[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PULL 24/41] COW: Speed up writes
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PULL 24/41] COW: Speed up writes |
Date: |
Fri, 29 Nov 2013 17:45:39 +0100 |
From: Charlie Shepherd <address@hidden>
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 <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
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
- [Qemu-devel] [PULL 13/41] iscsi: add bdrv_co_write_zeroes, (continued)
- [Qemu-devel] [PULL 13/41] iscsi: add bdrv_co_write_zeroes, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 14/41] block: introduce bdrv_make_zero, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 15/41] block/get_block_status: fix BDRV_BLOCK_ZERO for unallocated blocks, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 16/41] qemu-img: add support for fully allocated images, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 17/41] qemu-img: conditionally zero out target on convert, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 18/41] util/error: Save errno from clobbering, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 19/41] Test coroutine execution order, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 20/41] sheepdog: implement .bdrv_get_allocated_file_size, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 21/41] block/stream: Don't stream unbacked devices, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 22/41] block: per caller dirty bitmap, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 24/41] COW: Speed up writes,
Kevin Wolf <=
- [Qemu-devel] [PULL 25/41] COW: Extend checking allocated bits to beyond one sector, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 26/41] MAINTAINERS: add sheepdog development mailing list, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 23/41] qapi: Change BlockDirtyInfo to list, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 27/41] qdict: Fix memory leak in qdict_do_flatten(), Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 28/41] qdict: Optimise qdict_do_flatten(), Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 29/41] sheepdog: refactor do_sd_create(), Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 31/41] qemu-iotests: Drop local version of cancel_and_wait from 040, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 30/41] sheepdog: support user-defined redundancy option, Kevin Wolf, 2013/11/29
- [Qemu-devel] [PULL 32/41] blkdebug: add "remove_break" command, Kevin Wolf, 2013/11/29