Re: [PATCH v2 4/7] block/block-copy: refactor interfaces to use bytes instead of end

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

On 27/11/2019 21:08, Vladimir Sementsov-Ogievskiy wrote:
> We have a lot of "chunk_end - start" invocations, let's switch to
> bytes/cur_bytes scheme instead.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   include/block/block-copy.h |  4 +--
>   block/block-copy.c         | 68 ++++++++++++++++++++------------------
>   2 files changed, 37 insertions(+), 35 deletions(-)
> 
> diff --git a/include/block/block-copy.h b/include/block/block-copy.h
> index 0a161724d7..7321b3d305 100644
> --- a/include/block/block-copy.h
> +++ b/include/block/block-copy.h
> @@ -19,8 +19,8 @@
>   #include "qemu/co-shared-resource.h"
>   
>   typedef struct BlockCopyInFlightReq {
> -    int64_t start_byte;
> -    int64_t end_byte;
> +    int64_t start;
> +    int64_t bytes;
>       QLIST_ENTRY(BlockCopyInFlightReq) list;
>       CoQueue wait_queue; /* coroutines blocked on this request */
>   } BlockCopyInFlightReq;
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 94e7e855ef..cc273b6cb8 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c
> @@ -26,12 +26,12 @@
>   
>   static BlockCopyInFlightReq *block_copy_find_inflight_req(BlockCopyState *s,
>                                                             int64_t start,
> -                                                          int64_t end)
> +                                                          int64_t bytes)
>   {
>       BlockCopyInFlightReq *req;
>   
>       QLIST_FOREACH(req, &s->inflight_reqs, list) {
> -        if (end > req->start_byte && start < req->end_byte) {
> +        if (start + bytes > req->start && start < req->start + req->bytes) {
>               return req;
>           }
>       }
> @@ -41,21 +41,21 @@ static BlockCopyInFlightReq *block_copy_find_inflight_req(BlockCopyState *s,
>   
>   static void coroutine_fn block_copy_wait_inflight_reqs(BlockCopyState *s,
>                                                          int64_t start,
> -                                                       int64_t end)
> +                                                       int64_t bytes)
>   {
>       BlockCopyInFlightReq *req;
>   
> -    while ((req = block_copy_find_inflight_req(s, start, end))) {
> +    while ((req = block_copy_find_inflight_req(s, start, bytes))) {
>           qemu_co_queue_wait(&req->wait_queue, NULL);
>       }
>   }
>   
>   static void block_copy_inflight_req_begin(BlockCopyState *s,
>                                             BlockCopyInFlightReq *req,
> -                                          int64_t start, int64_t end)
> +                                          int64_t start, int64_t bytes)
>   {
> -    req->start_byte = start;
> -    req->end_byte = end;
> +    req->start = start;
> +    req->bytes = bytes;
>       qemu_co_queue_init(&req->wait_queue);
>       QLIST_INSERT_HEAD(&s->inflight_reqs, req, list);
>   }
> @@ -150,24 +150,26 @@ void block_copy_set_callbacks(
>   /*
>    * block_copy_do_copy
>    *
> - * Do copy of cluser-aligned chunk. @end is allowed to exceed s->len only to
> - * cover last cluster when s->len is not aligned to clusters.
> + * Do copy of cluser-aligned chunk. Requested region is allowed to exceed s->len

cluster-...

> + * only to cover last cluster when s->len is not aligned to clusters.
>    *
>    * No sync here: nor bitmap neighter intersecting requests handling, only copy.
>    *
>    * Returns 0 on success.
>    */
>   static int coroutine_fn block_copy_do_copy(BlockCopyState *s,
> -                                           int64_t start, int64_t end,
> +                                           int64_t start, int64_t bytes,
>                                              bool zeroes, bool *error_is_read)
>   {
>       int ret;
> -    int nbytes = MIN(end, s->len) - start;
> +    int nbytes = MIN(start + bytes, s->len) - start;
>       void *bounce_buffer = NULL;
>   
> +    assert(start >= 0 && bytes > 0 && INT64_MAX - start >= bytes);
>       assert(QEMU_IS_ALIGNED(start, s->cluster_size));
> -    assert(QEMU_IS_ALIGNED(end, s->cluster_size));
> -    assert(end < s->len || end == QEMU_ALIGN_UP(s->len, s->cluster_size));
> +    assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
> +    assert(start + bytes <= s->len ||

The '<=' looks correct but I wonder how only '<' worked without 
assertion failure before. Was the s->len never aligned to the cluster size?

> +           start + bytes == QEMU_ALIGN_UP(s->len, s->cluster_size));
>   
>       if (zeroes) {
>           ret = bdrv_co_pwrite_zeroes(s->target, start, nbytes, s->write_flags &
> @@ -347,7 +349,6 @@ int coroutine_fn block_copy(BlockCopyState *s,
>                               bool *error_is_read)
>   {
>       int ret = 0;
> -    int64_t end = bytes + start; /* bytes */
>       BlockCopyInFlightReq req;
>   
>       /*
> @@ -358,58 +359,59 @@ int coroutine_fn block_copy(BlockCopyState *s,
>              bdrv_get_aio_context(s->target->bs));
>   
>       assert(QEMU_IS_ALIGNED(start, s->cluster_size));
> -    assert(QEMU_IS_ALIGNED(end, s->cluster_size));
> +    assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
>   
>       block_copy_wait_inflight_reqs(s, start, bytes);
> -    block_copy_inflight_req_begin(s, &req, start, end);
> +    block_copy_inflight_req_begin(s, &req, start, bytes);
>   
> -    while (start < end) {
> -        int64_t next_zero, chunk_end, status_bytes;
> +    while (bytes) {
> +        int64_t next_zero, cur_bytes, status_bytes;
>   
>           if (!bdrv_dirty_bitmap_get(s->copy_bitmap, start)) {
>               trace_block_copy_skip(s, start);
>               start += s->cluster_size;
> +            bytes -= s->cluster_size;
>               continue; /* already copied */
>           }
>   
> -        chunk_end = MIN(end, start + s->copy_size);
> +        cur_bytes = MIN(bytes, s->copy_size);
>   
>           next_zero = bdrv_dirty_bitmap_next_zero(s->copy_bitmap, start,
> -                                                chunk_end - start);
> +                                                cur_bytes);
>           if (next_zero >= 0) {
>               assert(next_zero > start); /* start is dirty */
> -            assert(next_zero < chunk_end); /* no need to do MIN() */
> -            chunk_end = next_zero;
> +            assert(next_zero < start + cur_bytes); /* no need to do MIN() */
> +            cur_bytes = next_zero - start;
>           }
>   
> -        ret = block_copy_block_status(s, start, chunk_end - start,
> -                                      &status_bytes);
> +        ret = block_copy_block_status(s, start, cur_bytes, &status_bytes);
>           if (s->skip_unallocated && !(ret & BDRV_BLOCK_ALLOCATED)) {
>               bdrv_reset_dirty_bitmap(s->copy_bitmap, start, status_bytes);
>               s->progress_reset_callback(s->progress_opaque);
>               trace_block_copy_skip_range(s, start, status_bytes);
>               start += status_bytes;
> +            bytes -= status_bytes;
>               continue;
>           }
>   
> -        chunk_end = MIN(chunk_end, start + status_bytes);
> +        cur_bytes = MIN(cur_bytes, status_bytes);
>   
>           trace_block_copy_process(s, start);
>   
> -        bdrv_reset_dirty_bitmap(s->copy_bitmap, start, chunk_end - start);
> +        bdrv_reset_dirty_bitmap(s->copy_bitmap, start, cur_bytes);
>   
> -        co_get_from_shres(s->mem, chunk_end - start);
> -        ret = block_copy_do_copy(s, start, chunk_end, ret & BDRV_BLOCK_ZERO,
> +        co_get_from_shres(s->mem, cur_bytes);
> +        ret = block_copy_do_copy(s, start, cur_bytes, ret & BDRV_BLOCK_ZERO,
>                                    error_is_read);
> -        co_put_to_shres(s->mem, chunk_end - start);
> +        co_put_to_shres(s->mem, cur_bytes);
>           if (ret < 0) {
> -            bdrv_set_dirty_bitmap(s->copy_bitmap, start, chunk_end - start);
> +            bdrv_set_dirty_bitmap(s->copy_bitmap, start, cur_bytes);
>               break;
>           }
>   
> -        s->progress_bytes_callback(chunk_end - start, s->progress_opaque);
> -        start = chunk_end;
> -        ret = 0;
> +        s->progress_bytes_callback(cur_bytes, s->progress_opaque);
> +        start += cur_bytes;
> +        bytes -= cur_bytes;
>       }
>   
>       block_copy_inflight_req_end(&req);
> 

At the first glance, we would only benefit from the 'while' loop by that 
substitution to reduce the number of addition operations.

Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
-- 
With the best regards,
Andrey Shinkevich