Re: [RFC V5 PATCH 8/8] vhost: event suppression for packed ring

[Jason Wang <jasowang@xxxxxxxxxx>]

On 2018年05月30日 19:42, Wei Xu wrote:
> >   /* This actually signals the guest, using eventfd. */
> >   void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> >   {
> > @@ -2802,10 +2930,34 @@ static bool vhost_enable_notify_packed(struct vhost_dev *dev,
> >   				       struct vhost_virtqueue *vq)
> >   {
> >   	struct vring_desc_packed *d = vq->desc_packed + vq->avail_idx;
> > -	__virtio16 flags;
> > +	__virtio16 flags = RING_EVENT_FLAGS_ENABLE;
> >   	int ret;
> >   
> > -	/* FIXME: disable notification through device area */
> > +	if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
> > +		return false;
> > +	vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
> 'used_flags' was originally designed for 1.0, why should we pay attetion to it here?
>
> Wei

It was used to recored whether or not we've disabled notification. Then 
we can avoid unnecessary userspace writes or memory barriers.

Thanks