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[Qemu-devel] [PATCH 19/22] block: Align requests in bdrv_co_do_pwritev()
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH 19/22] block: Align requests in bdrv_co_do_pwritev() |
Date: |
Wed, 11 Dec 2013 22:08:26 +0100 |
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 <address@hidden>
---
block.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 85 insertions(+), 1 deletion(-)
diff --git a/block.c b/block.c
index 6630b41..98ea723 100644
--- a/block.c
+++ b/block.c
@@ -3039,6 +3039,12 @@ 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) {
@@ -3056,10 +3062,88 @@ 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;
}
--
1.8.1.4
- Re: [Qemu-devel] [PATCH 07/22] block: rename buffer_alignment to guest_block_size, (continued)
- [Qemu-devel] [PATCH 10/22] block: Introduce bdrv_co_do_preadv(), Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 11/22] block: Introduce bdrv_aligned_pwritev(), Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 12/22] block: write: Handle COR dependency after I/O throttling, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 13/22] block: Introduce bdrv_co_do_pwritev(), Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 14/22] block: Switch BdrvTrackedRequest to byte granularity, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 16/22] block: Make zero-after-EOF work with larger alignment, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 15/22] block: Allow waiting for overlapping requests between begin/end, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 17/22] block: Generalise and optimise COR serialisation, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 18/22] block: Make overlap range for serialisation dynamic, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 19/22] block: Align requests in bdrv_co_do_pwritev(),
Kevin Wolf <=
- [Qemu-devel] [PATCH 20/22] block: Change coroutine wrapper to byte granularity, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 21/22] block: Make bdrv_pread() a bdrv_prwv_co() wrapper, Kevin Wolf, 2013/12/11
- [Qemu-devel] [PATCH 22/22] block: Make bdrv_pwrite() a bdrv_prwv_co() wrapper, Kevin Wolf, 2013/12/11
- Re: [Qemu-devel] [PATCH 00/22] block: Support for 512b-on-4k emulation, Peter Lieven, 2013/12/12