)); ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap));
if (ret < 0) { if (ret < 0) {
return ret; return ret;
} }
@ -181,9 +193,10 @@ static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num,
{ {
int error = 0; int error = 0;
int i; int i;
bool first = true;
for (i = 0; i < nb_sectors; i++) { for (i = 0; i < nb_sectors; i++) {
error = cow_set_bit(bs, sector_num + i); error = cow_set_bit(bs, sector_num + i, &first);
if (error) { if (error) {
break; break;
} }