Re: [Qemu-devel] [PATCHv7 10/17] block: honour BlockLimits in bdrv_co_discard

[Kevin Wolf <kwolf@redhat.com>]

Am 24.10.2013 um 12:06 hat Peter Lieven geschrieben:
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  block.c |   37 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index 0c0b0ac..b28dd42 100644
> --- a/block.c
> +++ b/block.c
> @@ -4234,6 +4234,11 @@ static void coroutine_fn bdrv_discard_co_entry(void *opaque)
>      rwco->ret = bdrv_co_discard(rwco->bs, rwco->sector_num, rwco->nb_sectors);
>  }
>  
> +/* if no limit is specified in the BlockLimits use a default
> + * of 32768 512-byte sectors (16 MiB) per request.
> + */
> +#define MAX_DISCARD_DEFAULT 32768
> +
>  int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
>                                   int nb_sectors)
>  {
> @@ -4255,7 +4260,37 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
>      }
>  
>      if (bs->drv->bdrv_co_discard) {
> -        return bs->drv->bdrv_co_discard(bs, sector_num, nb_sectors);
> +        int max_discard = bs->bl.max_discard ?
> +                          bs->bl.max_discard : MAX_DISCARD_DEFAULT;
> +
> +        while (nb_sectors > 0) {
> +            int ret;
> +            int num = nb_sectors;
> +
> +            /* align request */
> +            if (bs->bl.discard_alignment &&
> +                num >= bs->bl.discard_alignment &&
> +                sector_num % bs->bl.discard_alignment) {
> +                if (num > bs->bl.discard_alignment) {
> +                    num = bs->bl.discard_alignment;
> +                }
> +                num -= sector_num % bs->bl.discard_alignment;
> +            }
> +
> +            /* limit request size */
> +            if (num > max_discard) {
> +                num = max_discard;
> +            }
> +
> +            ret = bs->drv->bdrv_co_discard(bs, sector_num, num);
> +            if (ret) {
> +                return ret;
> +            }
> +
> +            sector_num += num;
> +            nb_sectors -= num;
> +        }
> +        return 0;
>      } else if (bs->drv->bdrv_aio_discard) {
>          BlockDriverAIOCB *acb;
>          CoroutineIOCompletion co = {

You're only optimising drivers which have a .bdrv_co_discard()
implementation, but not those with .bdrv_aio_discard(). Not very nice,
and it would have been easy to avoid this by putting the loop around the
whole if statement instead of inside the 'then' branch.

Kevin