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

[Wei Xu <wexu@redhat.com>]

On Thu, May 31, 2018 at 11:09:07AM +0800, Jason Wang wrote:
> 
> 
> 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.

OK, thanks.

> 
> Thanks