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

[Vladimir Sementsov-Ogievskiy]

30.01.2020 18:53, Andrey Shinkevich wrote:
> 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 <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)
> >   {
> > -    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.


"int ret" is normal practice also for completion functions, look at 
bdrv_co_io_em_complete, bdrv_co_write_req_finish, do git grep '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);
> >           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;
> >   }


--
Best regards,
Vladimir