net: Optimize skb_tx_hash() by eliminating a comparison

Optimize skb_tx_hash() by eliminating a comparison that executes for
every packet. skb_tx_hashrnd initialization is moved to a later part of
the startup sequence, namely after the "random" driver is initialized.

Rebooted the system three times and verified that the code generates
different random numbers each time.
Signed-off-by: NKrishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1745,17 +1745,11 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 }
 
 static u32 skb_tx_hashrnd;
-static int skb_tx_hashrnd_initialized = 0;
 
 static u16 skb_tx_hash(struct net_device *dev, struct sk_buff *skb)
 {
 	u32 hash;
 
-	if (unlikely(!skb_tx_hashrnd_initialized)) {
-		get_random_bytes(&skb_tx_hashrnd, 4);
-		skb_tx_hashrnd_initialized = 1;
-	}
-
 	if (skb_rx_queue_recorded(skb)) {
 		hash = skb_get_rx_queue(skb);
 	} else if (skb->sk && skb->sk->sk_hash) {
@@ -5291,6 +5285,14 @@ static int __init net_dev_init(void)
 
 subsys_initcall(net_dev_init);
 
+static int __init initialize_hashrnd(void)
+{
+	get_random_bytes(&skb_tx_hashrnd, sizeof(skb_tx_hashrnd));
+	return 0;
+}
+
+late_initcall_sync(initialize_hashrnd);
+
 EXPORT_SYMBOL(__dev_get_by_index);
 EXPORT_SYMBOL(__dev_get_by_name);
 EXPORT_SYMBOL(__dev_remove_pack);