Re: [PATCH v2 02/24] virtio: Use weaker barriers

I recall our original code is virtio_wmb(). 
Use store fence to ensure all updates to entries before updating the index.
Why do we need virtio_rmb() here and add virtio_wmb after vq_update_avail_idx()?

Store fence is unnecessary, Intel CPU's are cache coherent, please read
the virtio Linux ring header file for explanation. A full fence WMB
is more expensive and causes CPU stall

quoted

 	vq->vq_ring.avail->idx = vq->vq_avail_idx;
 }

@@ -255,7 +264,7 @@ static inline void
 virtqueue_notify(struct virtqueue *vq)
 {
 	/*
-	 * Ensure updated avail->idx is visible to host. mb() necessary?
+	 * Ensure updated avail->idx is visible to host.
 	 * For virtio on IA, the notificaiton is through io port operation
 	 * which is a serialization instruction itself.
 	 */
--

1.8.4.2