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

[Fam Zheng <famz@redhat.com>]

On Thu, 05/26 09:55, Paolo Bonzini wrote:
> 
> 
> 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.

I've no idea. (That's why I leaned towards fixing the test case).  But if Kevin
can ack, I'd be happy with this way.

Fam