Re: [PATCH v2 6/7] block/block-copy: reduce intersecting request lock

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

On 27/11/2019 21:08, 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.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   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)
>   {
> -    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)
>   {
> +    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)

I suggest substituting the 'int ret' parameter with someone like 'bool 
set_dirty' and pass the expression 'ret < 0' as the input parameter in 
calling function. The 'int ret' is used in QEMU as a local return 
variable traditionally.

> +{
> +    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);
>           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
> +             * 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 */
> +            break;
> +        }
> +    }
> +
> +    return 0;
>   }
> 

-- 
With the best regards,
Andrey Shinkevich