Re: [Qemu-devel] [PATCH v3 15/29] block: Allow waiting for overlapping requests between begin/end

["Benoît Canet" <benoit.canet@irqsave.net>]

Le Friday 17 Jan 2014 à 15:15:05 (+0100), Kevin Wolf a écrit :
> Previously, it was not possible to use wait_for_overlapping_requests()
> between tracked_request_begin()/end() because it would wait for itself.
> 
> Ignore the current request in the overlap check and run more of the
> bdrv_co_do_preadv/pwritev code with a BdrvTrackedRequest present.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c | 38 ++++++++++++++++++++------------------
>  1 file changed, 20 insertions(+), 18 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 85f28ab..18dcd43 100644
> --- a/block.c
> +++ b/block.c
> @@ -2106,7 +2106,7 @@ static bool tracked_request_overlaps(BdrvTrackedRequest *req,
>  }
>  
>  static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
> -        int64_t offset, unsigned int bytes)
> +        BdrvTrackedRequest *self, int64_t offset, unsigned int bytes)
>  {
>      BdrvTrackedRequest *req;
>      int64_t cluster_offset;
> @@ -2124,6 +2124,9 @@ static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
>      do {
>          retry = false;
>          QLIST_FOREACH(req, &bs->tracked_requests, list) {
> +            if (req == self) {
> +                continue;
> +            }
>              if (tracked_request_overlaps(req, cluster_offset, cluster_bytes)) {
>                  /* Hitting this means there was a reentrant request, for
>                   * example, a block driver issuing nested requests.  This must
> @@ -2726,10 +2729,10 @@ err:
>   * implemented by the caller.
>   */
>  static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
> -    int64_t offset, unsigned int bytes, QEMUIOVector *qiov, int flags)
> +    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
> +    QEMUIOVector *qiov, int flags)
>  {
>      BlockDriver *drv = bs->drv;
> -    BdrvTrackedRequest req;
>      int ret;
>  
>      int64_t sector_num = offset >> BDRV_SECTOR_BITS;
> @@ -2744,11 +2747,9 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
>      }
>  
>      if (bs->copy_on_read_in_flight) {
> -        wait_for_overlapping_requests(bs, offset, bytes);
> +        wait_for_overlapping_requests(bs, req, offset, bytes);
>      }
>  
> -    tracked_request_begin(&req, bs, offset, bytes, false);
> -
>      if (flags & BDRV_REQ_COPY_ON_READ) {
>          int pnum;
>  
> @@ -2795,8 +2796,6 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
>      }
>  
>  out:
> -    tracked_request_end(&req);
> -
>      if (flags & BDRV_REQ_COPY_ON_READ) {
>          bs->copy_on_read_in_flight--;
>      }
> @@ -2812,6 +2811,8 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
>      BdrvRequestFlags flags)
>  {
>      BlockDriver *drv = bs->drv;
> +    BdrvTrackedRequest req;
> +
>      /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
>      uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
>      uint8_t *head_buf = NULL;
> @@ -2862,9 +2863,11 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
>          bytes = ROUND_UP(bytes, align);
>      }
>  
> -    ret = bdrv_aligned_preadv(bs, offset, bytes,
> +    tracked_request_begin(&req, bs, offset, bytes, false);
> +    ret = bdrv_aligned_preadv(bs, &req, offset, bytes,
>                                use_local_qiov ? &local_qiov : qiov,
>                                flags);
> +    tracked_request_end(&req);
>  
>      if (use_local_qiov) {
>          qemu_iovec_destroy(&local_qiov);
> @@ -2983,10 +2986,10 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
>   * Forwards an already correctly aligned write request to the BlockDriver.
>   */
>  static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
> -    int64_t offset, unsigned int bytes, QEMUIOVector *qiov, int flags)
> +    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
> +    QEMUIOVector *qiov, int flags)
>  {
>      BlockDriver *drv = bs->drv;
> -    BdrvTrackedRequest req;
>      int ret;
>  
>      int64_t sector_num = offset >> BDRV_SECTOR_BITS;
> @@ -2996,12 +2999,10 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
>      assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
>  
>      if (bs->copy_on_read_in_flight) {
> -        wait_for_overlapping_requests(bs, offset, bytes);
> +        wait_for_overlapping_requests(bs, req, offset, bytes);
>      }
>  
> -    tracked_request_begin(&req, bs, offset, bytes, true);
> -
> -    ret = notifier_with_return_list_notify(&bs->before_write_notifiers, &req);
> +    ret = notifier_with_return_list_notify(&bs->before_write_notifiers, req);
>  
>      if (ret < 0) {
>          /* Do nothing, write notifier decided to fail this request */
> @@ -3024,8 +3025,6 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
>          bs->total_sectors = MAX(bs->total_sectors, sector_num + nb_sectors);
>      }
>  
> -    tracked_request_end(&req);
> -
>      return ret;
>  }
>  
> @@ -3036,6 +3035,7 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
>      int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
>      BdrvRequestFlags flags)
>  {
> +    BdrvTrackedRequest req;
>      int ret;
>  
>      if (!bs->drv) {
> @@ -3054,7 +3054,9 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
>          bdrv_io_limits_intercept(bs, bytes >> BDRV_SECTOR_BITS, true);
>      }
>  
> -    ret = bdrv_aligned_pwritev(bs, offset, bytes, qiov, flags);
> +    tracked_request_begin(&req, bs, offset, bytes, true);
> +    ret = bdrv_aligned_pwritev(bs, &req, offset, bytes, qiov, flags);
> +    tracked_request_end(&req);
>  
>      return ret;
>  }
> -- 
> 1.8.1.4
> 
> 
Reviewed-by: Benoit Canet <benoit@irqsave.net>