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[PATCH v2 2/3] block/io: align requests to subcluster_size
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From: |
Andrey Drobyshev |
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Subject: |
[PATCH v2 2/3] block/io: align requests to subcluster_size |
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Date: |
Tue, 11 Jul 2023 20:25:52 +0300 |
When target image is using subclusters, and we align the request during
copy-on-read, it makes sense to align to subcluster_size rather than
cluster_size. Otherwise we end up with unnecessary allocations.
This commit renames bdrv_round_to_clusters() to bdrv_round_to_subclusters()
and utilizes subcluster_size field of BlockDriverInfo to make necessary
alignments. It affects copy-on-read as well as mirror job (which is
using bdrv_round_to_clusters()).
This change also fixes the following bug with failing assert (covered by
the test in the subsequent commit):
qemu-img create -f qcow2 base.qcow2 64K
qemu-img create -f qcow2 -o
extended_l2=on,backing_file=base.qcow2,backing_fmt=qcow2 img.qcow2 64K
qemu-io -c "write -P 0xaa 0 2K" img.qcow2
qemu-io -C -c "read -P 0x00 2K 62K" img.qcow2
qemu-io: ../block/io.c:1236: bdrv_co_do_copy_on_readv: Assertion `skip_bytes <
pnum' failed.
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
block/io.c | 50 ++++++++++++++++++++--------------------
block/mirror.c | 8 +++----
include/block/block-io.h | 8 +++----
3 files changed, 33 insertions(+), 33 deletions(-)
diff --git a/block/io.c b/block/io.c
index e8293d6b26..4a2fef6a77 100644
--- a/block/io.c
+++ b/block/io.c
@@ -728,21 +728,21 @@ BdrvTrackedRequest *coroutine_fn
bdrv_co_get_self_request(BlockDriverState *bs)
}
/**
- * Round a region to cluster boundaries
+ * Round a region to subcluster (if supported) or cluster boundaries
*/
void coroutine_fn GRAPH_RDLOCK
-bdrv_round_to_clusters(BlockDriverState *bs, int64_t offset, int64_t bytes,
- int64_t *cluster_offset, int64_t *cluster_bytes)
+bdrv_round_to_subclusters(BlockDriverState *bs, int64_t offset, int64_t bytes,
+ int64_t *align_offset, int64_t *align_bytes)
{
BlockDriverInfo bdi;
IO_CODE();
- if (bdrv_co_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) {
- *cluster_offset = offset;
- *cluster_bytes = bytes;
+ if (bdrv_co_get_info(bs, &bdi) < 0 || bdi.subcluster_size == 0) {
+ *align_offset = offset;
+ *align_bytes = bytes;
} else {
- int64_t c = bdi.cluster_size;
- *cluster_offset = QEMU_ALIGN_DOWN(offset, c);
- *cluster_bytes = QEMU_ALIGN_UP(offset - *cluster_offset + bytes, c);
+ int64_t c = bdi.subcluster_size;
+ *align_offset = QEMU_ALIGN_DOWN(offset, c);
+ *align_bytes = QEMU_ALIGN_UP(offset - *align_offset + bytes, c);
}
}
@@ -1168,8 +1168,8 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t
offset, int64_t bytes,
void *bounce_buffer = NULL;
BlockDriver *drv = bs->drv;
- int64_t cluster_offset;
- int64_t cluster_bytes;
+ int64_t align_offset;
+ int64_t align_bytes;
int64_t skip_bytes;
int ret;
int max_transfer = MIN_NON_ZERO(bs->bl.max_transfer,
@@ -1203,28 +1203,28 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t
offset, int64_t bytes,
* BDRV_REQUEST_MAX_BYTES (even when the original read did not), which
* is one reason we loop rather than doing it all at once.
*/
- bdrv_round_to_clusters(bs, offset, bytes, &cluster_offset, &cluster_bytes);
- skip_bytes = offset - cluster_offset;
+ bdrv_round_to_subclusters(bs, offset, bytes, &align_offset, &align_bytes);
+ skip_bytes = offset - align_offset;
trace_bdrv_co_do_copy_on_readv(bs, offset, bytes,
- cluster_offset, cluster_bytes);
+ align_offset, align_bytes);
- while (cluster_bytes) {
+ while (align_bytes) {
int64_t pnum;
if (skip_write) {
ret = 1; /* "already allocated", so nothing will be copied */
- pnum = MIN(cluster_bytes, max_transfer);
+ pnum = MIN(align_bytes, max_transfer);
} else {
- ret = bdrv_is_allocated(bs, cluster_offset,
- MIN(cluster_bytes, max_transfer), &pnum);
+ ret = bdrv_is_allocated(bs, align_offset,
+ MIN(align_bytes, max_transfer), &pnum);
if (ret < 0) {
/*
* Safe to treat errors in querying allocation as if
* unallocated; we'll probably fail again soon on the
* read, but at least that will set a decent errno.
*/
- pnum = MIN(cluster_bytes, max_transfer);
+ pnum = MIN(align_bytes, max_transfer);
}
/* Stop at EOF if the image ends in the middle of the cluster */
@@ -1242,7 +1242,7 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t
offset, int64_t bytes,
/* Must copy-on-read; use the bounce buffer */
pnum = MIN(pnum, MAX_BOUNCE_BUFFER);
if (!bounce_buffer) {
- int64_t max_we_need = MAX(pnum, cluster_bytes - pnum);
+ int64_t max_we_need = MAX(pnum, align_bytes - pnum);
int64_t max_allowed = MIN(max_transfer, MAX_BOUNCE_BUFFER);
int64_t bounce_buffer_len = MIN(max_we_need, max_allowed);
@@ -1254,7 +1254,7 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t
offset, int64_t bytes,
}
qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);
- ret = bdrv_driver_preadv(bs, cluster_offset, pnum,
+ ret = bdrv_driver_preadv(bs, align_offset, pnum,
&local_qiov, 0, 0);
if (ret < 0) {
goto err;
@@ -1266,13 +1266,13 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t
offset, int64_t bytes,
/* FIXME: Should we (perhaps conditionally) be setting
* BDRV_REQ_MAY_UNMAP, if it will allow for a sparser copy
* that still correctly reads as zero? */
- ret = bdrv_co_do_pwrite_zeroes(bs, cluster_offset, pnum,
+ ret = bdrv_co_do_pwrite_zeroes(bs, align_offset, pnum,
BDRV_REQ_WRITE_UNCHANGED);
} else {
/* This does not change the data on the disk, it is not
* necessary to flush even in cache=writethrough mode.
*/
- ret = bdrv_driver_pwritev(bs, cluster_offset, pnum,
+ ret = bdrv_driver_pwritev(bs, align_offset, pnum,
&local_qiov, 0,
BDRV_REQ_WRITE_UNCHANGED);
}
@@ -1301,8 +1301,8 @@ bdrv_co_do_copy_on_readv(BdrvChild *child, int64_t
offset, int64_t bytes,
}
}
- cluster_offset += pnum;
- cluster_bytes -= pnum;
+ align_offset += pnum;
+ align_bytes -= pnum;
progress += pnum - skip_bytes;
skip_bytes = 0;
}
diff --git a/block/mirror.c b/block/mirror.c
index d3cacd1708..e213a892db 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -283,8 +283,8 @@ static int coroutine_fn mirror_cow_align(MirrorBlockJob *s,
int64_t *offset,
need_cow |= !test_bit((*offset + *bytes - 1) / s->granularity,
s->cow_bitmap);
if (need_cow) {
- bdrv_round_to_clusters(blk_bs(s->target), *offset, *bytes,
- &align_offset, &align_bytes);
+ bdrv_round_to_subclusters(blk_bs(s->target), *offset, *bytes,
+ &align_offset, &align_bytes);
}
if (align_bytes > max_bytes) {
@@ -576,8 +576,8 @@ static void coroutine_fn mirror_iteration(MirrorBlockJob *s)
int64_t target_offset;
int64_t target_bytes;
WITH_GRAPH_RDLOCK_GUARD() {
- bdrv_round_to_clusters(blk_bs(s->target), offset, io_bytes,
- &target_offset, &target_bytes);
+ bdrv_round_to_subclusters(blk_bs(s->target), offset, io_bytes,
+ &target_offset, &target_bytes);
}
if (target_offset == offset &&
target_bytes == io_bytes) {
diff --git a/include/block/block-io.h b/include/block/block-io.h
index 4415506e40..6db48f2d35 100644
--- a/include/block/block-io.h
+++ b/include/block/block-io.h
@@ -189,10 +189,10 @@ bdrv_get_info(BlockDriverState *bs, BlockDriverInfo *bdi);
ImageInfoSpecific *bdrv_get_specific_info(BlockDriverState *bs,
Error **errp);
BlockStatsSpecific *bdrv_get_specific_stats(BlockDriverState *bs);
-void bdrv_round_to_clusters(BlockDriverState *bs,
- int64_t offset, int64_t bytes,
- int64_t *cluster_offset,
- int64_t *cluster_bytes);
+void bdrv_round_to_subclusters(BlockDriverState *bs,
+ int64_t offset, int64_t bytes,
+ int64_t *cluster_offset,
+ int64_t *cluster_bytes);
void bdrv_get_backing_filename(BlockDriverState *bs,
char *filename, int filename_size);
--
2.39.3