From a1a7f1301c20582d3326e33acd94a4c198c60bcd Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 18 Oct 2013 08:14:27 +0200 Subject: [PATCH 02/81] cow: make writes go at a less indecent speed RH-Author: Paolo Bonzini Message-id: <1382084091-16636-3-git-send-email-pbonzini@redhat.com> Patchwork-id: 54985 O-Subject: [RHEL 7.0 qemu-kvm PATCH 02/26] cow: make writes go at a less indecent speed Bugzilla: 989646 RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Max Reitz RH-Acked-by: Kevin Wolf Only sync once per write, rather than once per sector. Reviewed-by: Eric Blake Signed-off-by: Paolo Bonzini (cherry picked from commit 26ae980492920e417bc91761cc85950f18e41f85) --- block/cow.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) Signed-off-by: Miroslav Rezanina --- block/cow.c | 19 ++++++++++++++++--- 1 files changed, 16 insertions(+), 3 deletions(-) diff --git a/block/cow.c b/block/cow.c index c12088b..2f72334 100644 --- a/block/cow.c +++ b/block/cow.c @@ -106,7 +106,7 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags) * XXX(hch): right now these functions are extremely inefficient. * 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; uint8_t bitmap; @@ -117,9 +117,21 @@ static inline int cow_set_bit(BlockDriverState *bs, int64_t bitnum) 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)); - ret = bdrv_pwrite_sync(bs->file, offset, &bitmap, sizeof(bitmap)); + ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap)); if (ret < 0) { return ret; } @@ -181,9 +193,10 @@ static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num, { int error = 0; int i; + bool first = true; 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) { break; } -- 1.7.1