Re: [Qemu-devel] [PATCH v3 20/29] block: Align requests in bdrv_co_do_pwritev()
Le Friday 17 Jan 2014 à 15:15:10 (+0100), Kevin Wolf a écrit :
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 kw...@redhat.com
Reviewed-by: Max Reitz mre...@redhat.com
---
block.c | 86
-
1 file changed, 85 insertions(+), 1 deletion(-)
diff --git a/block.c b/block.c
index 55e8c69..859e1aa 100644
--- a/block.c
+++ b/block.c
@@ -3055,6 +3055,12 @@ 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) {
@@ -3073,10 +3079,88 @@ 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
Reviewed-by: Benoit Canet ben...@irqsave.net
[Qemu-devel] [PATCH v3 20/29] 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 kw...@redhat.com
Reviewed-by: Max Reitz mre...@redhat.com
---
block.c | 86 -
1 file changed, 85 insertions(+), 1 deletion(-)
diff --git a/block.c b/block.c
index 55e8c69..859e1aa 100644
--- a/block.c
+++ b/block.c
@@ -3055,6 +3055,12 @@ 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) {
@@ -3073,10 +3079,88 @@ 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
