From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Wed, 27 May 2009 15:31:07 +1000
Subject: [net] gro: Optimise Ethernet header comparison
Message-id: E1M9BjH-0002AD-KO@gondolin.me.apana.org.au
O-Subject: [PATCH 3/17] gro: Optimise Ethernet header comparison
Bugzilla: 499347
RH-Acked-by: David Miller <davem@redhat.com>
RH-Acked-by: Neil Horman <nhorman@redhat.com>
RH-Acked-by: Thomas Graf <tgraf@redhat.com>

RHEL5 bugzilla #499347

gro: Optimise Ethernet header comparison

This patch optimises the Ethernet header comparison to use 2-byte
and 4-byte xors instead of memcmp.  In order to facilitate this,
the actual comparison is now carried out by the callers of the
shared dev_gro_receive function.

This has a significant impact when receiving 1500B packets through
10GbE.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
index 745c988..d3c6c94 100644
--- a/include/linux/etherdevice.h
+++ b/include/linux/etherdevice.h
@@ -128,4 +128,25 @@ static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2)
 }
 #endif	/* __KERNEL__ */
 
+/**
+ * compare_ether_header - Compare two Ethernet headers
+ * @a: Pointer to Ethernet header
+ * @b: Pointer to Ethernet header
+ *
+ * Compare two ethernet headers, returns 0 if equal.
+ * This assumes that the network header (i.e., IP header) is 4-byte
+ * aligned OR the platform can handle unaligned access.  This is the
+ * case for all packets coming into netif_receive_skb or similar
+ * entry points.
+ */
+
+static inline int compare_ether_header(const void *a, const void *b)
+{
+	u32 *a32 = (u32 *)((u8 *)a + 2);
+	u32 *b32 = (u32 *)((u8 *)b + 2);
+
+	return (*(u16 *)a ^ *(u16 *)b) | (a32[0] ^ b32[0]) |
+	       (a32[1] ^ b32[1]) | (a32[2] ^ b32[2]);
+}
+
 #endif	/* _LINUX_ETHERDEVICE_H */