From ddaa3bc746bdf8974337f176e3841b7c27d7253e Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Tue, 3 Dec 2013 16:34:41 +0100 Subject: [PATCH 24/37] block: Align requests in bdrv_co_do_pwritev() Message-id: <1392117622-28812-25-git-send-email-kwolf@redhat.com> Patchwork-id: 57189 O-Subject: [RHEL-7.0 qemu-kvm PATCH v2 24/37] block: Align requests in bdrv_co_do_pwritev() Bugzilla: 748906 RH-Acked-by: Laszlo Ersek RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Max Reitz 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 Reviewed-by: Max Reitz Reviewed-by: Benoit Canet (cherry picked from commit 3b8242e0ea2a2c201ef3d1bd24080490dae33080) Signed-off-by: Kevin Wolf --- block.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 85 insertions(+), 1 deletion(-) --- block.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 files changed, 85 insertions(+), 1 deletions(-) diff --git a/block.c b/block.c index fd37037..3ec3949 100644 --- a/block.c +++ b/block.c @@ -3078,6 +3078,12 @@ 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) { @@ -3096,10 +3102,88 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs, bdrv_io_limits_intercept(bs, true, bytes >> BDRV_SECTOR_BITS); } + /* + * 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; } -- 1.7.1