From d8c60f4fc2bb0fb0e5b363cd61230e103fbff3ab Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Wed, 4 Dec 2013 17:08:50 +0100 Subject: [PATCH 21/37] block: Make overlap range for serialisation dynamic Message-id: <1392117622-28812-22-git-send-email-kwolf@redhat.com> Patchwork-id: 57186 O-Subject: [RHEL-7.0 qemu-kvm PATCH v2 21/37] block: Make overlap range for serialisation dynamic Bugzilla: 748906 RH-Acked-by: Laszlo Ersek RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Max Reitz Copy on Read wants to serialise with all requests touching the same cluster, so wait_serialising_requests() rounded to cluster boundaries. Other users like alignment RMW will have different requirements, though (requests touching the same sector), so make it dynamic. Signed-off-by: Kevin Wolf Reviewed-by: Max Reitz Reviewed-by: Benoit Canet (cherry picked from commit 7327145f63a224c9ba9c16d0c29781feffef8dc6) Conflicts: include/block/block_int.h Conflicts because in RHEL 7 BdrvTrackedRequest is in block.c Signed-off-by: Kevin Wolf --- block.c | 57 +++++++++++++++++++++++++++++++-------------------------- 1 file changed, 31 insertions(+), 26 deletions(-) --- block.c | 57 +++++++++++++++++++++++++++++++-------------------------- 1 files changed, 31 insertions(+), 26 deletions(-) diff --git a/block.c b/block.c index 7b30bb3..24e94e6 100644 --- a/block.c +++ b/block.c @@ -2039,7 +2039,11 @@ struct BdrvTrackedRequest { int64_t offset; unsigned int bytes; bool is_write; + bool serialising; + int64_t overlap_offset; + unsigned int overlap_bytes; + QLIST_ENTRY(BdrvTrackedRequest) list; Coroutine *co; /* owner, used for deadlock detection */ CoQueue wait_queue; /* coroutines blocked on this request */ @@ -2075,6 +2079,8 @@ static void tracked_request_begin(BdrvTrackedRequest *req, .is_write = is_write, .co = qemu_coroutine_self(), .serialising = false, + .overlap_offset = offset, + .overlap_bytes = bytes, }; qemu_co_queue_init(&req->wait_queue); @@ -2082,12 +2088,19 @@ static void tracked_request_begin(BdrvTrackedRequest *req, QLIST_INSERT_HEAD(&bs->tracked_requests, req, list); } -static void mark_request_serialising(BdrvTrackedRequest *req) +static void mark_request_serialising(BdrvTrackedRequest *req, size_t align) { + int64_t overlap_offset = req->offset & ~(align - 1); + int overlap_bytes = ROUND_UP(req->offset + req->bytes, align) + - overlap_offset; + if (!req->serialising) { req->bs->serialising_in_flight++; req->serialising = true; } + + req->overlap_offset = MIN(req->overlap_offset, overlap_offset); + req->overlap_bytes = MAX(req->overlap_bytes, overlap_bytes); } /** @@ -2111,20 +2124,16 @@ void bdrv_round_to_clusters(BlockDriverState *bs, } } -static void round_bytes_to_clusters(BlockDriverState *bs, - int64_t offset, unsigned int bytes, - int64_t *cluster_offset, - unsigned int *cluster_bytes) +static int bdrv_get_cluster_size(BlockDriverState *bs) { BlockDriverInfo bdi; + int ret; - if (bdrv_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) { - *cluster_offset = offset; - *cluster_bytes = bytes; + ret = bdrv_get_info(bs, &bdi); + if (ret < 0 || bdi.cluster_size == 0) { + return bs->request_alignment; } else { - *cluster_offset = QEMU_ALIGN_DOWN(offset, bdi.cluster_size); - *cluster_bytes = QEMU_ALIGN_UP(offset - *cluster_offset + bytes, - bdi.cluster_size); + return bdi.cluster_size; } } @@ -2132,11 +2141,11 @@ static bool tracked_request_overlaps(BdrvTrackedRequest *req, int64_t offset, unsigned int bytes) { /* aaaa bbbb */ - if (offset >= req->offset + req->bytes) { + if (offset >= req->overlap_offset + req->overlap_bytes) { return false; } /* bbbb aaaa */ - if (req->offset >= offset + bytes) { + if (req->overlap_offset >= offset + bytes) { return false; } return true; @@ -2146,30 +2155,21 @@ static void coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) { BlockDriverState *bs = self->bs; BdrvTrackedRequest *req; - int64_t cluster_offset; - unsigned int cluster_bytes; bool retry; if (!bs->serialising_in_flight) { return; } - /* If we touch the same cluster it counts as an overlap. This guarantees - * that allocating writes will be serialized and not race with each other - * for the same cluster. For example, in copy-on-read it ensures that the - * CoR read and write operations are atomic and guest writes cannot - * interleave between them. - */ - round_bytes_to_clusters(bs, self->offset, self->bytes, - &cluster_offset, &cluster_bytes); - do { retry = false; QLIST_FOREACH(req, &bs->tracked_requests, list) { if (req == self || (!req->serialising && !self->serialising)) { continue; } - if (tracked_request_overlaps(req, cluster_offset, cluster_bytes)) { + if (tracked_request_overlaps(req, self->overlap_offset, + self->overlap_bytes)) + { /* Hitting this means there was a reentrant request, for * example, a block driver issuing nested requests. This must * never happen since it means deadlock. @@ -2780,7 +2780,12 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs, /* Handle Copy on Read and associated serialisation */ if (flags & BDRV_REQ_COPY_ON_READ) { - mark_request_serialising(req); + /* If we touch the same cluster it counts as an overlap. This + * guarantees that allocating writes will be serialized and not race + * with each other for the same cluster. For example, in copy-on-read + * it ensures that the CoR read and write operations are atomic and + * guest writes cannot interleave between them. */ + mark_request_serialising(req, bdrv_get_cluster_size(bs)); } wait_serialising_requests(req); -- 1.7.1