Re: [Qemu-block] [Qemu-devel] [PATCH V2] block/io: optimize bdrv_co_pwritev for small requests

[Paolo Bonzini]

On 26/05/2016 09:10, Fam Zheng wrote:
> 
> diff --git a/block/io.c b/block/io.c
> index d480097..a6523cf 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1435,8 +1435,10 @@ int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs,
>           * than one aligned block.
>           */
>          if (bytes < align) {
> +            bdrv_debug_event(bs, BLKDBG_PWRITEV_RMW_TAIL);
>              qemu_iovec_add(&local_qiov, head_buf + bytes, align - bytes);
>              bytes = align;
> +            bdrv_debug_event(bs, BLKDBG_PWRITEV_RMW_AFTER_TAIL);
>          }
>      }

This doesn't look too wrong...  Should the right sequence of events be
head/after_head or head/after_tail?  It's probably simplest to just emit
all four events.

Paolo