From 05d5e12b243df43a8a58568edf6a342806879d98 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 24 Jun 2021 09:20:40 +0200 Subject: [PATCH] block-copy: streamline choice of copy_range vs. read/write Put the logic to determine the copy size in a separate function, so that there is a simple state machine for the possible methods of copying data from one BlockDriverState to the other. Use .method instead of .copy_range as in-out argument, and include also .zeroes as an additional copy method. While at it, store the common computation of block_copy_max_transfer into a new field of BlockCopyState, and make sure that we always obey max_transfer; that's more efficient even for the COPY_RANGE_READ_WRITE case. Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Emanuele Giuseppe Esposito Signed-off-by: Paolo Bonzini Message-Id: <20210624072043.180494-3-eesposit@redhat.com> Signed-off-by: Vladimir Sementsov-Ogievskiy --- block/block-copy.c | 188 +++++++++++++++++++++++---------------------- 1 file changed, 96 insertions(+), 92 deletions(-) diff --git a/block/block-copy.c b/block/block-copy.c index a437978e35..0a1cf3d0cb 100644 --- a/block/block-copy.c +++ b/block/block-copy.c @@ -28,6 +28,14 @@ #define BLOCK_COPY_MAX_WORKERS 64 #define BLOCK_COPY_SLICE_TIME 100000000ULL /* ns */ +typedef enum { + COPY_READ_WRITE_CLUSTER, + COPY_READ_WRITE, + COPY_WRITE_ZEROES, + COPY_RANGE_SMALL, + COPY_RANGE_FULL +} BlockCopyMethod; + static coroutine_fn int block_copy_task_entry(AioTask *task); typedef struct BlockCopyCallState { @@ -64,8 +72,7 @@ typedef struct BlockCopyTask { BlockCopyCallState *call_state; int64_t offset; int64_t bytes; - bool zeroes; - bool copy_range; + BlockCopyMethod method; QLIST_ENTRY(BlockCopyTask) list; CoQueue wait_queue; /* coroutines blocked on this task */ } BlockCopyTask; @@ -86,8 +93,8 @@ typedef struct BlockCopyState { BdrvDirtyBitmap *copy_bitmap; int64_t in_flight_bytes; int64_t cluster_size; - bool use_copy_range; - int64_t copy_size; + BlockCopyMethod method; + int64_t max_transfer; uint64_t len; QLIST_HEAD(, BlockCopyTask) tasks; /* All tasks from all block-copy calls */ QLIST_HEAD(, BlockCopyCallState) calls; @@ -149,6 +156,24 @@ static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t offset, return true; } +static int64_t block_copy_chunk_size(BlockCopyState *s) +{ + switch (s->method) { + case COPY_READ_WRITE_CLUSTER: + return s->cluster_size; + case COPY_READ_WRITE: + case COPY_RANGE_SMALL: + return MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER), + s->max_transfer); + case COPY_RANGE_FULL: + return MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_COPY_RANGE), + s->max_transfer); + default: + /* Cannot have COPY_WRITE_ZEROES here. */ + abort(); + } +} + /* * Search for the first dirty area in offset/bytes range and create task at * the beginning of it. @@ -158,8 +183,9 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s, int64_t offset, int64_t bytes) { BlockCopyTask *task; - int64_t max_chunk = MIN_NON_ZERO(s->copy_size, call_state->max_chunk); + int64_t max_chunk; + max_chunk = MIN_NON_ZERO(block_copy_chunk_size(s), call_state->max_chunk); if (!bdrv_dirty_bitmap_next_dirty_area(s->copy_bitmap, offset, offset + bytes, max_chunk, &offset, &bytes)) @@ -183,7 +209,7 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s, .call_state = call_state, .offset = offset, .bytes = bytes, - .copy_range = s->use_copy_range, + .method = s->method, }; qemu_co_queue_init(&task->wait_queue); QLIST_INSERT_HEAD(&s->tasks, task, list); @@ -267,28 +293,28 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target, .len = bdrv_dirty_bitmap_size(copy_bitmap), .write_flags = write_flags, .mem = shres_create(BLOCK_COPY_MAX_MEM), + .max_transfer = QEMU_ALIGN_DOWN( + block_copy_max_transfer(source, target), + cluster_size), }; - if (block_copy_max_transfer(source, target) < cluster_size) { + if (s->max_transfer < cluster_size) { /* * copy_range does not respect max_transfer. We don't want to bother * with requests smaller than block-copy cluster size, so fallback to * buffered copying (read and write respect max_transfer on their * behalf). */ - s->use_copy_range = false; - s->copy_size = cluster_size; + s->method = COPY_READ_WRITE_CLUSTER; } else if (write_flags & BDRV_REQ_WRITE_COMPRESSED) { /* Compression supports only cluster-size writes and no copy-range. */ - s->use_copy_range = false; - s->copy_size = cluster_size; + s->method = COPY_READ_WRITE_CLUSTER; } else { /* - * We enable copy-range, but keep small copy_size, until first + * If copy range enabled, start with COPY_RANGE_SMALL, until first * successful copy_range (look at block_copy_do_copy). */ - s->use_copy_range = use_copy_range; - s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER); + s->method = use_copy_range ? COPY_RANGE_SMALL : COPY_READ_WRITE; } ratelimit_init(&s->rate_limit); @@ -343,17 +369,14 @@ static coroutine_fn int block_copy_task_run(AioTaskPool *pool, * * No sync here: nor bitmap neighter intersecting requests handling, only copy. * - * @copy_range is an in-out argument: if *copy_range is false, copy_range is not - * done. If *copy_range is true, copy_range is attempted. If the copy_range - * attempt fails, the function falls back to the usual read+write and - * *copy_range is set to false. *copy_range and zeroes must not be true - * simultaneously. - * + * @method is an in-out argument, so that copy_range can be either extended to + * a full-size buffer or disabled if the copy_range attempt fails. The output + * value of @method should be used for subsequent tasks. * Returns 0 on success. */ static int coroutine_fn block_copy_do_copy(BlockCopyState *s, int64_t offset, int64_t bytes, - bool zeroes, bool *copy_range, + BlockCopyMethod *method, bool *error_is_read) { int ret; @@ -367,9 +390,9 @@ static int coroutine_fn block_copy_do_copy(BlockCopyState *s, assert(offset + bytes <= s->len || offset + bytes == QEMU_ALIGN_UP(s->len, s->cluster_size)); assert(nbytes < INT_MAX); - assert(!(*copy_range && zeroes)); - if (zeroes) { + switch (*method) { + case COPY_WRITE_ZEROES: ret = bdrv_co_pwrite_zeroes(s->target, offset, nbytes, s->write_flags & ~BDRV_REQ_WRITE_COMPRESSED); if (ret < 0) { @@ -377,90 +400,72 @@ static int coroutine_fn block_copy_do_copy(BlockCopyState *s, *error_is_read = false; } return ret; - } - if (*copy_range) { + case COPY_RANGE_SMALL: + case COPY_RANGE_FULL: ret = bdrv_co_copy_range(s->source, offset, s->target, offset, nbytes, 0, s->write_flags); - if (ret < 0) { - trace_block_copy_copy_range_fail(s, offset, ret); - *copy_range = false; - /* Fallback to read+write with allocated buffer */ - } else { + if (ret >= 0) { + /* Successful copy-range, increase chunk size. */ + *method = COPY_RANGE_FULL; return 0; } + + trace_block_copy_copy_range_fail(s, offset, ret); + *method = COPY_READ_WRITE; + /* Fall through to read+write with allocated buffer */ + + case COPY_READ_WRITE_CLUSTER: + case COPY_READ_WRITE: + /* + * In case of failed copy_range request above, we may proceed with + * buffered request larger than BLOCK_COPY_MAX_BUFFER. + * Still, further requests will be properly limited, so don't care too + * much. Moreover the most likely case (copy_range is unsupported for + * the configuration, so the very first copy_range request fails) + * is handled by setting large copy_size only after first successful + * copy_range. + */ + + bounce_buffer = qemu_blockalign(s->source->bs, nbytes); + + ret = bdrv_co_pread(s->source, offset, nbytes, bounce_buffer, 0); + if (ret < 0) { + trace_block_copy_read_fail(s, offset, ret); + *error_is_read = true; + goto out; + } + + ret = bdrv_co_pwrite(s->target, offset, nbytes, bounce_buffer, + s->write_flags); + if (ret < 0) { + trace_block_copy_write_fail(s, offset, ret); + *error_is_read = false; + goto out; + } + + out: + qemu_vfree(bounce_buffer); + break; + + default: + abort(); } - /* - * In case of failed copy_range request above, we may proceed with buffered - * request larger than BLOCK_COPY_MAX_BUFFER. Still, further requests will - * be properly limited, so don't care too much. Moreover the most likely - * case (copy_range is unsupported for the configuration, so the very first - * copy_range request fails) is handled by setting large copy_size only - * after first successful copy_range. - */ - - bounce_buffer = qemu_blockalign(s->source->bs, nbytes); - - ret = bdrv_co_pread(s->source, offset, nbytes, bounce_buffer, 0); - if (ret < 0) { - trace_block_copy_read_fail(s, offset, ret); - *error_is_read = true; - goto out; - } - - ret = bdrv_co_pwrite(s->target, offset, nbytes, bounce_buffer, - s->write_flags); - if (ret < 0) { - trace_block_copy_write_fail(s, offset, ret); - *error_is_read = false; - goto out; - } - -out: - qemu_vfree(bounce_buffer); - return ret; } -static void block_copy_handle_copy_range_result(BlockCopyState *s, - bool is_success) -{ - if (!s->use_copy_range) { - /* already disabled */ - return; - } - - if (is_success) { - /* - * Successful copy-range. Now increase copy_size. copy_range - * does not respect max_transfer (it's a TODO), so we factor - * that in here. - */ - s->copy_size = - MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_COPY_RANGE), - QEMU_ALIGN_DOWN(block_copy_max_transfer(s->source, - s->target), - s->cluster_size)); - } else { - /* Copy-range failed, disable it. */ - s->use_copy_range = false; - s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER); - } -} - static coroutine_fn int block_copy_task_entry(AioTask *task) { BlockCopyTask *t = container_of(task, BlockCopyTask, task); BlockCopyState *s = t->s; bool error_is_read = false; - bool copy_range = t->copy_range; + BlockCopyMethod method = t->method; int ret; - ret = block_copy_do_copy(s, t->offset, t->bytes, t->zeroes, - ©_range, &error_is_read); - if (t->copy_range) { - block_copy_handle_copy_range_result(s, copy_range); + ret = block_copy_do_copy(s, t->offset, t->bytes, &method, &error_is_read); + if (s->method == t->method) { + s->method = method; } if (ret < 0) { if (!t->call_state->ret) { @@ -643,8 +648,7 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state) continue; } if (ret & BDRV_BLOCK_ZERO) { - task->zeroes = true; - task->copy_range = false; + task->method = COPY_WRITE_ZEROES; } if (!call_state->ignore_ratelimit) {