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https://gitlab.com/qemu-project/qemu
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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 <vsementsov@virtuozzo.com> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20210624072043.180494-3-eesposit@redhat.com> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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05d5e12b24
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@ -28,6 +28,14 @@
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#define BLOCK_COPY_MAX_WORKERS 64
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#define BLOCK_COPY_SLICE_TIME 100000000ULL /* ns */
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typedef enum {
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COPY_READ_WRITE_CLUSTER,
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COPY_READ_WRITE,
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COPY_WRITE_ZEROES,
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COPY_RANGE_SMALL,
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COPY_RANGE_FULL
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} BlockCopyMethod;
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static coroutine_fn int block_copy_task_entry(AioTask *task);
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typedef struct BlockCopyCallState {
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@ -64,8 +72,7 @@ typedef struct BlockCopyTask {
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BlockCopyCallState *call_state;
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int64_t offset;
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int64_t bytes;
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bool zeroes;
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bool copy_range;
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BlockCopyMethod method;
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QLIST_ENTRY(BlockCopyTask) list;
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CoQueue wait_queue; /* coroutines blocked on this task */
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} BlockCopyTask;
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@ -86,8 +93,8 @@ typedef struct BlockCopyState {
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BdrvDirtyBitmap *copy_bitmap;
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int64_t in_flight_bytes;
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int64_t cluster_size;
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bool use_copy_range;
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int64_t copy_size;
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BlockCopyMethod method;
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int64_t max_transfer;
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uint64_t len;
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QLIST_HEAD(, BlockCopyTask) tasks; /* All tasks from all block-copy calls */
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QLIST_HEAD(, BlockCopyCallState) calls;
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@ -149,6 +156,24 @@ static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t offset,
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return true;
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}
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static int64_t block_copy_chunk_size(BlockCopyState *s)
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{
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switch (s->method) {
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case COPY_READ_WRITE_CLUSTER:
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return s->cluster_size;
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case COPY_READ_WRITE:
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case COPY_RANGE_SMALL:
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return MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER),
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s->max_transfer);
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case COPY_RANGE_FULL:
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return MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_COPY_RANGE),
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s->max_transfer);
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default:
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/* Cannot have COPY_WRITE_ZEROES here. */
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abort();
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}
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}
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/*
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* Search for the first dirty area in offset/bytes range and create task at
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* the beginning of it.
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@ -158,8 +183,9 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
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int64_t offset, int64_t bytes)
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{
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BlockCopyTask *task;
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int64_t max_chunk = MIN_NON_ZERO(s->copy_size, call_state->max_chunk);
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int64_t max_chunk;
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max_chunk = MIN_NON_ZERO(block_copy_chunk_size(s), call_state->max_chunk);
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if (!bdrv_dirty_bitmap_next_dirty_area(s->copy_bitmap,
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offset, offset + bytes,
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max_chunk, &offset, &bytes))
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@ -183,7 +209,7 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
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.call_state = call_state,
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.offset = offset,
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.bytes = bytes,
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.copy_range = s->use_copy_range,
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.method = s->method,
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};
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qemu_co_queue_init(&task->wait_queue);
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QLIST_INSERT_HEAD(&s->tasks, task, list);
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@ -267,28 +293,28 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
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.len = bdrv_dirty_bitmap_size(copy_bitmap),
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.write_flags = write_flags,
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.mem = shres_create(BLOCK_COPY_MAX_MEM),
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.max_transfer = QEMU_ALIGN_DOWN(
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block_copy_max_transfer(source, target),
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cluster_size),
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};
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if (block_copy_max_transfer(source, target) < cluster_size) {
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if (s->max_transfer < cluster_size) {
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/*
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* copy_range does not respect max_transfer. We don't want to bother
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* with requests smaller than block-copy cluster size, so fallback to
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* buffered copying (read and write respect max_transfer on their
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* behalf).
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*/
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s->use_copy_range = false;
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s->copy_size = cluster_size;
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s->method = COPY_READ_WRITE_CLUSTER;
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} else if (write_flags & BDRV_REQ_WRITE_COMPRESSED) {
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/* Compression supports only cluster-size writes and no copy-range. */
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s->use_copy_range = false;
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s->copy_size = cluster_size;
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s->method = COPY_READ_WRITE_CLUSTER;
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} else {
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/*
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* We enable copy-range, but keep small copy_size, until first
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* If copy range enabled, start with COPY_RANGE_SMALL, until first
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* successful copy_range (look at block_copy_do_copy).
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*/
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s->use_copy_range = use_copy_range;
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s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
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s->method = use_copy_range ? COPY_RANGE_SMALL : COPY_READ_WRITE;
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}
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ratelimit_init(&s->rate_limit);
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@ -343,17 +369,14 @@ static coroutine_fn int block_copy_task_run(AioTaskPool *pool,
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*
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* No sync here: nor bitmap neighter intersecting requests handling, only copy.
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*
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* @copy_range is an in-out argument: if *copy_range is false, copy_range is not
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* done. If *copy_range is true, copy_range is attempted. If the copy_range
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* attempt fails, the function falls back to the usual read+write and
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* *copy_range is set to false. *copy_range and zeroes must not be true
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* simultaneously.
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*
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* @method is an in-out argument, so that copy_range can be either extended to
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* a full-size buffer or disabled if the copy_range attempt fails. The output
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* value of @method should be used for subsequent tasks.
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* Returns 0 on success.
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*/
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static int coroutine_fn block_copy_do_copy(BlockCopyState *s,
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int64_t offset, int64_t bytes,
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bool zeroes, bool *copy_range,
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BlockCopyMethod *method,
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bool *error_is_read)
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{
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int ret;
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@ -367,9 +390,9 @@ static int coroutine_fn block_copy_do_copy(BlockCopyState *s,
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assert(offset + bytes <= s->len ||
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offset + bytes == QEMU_ALIGN_UP(s->len, s->cluster_size));
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assert(nbytes < INT_MAX);
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assert(!(*copy_range && zeroes));
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if (zeroes) {
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switch (*method) {
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case COPY_WRITE_ZEROES:
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ret = bdrv_co_pwrite_zeroes(s->target, offset, nbytes, s->write_flags &
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~BDRV_REQ_WRITE_COMPRESSED);
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if (ret < 0) {
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@ -377,90 +400,72 @@ static int coroutine_fn block_copy_do_copy(BlockCopyState *s,
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*error_is_read = false;
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}
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return ret;
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}
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if (*copy_range) {
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case COPY_RANGE_SMALL:
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case COPY_RANGE_FULL:
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ret = bdrv_co_copy_range(s->source, offset, s->target, offset, nbytes,
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0, s->write_flags);
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if (ret < 0) {
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trace_block_copy_copy_range_fail(s, offset, ret);
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*copy_range = false;
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/* Fallback to read+write with allocated buffer */
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} else {
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if (ret >= 0) {
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/* Successful copy-range, increase chunk size. */
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*method = COPY_RANGE_FULL;
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return 0;
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}
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trace_block_copy_copy_range_fail(s, offset, ret);
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*method = COPY_READ_WRITE;
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/* Fall through to read+write with allocated buffer */
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case COPY_READ_WRITE_CLUSTER:
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case COPY_READ_WRITE:
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/*
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* In case of failed copy_range request above, we may proceed with
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* buffered request larger than BLOCK_COPY_MAX_BUFFER.
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* Still, further requests will be properly limited, so don't care too
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* much. Moreover the most likely case (copy_range is unsupported for
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* the configuration, so the very first copy_range request fails)
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* is handled by setting large copy_size only after first successful
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* copy_range.
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*/
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bounce_buffer = qemu_blockalign(s->source->bs, nbytes);
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ret = bdrv_co_pread(s->source, offset, nbytes, bounce_buffer, 0);
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if (ret < 0) {
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trace_block_copy_read_fail(s, offset, ret);
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*error_is_read = true;
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goto out;
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}
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ret = bdrv_co_pwrite(s->target, offset, nbytes, bounce_buffer,
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s->write_flags);
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if (ret < 0) {
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trace_block_copy_write_fail(s, offset, ret);
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*error_is_read = false;
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goto out;
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}
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out:
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qemu_vfree(bounce_buffer);
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break;
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default:
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abort();
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}
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/*
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* In case of failed copy_range request above, we may proceed with buffered
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* request larger than BLOCK_COPY_MAX_BUFFER. Still, further requests will
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* be properly limited, so don't care too much. Moreover the most likely
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* case (copy_range is unsupported for the configuration, so the very first
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* copy_range request fails) is handled by setting large copy_size only
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* after first successful copy_range.
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*/
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bounce_buffer = qemu_blockalign(s->source->bs, nbytes);
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ret = bdrv_co_pread(s->source, offset, nbytes, bounce_buffer, 0);
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if (ret < 0) {
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trace_block_copy_read_fail(s, offset, ret);
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*error_is_read = true;
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goto out;
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}
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ret = bdrv_co_pwrite(s->target, offset, nbytes, bounce_buffer,
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s->write_flags);
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if (ret < 0) {
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trace_block_copy_write_fail(s, offset, ret);
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*error_is_read = false;
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goto out;
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}
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out:
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qemu_vfree(bounce_buffer);
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return ret;
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}
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static void block_copy_handle_copy_range_result(BlockCopyState *s,
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bool is_success)
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{
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if (!s->use_copy_range) {
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/* already disabled */
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return;
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}
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if (is_success) {
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/*
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* Successful copy-range. Now increase copy_size. copy_range
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* does not respect max_transfer (it's a TODO), so we factor
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* that in here.
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*/
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s->copy_size =
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MIN(MAX(s->cluster_size, BLOCK_COPY_MAX_COPY_RANGE),
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QEMU_ALIGN_DOWN(block_copy_max_transfer(s->source,
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s->target),
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s->cluster_size));
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} else {
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/* Copy-range failed, disable it. */
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s->use_copy_range = false;
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s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
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}
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}
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static coroutine_fn int block_copy_task_entry(AioTask *task)
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{
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BlockCopyTask *t = container_of(task, BlockCopyTask, task);
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BlockCopyState *s = t->s;
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bool error_is_read = false;
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bool copy_range = t->copy_range;
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BlockCopyMethod method = t->method;
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int ret;
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ret = block_copy_do_copy(s, t->offset, t->bytes, t->zeroes,
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©_range, &error_is_read);
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if (t->copy_range) {
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block_copy_handle_copy_range_result(s, copy_range);
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ret = block_copy_do_copy(s, t->offset, t->bytes, &method, &error_is_read);
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if (s->method == t->method) {
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s->method = method;
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}
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if (ret < 0) {
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if (!t->call_state->ret) {
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@ -643,8 +648,7 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
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continue;
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}
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if (ret & BDRV_BLOCK_ZERO) {
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task->zeroes = true;
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task->copy_range = false;
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task->method = COPY_WRITE_ZEROES;
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}
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if (!call_state->ignore_ratelimit) {
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