RH6: hv_netvsc: Fix for packet drop during xmit from VF

Data transmission from VF txq will cause packet drop when queue is stopped
or frozen. In such case sythetic datapath should be used to continue tx.
This patch also improves the performance when the number of connection
increases.

hv-rhel6.x/hv/netvsc_drv.c

@@ -253,19 +253,14 @@ static u16 netvsc_select_queue(struct net_device *ndev, struct sk_buff *skb)
 {
 	struct net_device_context *ndc = netdev_priv(ndev);
 	struct net_device *vf_netdev;
-	u16 txq;
+	u16 txq = 0;
 
 	rcu_read_lock();
 	vf_netdev = rcu_dereference(ndc->vf_netdev);
 	if (vf_netdev) {
 		const struct net_device_ops *vf_ops = vf_netdev->netdev_ops;
-
 		if (vf_ops->ndo_select_queue)
 			txq = vf_ops->ndo_select_queue(vf_netdev, skb);
-		else
-			txq = 0;
-
-		qdisc_skb_cb(skb)->slave_dev_queue_mapping = txq;
 	} else {
 		txq = netvsc_pick_tx(ndev, skb);
 	}
@@ -278,6 +273,21 @@ static u16 netvsc_select_queue(struct net_device *ndev, struct sk_buff *skb)
 }
 
 
+static int netvsc_txq_stopped_or_frozen(struct net_device *vf_netdev, struct sk_buff *skb)
+{
+	u16 txq_index = 0;
+	struct netdev_queue *txq;
+	const struct net_device_ops *vf_ops = vf_netdev->netdev_ops;
+
+	if (vf_ops->ndo_select_queue)
+		txq_index = vf_ops->ndo_select_queue(vf_netdev, skb);
+
+	qdisc_skb_cb(skb)->slave_dev_queue_mapping = txq_index;
+	txq = netdev_get_tx_queue(vf_netdev, txq_index);
+
+	return (netif_tx_queue_stopped(txq) || netif_tx_queue_frozen(txq));
+}
+
 /* Send skb on the slave VF device. */
 static int netvsc_vf_xmit(struct net_device *net, struct net_device *vf_netdev,
 		  struct sk_buff *skb)
@@ -567,8 +577,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	 */
 	vf_netdev = rcu_dereference_bh(net_device_ctx->vf_netdev);
 	if (vf_netdev && netif_running(vf_netdev) &&
-		!netpoll_tx_running(net) && !in_serving_softirq() &&
-		!netif_queue_stopped(vf_netdev)) {
+		!netpoll_tx_running(net) && !netvsc_txq_stopped_or_frozen(vf_netdev, skb)) {
 		return netvsc_vf_xmit(net, vf_netdev, skb);
 	}
 #endif