aoe: print warning regarding a common reason for dropped transmits

Dropped transmits are not common, but when they do occur, increasing
the transmit queue length often helps.

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/aoe/aoenet.c

@@ -52,13 +52,18 @@ static struct sk_buff_head skbtxq;
 
 /* enters with txlock held */
 static int
-tx(void)
+tx(void) __must_hold(&txlock)
 {
 	struct sk_buff *skb;
+	struct net_device *ifp;
 
 	while ((skb = skb_dequeue(&skbtxq))) {
 		spin_unlock_irq(&txlock);
-		dev_queue_xmit(skb);
+		ifp = skb->dev;
+		if (dev_queue_xmit(skb) == NET_XMIT_DROP && net_ratelimit())
+			pr_warn("aoe: packet could not be sent on %s.  %s\n",
+				ifp ? ifp->name : "netif",
+				"consider increasing tx_queue_len");
 		spin_lock_irq(&txlock);
 	}
 	return 0;