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: Krishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/dev.c b/net/core/dev.c
index d393fc9..5493394 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1745,17 +1745,11 @@ out_kfree_skb:
 }
 
 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 @@ out:
 
 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);