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block-copy: streamline choice of copy_range vs. read/write

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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>
This commit is contained in:
Paolo Bonzini 2021-06-24 09:20:40 +02:00 committed by Vladimir Sementsov-Ogievskiy
parent c6a3e3df30
commit 05d5e12b24
1 changed files with 96 additions and 92 deletions
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188
block/block-copy.c
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@ -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,
&copy_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) {