Re: [Qemu-devel] [PATCH v6 12/12] virtio-blk: add x-data-plane=on|off performance feature

[Stefan Hajnoczi <stefanha@gmail.com>]

On Sun, Dec 16, 2012 at 06:08:53PM +0200, Michael S. Tsirkin wrote:
> On Mon, Dec 10, 2012 at 02:09:45PM +0100, Stefan Hajnoczi wrote:
> > @@ -33,6 +34,7 @@ typedef struct VirtIOBlock
> >      VirtIOBlkConf *blk;
> >      unsigned short sector_mask;
> >      DeviceState *qdev;
> > +    VirtIOBlockDataPlane *dataplane;
> >  } VirtIOBlock;
> >  
> >  static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
> > @@ -407,6 +409,14 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
> >          .num_writes = 0,
> >      };
> >  
> > +    /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
> > +     * dataplane here instead of waiting for .set_status().
> > +     */
> 
> By the way which guests are these?

I ran a Windows 8 guest today with build 48 virtio-win drivers.  It
notifies before the device gets its .set_status() callback invoked.

But I could swear I've seen Linux guests do this too.

> > +    if (s->dataplane) {
> > +        virtio_blk_data_plane_start(s->dataplane);
> > +        return;
> > +    }
> > +
> 
> By the way it's chunk such as this that I meant: it's not
> compiled out even if dataplane is disabled by configure.
> Naither is the extra field in the struct.

Okay.

Stefan