Merge branch 'iocb' into for-davem

[deliverable/linux.git] / drivers / net / virtio_net.c

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index a829930dac150e2910629f4d918b3dca3b493e8a..63c7810e1545a357eda7578af862ed18322de933 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -939,11 +939,15 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
        skb_orphan(skb);
        nf_reset(skb);
 
-       /* It is better to stop queue if running out of space
-        * instead of forcing queuing layer to requeue the skb
-        * by returning TX_BUSY (and cause a BUG message).
-        * Since most packets only take 1 or 2 ring slots
-        * this means 16 slots are typically wasted.
+       /* If running out of space, stop queue to avoid getting packets that we
+        * are then unable to transmit.
+        * An alternative would be to force queuing layer to requeue the skb by
+        * returning NETDEV_TX_BUSY. However, NETDEV_TX_BUSY should not be
+        * returned in a normal path of operation: it means that driver is not
+        * maintaining the TX queue stop/start state properly, and causes
+        * the stack to do a non-trivial amount of useless work.
+        * Since most packets only take 1 or 2 ring slots, stopping the queue
+        * early means 16 slots are typically wasted.
         */
        if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
                netif_stop_subqueue(dev, qnum);