From: David S. Miller <davem@davemloft.net>
Date: Sun, 3 May 2009 21:43:10 +0000 (-0700)
Subject: net: Avoid modulus in skb_tx_hash() for forwarding case.
X-Git-Tag: v2.6.31-rc1~330^2~489
X-Git-Url: https://openfabrics.org/gitweb/?a=commitdiff_plain;h=513de11bba246b7a67df4c314d9fc936b6a75d0e;p=~emulex%2Finfiniband.git

net: Avoid modulus in skb_tx_hash() for forwarding case.

Based almost entirely upon a patch by Eric Dumazet.

The common case is to have num-tx-queues <= num_rx_queues
and even if num_tx_queues is larger it will not be significantly
larger.

Therefore, a subtraction loop is always going to be faster than
modulus.

Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/core/dev.c b/net/core/dev.c
index 81442957c5c..3c8073fe970 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1735,8 +1735,12 @@ u16 skb_tx_hash(const struct net_device *dev, const struct sk_buff *skb)
 {
 	u32 hash;
 
-	if (skb_rx_queue_recorded(skb))
-		return skb_get_rx_queue(skb) % dev->real_num_tx_queues;
+	if (skb_rx_queue_recorded(skb)) {
+		hash = skb_get_rx_queue(skb);
+		while (unlikely (hash >= dev->real_num_tx_queues))
+			hash -= dev->real_num_tx_queues;
+		return hash;
+	}
 
 	if (skb->sk && skb->sk->sk_hash)
 		hash = skb->sk->sk_hash;