On 27.11.19 19:08, Vladimir Sementsov-Ogievskiy wrote:
Currently, block_copy operation lock the whole requested region. But
there is no reason to lock clusters, which are already copied, it will
disturb other parallel block_copy requests for no reason.
Let's instead do the following:
Lock only sub-region, which we are going to operate on. Then, after
copying all dirty sub-regions, we should wait for intersecting
requests block-copy, if they failed, we should retry these new dirty
clusters.
Just a thought spoken aloud:
I would expect the number of intersecting CBW requests to be low in
general, so I don’t know how useful this change is in practice. OTOH,
it makes block_copy call the existing implementation in a loop, which
seems just worse.
But then again, in the common case, block_copy_dirty_clusters() won’t
copy anything because it’s all been copied already, so there is no
change; and even if something is copied, the second call will just
re-check the dirty bitmap to see that the area’s clean (which will be
quick compared to the copy operation). So there’s probably nothing to
worry about.
Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
block/block-copy.c | 116 +++++++++++++++++++++++++++++++++++++--------
1 file changed, 95 insertions(+), 21 deletions(-)
diff --git a/block/block-copy.c b/block/block-copy.c
index 20068cd699..aca44b13fb 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -39,29 +39,62 @@ static BlockCopyInFlightReq
*block_copy_find_inflight_req(BlockCopyState *s,
return NULL;
}
-static void coroutine_fn block_copy_wait_inflight_reqs(BlockCopyState *s,
- int64_t offset,
- int64_t bytes)
+/*
+ * If there are no intersecting requests return false. Otherwise, wait for the
+ * first found intersecting request to finish and return true.
+ */
+static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t start,
+ int64_t end)
s/end/bytes/?
(And maybe s/start/offset/, too)
{
- BlockCopyInFlightReq *req;
+ BlockCopyInFlightReq *req = block_copy_find_inflight_req(s, start, end);
- while ((req = block_copy_find_inflight_req(s, offset, bytes))) {
- qemu_co_queue_wait(&req->wait_queue, NULL);
+ if (!req) {
+ return false;
}
+
+ qemu_co_queue_wait(&req->wait_queue, NULL);
+
+ return true;
}
+/* Called only on full-dirty region */
static void block_copy_inflight_req_begin(BlockCopyState *s,
BlockCopyInFlightReq *req,
int64_t offset, int64_t bytes)
{
+ assert(!block_copy_find_inflight_req(s, offset, bytes));
+
+ bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, bytes);
+
req->offset = offset;
req->bytes = bytes;
qemu_co_queue_init(&req->wait_queue);
QLIST_INSERT_HEAD(&s->inflight_reqs, req, list);
}
-static void coroutine_fn block_copy_inflight_req_end(BlockCopyInFlightReq *req)
+static void coroutine_fn block_copy_inflight_req_shrink(BlockCopyState *s,
+ BlockCopyInFlightReq *req, int64_t new_bytes)
It took me a while to understand that this is operation drops the tail
of the request. I think there should be a comment on this.
(I thought it would successively drop the head after each copy, and so I
was wondering why the code didn’t match that.)
{
+ if (new_bytes == req->bytes) {
+ return;
+ }
+
+ assert(new_bytes > 0 && new_bytes < req->bytes);
+
+ bdrv_set_dirty_bitmap(s->copy_bitmap,
+ req->offset + new_bytes, req->bytes - new_bytes);> +
+ req->bytes = new_bytes;
+ qemu_co_queue_restart_all(&req->wait_queue);
+}
+
+static void coroutine_fn block_copy_inflight_req_end(BlockCopyState *s,
+ BlockCopyInFlightReq *req,
+ int ret)
+{
+ if (ret < 0) {
+ bdrv_set_dirty_bitmap(s->copy_bitmap, req->offset, req->bytes);
+ }
QLIST_REMOVE(req, list);
qemu_co_queue_restart_all(&req->wait_queue);
}
@@ -344,12 +377,19 @@ int64_t block_copy_reset_unallocated(BlockCopyState *s,
return ret;
}
-int coroutine_fn block_copy(BlockCopyState *s,
- int64_t offset, uint64_t bytes,
- bool *error_is_read)
+/*
+ * block_copy_dirty_clusters
+ *
+ * Copy dirty clusters in @start/@bytes range.
+ * Returns 1 if dirty clusters found and successfully copied, 0 if no dirty
+ * clusters found and -errno on failure.
+ */
+static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
+ int64_t offset, int64_t
bytes,
+ bool *error_is_read)
{
int ret = 0;
- BlockCopyInFlightReq req;
+ bool found_dirty = false;
/*
* block_copy() user is responsible for keeping source and target in same
@@ -361,10 +401,8 @@ int coroutine_fn block_copy(BlockCopyState *s,
assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
- block_copy_wait_inflight_reqs(s, offset, bytes);
- block_copy_inflight_req_begin(s, &req, offset, bytes);
-
while (bytes) {
+ BlockCopyInFlightReq req;
int64_t next_zero, cur_bytes, status_bytes;
if (!bdrv_dirty_bitmap_get(s->copy_bitmap, offset)) {
@@ -374,6 +412,8 @@ int coroutine_fn block_copy(BlockCopyState *s,
continue; /* already copied */
}
+ found_dirty = true;
+
cur_bytes = MIN(bytes, s->copy_size);
next_zero = bdrv_dirty_bitmap_next_zero(s->copy_bitmap, offset,
@@ -383,10 +423,12 @@ int coroutine_fn block_copy(BlockCopyState *s,
assert(next_zero < offset + cur_bytes); /* no need to do MIN() */
cur_bytes = next_zero - offset;
}
+ block_copy_inflight_req_begin(s, &req, offset, cur_bytes);
ret = block_copy_block_status(s, offset, cur_bytes, &status_bytes);
+ block_copy_inflight_req_shrink(s, &req, status_bytes);
block_copy_inflight_req_shrink() asserts that status_bytes <= cur_bytes.
That isn’t necessarily correct, as block_copy_block_status() rounds up
on the last cluster. So this should use the same MIN() as for the
cur_bytes update after the next block.
Would it make sense to move the block_copy_inflight_req_shrink() there
and pass the updated cur_bytes to it?
if (s->skip_unallocated && !(ret & BDRV_BLOCK_ALLOCATED)) {
- bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, status_bytes);
+ block_copy_inflight_req_end(s, &req, 0);
s->progress_reset_callback(s->progress_opaque);
trace_block_copy_skip_range(s, offset, status_bytes);
offset += status_bytes;
@@ -398,15 +440,13 @@ int coroutine_fn block_copy(BlockCopyState *s,
trace_block_copy_process(s, offset);
- bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, cur_bytes);
-
co_get_from_shres(s->mem, cur_bytes);
ret = block_copy_do_copy(s, offset, cur_bytes, ret & BDRV_BLOCK_ZERO,
error_is_read);
co_put_to_shres(s->mem, cur_bytes);
+ block_copy_inflight_req_end(s, &req, ret);
if (ret < 0) {
- bdrv_set_dirty_bitmap(s->copy_bitmap, offset, cur_bytes);
- break;
+ return ret;
}
s->progress_bytes_callback(cur_bytes, s->progress_opaque);
@@ -414,7 +454,41 @@ int coroutine_fn block_copy(BlockCopyState *s,
bytes -= cur_bytes;
}
- block_copy_inflight_req_end(&req);
+ return found_dirty;
+}
- return ret;
+int coroutine_fn block_copy(BlockCopyState *s, int64_t start, uint64_t bytes,
+ bool *error_is_read)
+{
+ while (true) {
+ int ret = block_copy_dirty_clusters(s, start, bytes, error_is_read);
+
+ if (ret < 0) {
+ /*
+ * IO operation failed, which means the whole block_copy request
+ * failed.
+ */
+ return ret;
+ }
+ if (ret) {
+ /*
+ * Something was copied, which means that there were yield points
+ * and some new dirty bits may appered (due to failed parallel
s/appered/have appeared/
+ * block-copy requests).
+ */
+ continue;
+ }
+
+ /*
+ * Here ret == 0, which means that there is no dirty clusters in
+ * requested region.
+ */
+
+ if (!block_copy_wait_one(s, start, bytes)) {
+ /* No dirty bits and nothing to wait: the whole request is done */
Wouldn’t it make more sense to keep block_copy_wait_one() a loop (i.e.,
keep it as block_copy_wait_inflight_reqs()) that returns whether it
waited or not? Because I suppose if we had to wait for anything, we
might as well wait for everything in the range.