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block: Align requests in bdrv_co_do_pwritev() 

This patch changes bdrv_co_do_pwritev() to actually be what its name
promises. If requests aren't properly aligned, it performs a RMW.

Requests touching the same block are serialised against the RMW request.
Further optimisation of this is possible by differentiating types of
requests (concurrent reads should actually be okay here).

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
This commit is contained in:
Kevin Wolf 2013-12-03 16:34:41 +01:00
parent 6460440f34
commit 3b8242e0ea
1 changed files with 85 additions and 1 deletions
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86
block.c
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@ -3235,6 +3235,12 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
BdrvRequestFlags flags)
{
BdrvTrackedRequest req;
/* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
uint8_t *head_buf = NULL;
uint8_t *tail_buf = NULL;
QEMUIOVector local_qiov;
bool use_local_qiov = false;
int ret;
if (!bs->drv) {
@ -3253,10 +3259,88 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
bdrv_io_limits_intercept(bs, bytes >> BDRV_SECTOR_BITS, true);
}
/*
* Align write if necessary by performing a read-modify-write cycle.
* Pad qiov with the read parts and be sure to have a tracked request not
* only for bdrv_aligned_pwritev, but also for the reads of the RMW cycle.
*/
tracked_request_begin(&req, bs, offset, bytes, true);
ret = bdrv_aligned_pwritev(bs, &req, offset, bytes, qiov, flags);
if (offset & (align - 1)) {
QEMUIOVector head_qiov;
struct iovec head_iov;
mark_request_serialising(&req, align);
wait_serialising_requests(&req);
head_buf = qemu_blockalign(bs, align);
head_iov = (struct iovec) {
.iov_base = head_buf,
.iov_len = align,
};
qemu_iovec_init_external(&head_qiov, &head_iov, 1);
ret = bdrv_aligned_preadv(bs, &req, offset & ~(align - 1), align,
align, &head_qiov, 0);
if (ret < 0) {
goto fail;
}
qemu_iovec_init(&local_qiov, qiov->niov + 2);
qemu_iovec_add(&local_qiov, head_buf, offset & (align - 1));
qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size);
use_local_qiov = true;
bytes += offset & (align - 1);
offset = offset & ~(align - 1);
}
if ((offset + bytes) & (align - 1)) {
QEMUIOVector tail_qiov;
struct iovec tail_iov;
size_t tail_bytes;
mark_request_serialising(&req, align);
wait_serialising_requests(&req);
tail_buf = qemu_blockalign(bs, align);
tail_iov = (struct iovec) {
.iov_base = tail_buf,
.iov_len = align,
};
qemu_iovec_init_external(&tail_qiov, &tail_iov, 1);
ret = bdrv_aligned_preadv(bs, &req, (offset + bytes) & ~(align - 1), align,
align, &tail_qiov, 0);
if (ret < 0) {
goto fail;
}
if (!use_local_qiov) {
qemu_iovec_init(&local_qiov, qiov->niov + 1);
qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size);
use_local_qiov = true;
}
tail_bytes = (offset + bytes) & (align - 1);
qemu_iovec_add(&local_qiov, tail_buf + tail_bytes, align - tail_bytes);
bytes = ROUND_UP(bytes, align);
}
ret = bdrv_aligned_pwritev(bs, &req, offset, bytes,
use_local_qiov ? &local_qiov : qiov,
flags);
fail:
tracked_request_end(&req);
if (use_local_qiov) {
qemu_iovec_destroy(&local_qiov);
qemu_vfree(head_buf);
qemu_vfree(tail_buf);
}
return ret;
}