From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53998) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VmRDZ-0004UR-K6 for qemu-devel@nongnu.org; Fri, 29 Nov 2013 11:47:06 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VmRDU-0002w7-Pw for qemu-devel@nongnu.org; Fri, 29 Nov 2013 11:47:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:29207) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VmRDU-0002w1-HD for qemu-devel@nongnu.org; Fri, 29 Nov 2013 11:46:56 -0500 From: Kevin Wolf Date: Fri, 29 Nov 2013 17:45:39 +0100 Message-Id: <1385743555-27888-25-git-send-email-kwolf@redhat.com> In-Reply-To: <1385743555-27888-1-git-send-email-kwolf@redhat.com> References: <1385743555-27888-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PULL 24/41] COW: Speed up writes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws Cc: kwolf@redhat.com, qemu-devel@nongnu.org From: Charlie Shepherd Process a whole sector's worth of COW bits by reading a sector, setting the bits after skipping any already set bits, then writing it out again. Make sure we only flush once before writing metadata, and only if we need to write metadata. Signed-off-by: Charlie Shepherd Signed-off-by: Stefan Hajnoczi --- block/cow.c | 88 +++++++++++++++++++++++++++++++++++-------------------------- 1 file changed, 50 insertions(+), 38 deletions(-) diff --git a/block/cow.c b/block/cow.c index 909c3e7..f759496 100644 --- a/block/cow.c +++ b/block/cow.c @@ -103,40 +103,18 @@ static int cow_open(BlockDriverState *bs, QDict *options, int flags, return ret; } -/* - * 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, bool *first) +static inline void cow_set_bits(uint8_t *bitmap, int start, int64_t nb_sectors) { - uint64_t offset = sizeof(struct cow_header_v2) + bitnum / 8; - uint8_t bitmap; - int ret; - - ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap)); - if (ret < 0) { - return ret; - } - - if (bitmap & (1 << (bitnum % 8))) { - return 0; - } - - if (*first) { - ret = bdrv_flush(bs->file); - if (ret < 0) { - return ret; + int64_t bitnum = start, last = start + nb_sectors; + while (bitnum < last) { + if ((bitnum & 7) == 0 && bitnum + 8 <= last) { + bitmap[bitnum / 8] = 0xFF; + bitnum += 8; + continue; } - *first = false; + bitmap[bitnum/8] |= (1 << (bitnum % 8)); + bitnum++; } - - bitmap |= (1 << (bitnum % 8)); - - ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap)); - if (ret < 0) { - return ret; - } - return 0; } #define BITS_PER_BITMAP_SECTOR (512 * 8) @@ -204,18 +182,52 @@ static int64_t coroutine_fn cow_co_get_block_status(BlockDriverState *bs, static int cow_update_bitmap(BlockDriverState *bs, int64_t sector_num, int nb_sectors) { - int error = 0; - int i; + int64_t bitnum = sector_num + sizeof(struct cow_header_v2) * 8; + uint64_t offset = (bitnum / 8) & -BDRV_SECTOR_SIZE; bool first = true; + int sector_bits; + + for ( ; nb_sectors; + bitnum += sector_bits, + nb_sectors -= sector_bits, + offset += BDRV_SECTOR_SIZE) { + int ret, set; + uint8_t bitmap[BDRV_SECTOR_SIZE]; + + bitnum &= BITS_PER_BITMAP_SECTOR - 1; + sector_bits = MIN(nb_sectors, BITS_PER_BITMAP_SECTOR - bitnum); + + ret = bdrv_pread(bs->file, offset, &bitmap, sizeof(bitmap)); + if (ret < 0) { + return ret; + } + + /* Skip over any already set bits */ + set = cow_find_streak(bitmap, 1, bitnum, sector_bits); + bitnum += set; + sector_bits -= set; + nb_sectors -= set; + if (!sector_bits) { + continue; + } + + if (first) { + ret = bdrv_flush(bs->file); + if (ret < 0) { + return ret; + } + first = false; + } + + cow_set_bits(bitmap, bitnum, sector_bits); - for (i = 0; i < nb_sectors; i++) { - error = cow_set_bit(bs, sector_num + i, &first); - if (error) { - break; + ret = bdrv_pwrite(bs->file, offset, &bitmap, sizeof(bitmap)); + if (ret < 0) { + return ret; } } - return error; + return 0; } static int coroutine_fn cow_read(BlockDriverState *bs, int64_t sector_num, -- 1.8.1.4