Re: [PATCH net-next RFC 2/5] vhost: introduce helper to prefetch desc index

On 2017年09月22日 17:02, Stefan Hajnoczi wrote:

On Fri, Sep 22, 2017 at 04:02:32PM +0800, Jason Wang wrote:

quoted

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f87ec75..8424166d 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -2437,6 +2437,61 @@ struct vhost_msg_node *vhost_dequeue_msg(struct vhost_dev *dev,
  }
  EXPORT_SYMBOL_GPL(vhost_dequeue_msg);
  
+int vhost_prefetch_desc_indices(struct vhost_virtqueue *vq,
+				struct vring_used_elem *heads,
+				u16 num, bool used_update)

Missing doc comment.

Will fix this.

quoted

+{
+	int ret, ret2;
+	u16 last_avail_idx, last_used_idx, total, copied;
+	__virtio16 avail_idx;
+	struct vring_used_elem __user *used;
+	int i;

The following variable names are a little confusing:

last_avail_idx vs vq->last_avail_idx.  last_avail_idx is a wrapped
avail->ring[] index, vq->last_avail_idx is a free-running counter.  The
same for last_used_idx vs vq->last_used_idx.

num argument vs vq->num.  The argument could be called nheads instead to
make it clear that this is heads[] and not the virtqueue size.

Not a bug but it took me a while to figure out what was going on.

I admit the name is confusing. Let me try better ones in V2.

Thanks