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Subject: Re: [RFC PATCH net-next v2 2/2] virtio_net: Extend virtio to use VF datapath when available

On 2018年01月24日 00:03, Samudrala, Sridhar wrote:

On 1/23/2018 2:33 AM, Jason Wang wrote:

On 2018年01月12日 13:58, Sridhar Samudrala wrote:
  static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
      struct virtnet_info *vi = netdev_priv(dev);
      int qnum = skb_get_queue_mapping(skb);
      struct send_queue *sq = &vi->sq[qnum];
+    struct net_device *vf_netdev;
      int err;
      struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum);
      bool kick = !skb->xmit_more;
      bool use_napi = sq->napi.weight;
  +    /* If VF is present and up then redirect packets
+     * called with rcu_read_lock_bh
+     */
+    vf_netdev = rcu_dereference_bh(vi->vf_netdev);
+    if (vf_netdev && netif_running(vf_netdev) &&
+        !netpoll_tx_running(dev) &&
+        is_unicast_ether_addr(eth_hdr(skb)->h_dest))
+        return virtnet_vf_xmit(dev, vf_netdev, skb);

A question here.

If I read the code correctly, all features were validated against virtio instead VF before transmitting. This assumes VF's feature is a superset of virtio, does this really work? Do we need to sanitize the feature before joining? (e.g at last NETIF_R_GSO_ROBUST needs to be removed).

Actually, virtnet_vf_xmit() calls dev_queue_xmit() after updating skb->dev to vf netdev. So the features get validated against VF features and the right tx queue is selected
before the real transmit.

I see, the the packet will go through qdiscs twice which is suboptimal. And the device may lose some ability of VF like tunnel GSO.



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