[NET]: Slightly optimize ethernet address comparison.
David S. Miller [Tue, 27 Sep 2005 23:03:05 +0000 (16:03 -0700)]
We know the thing is at least 2-byte aligned, so take
advantage of that instead of invoking memcmp() which
results in truly horrifically inefficient code because
it can't assume anything about alignment.

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

net/ethernet/eth.c

index 87a052a..8b299cc 100644 (file)
@@ -146,6 +146,19 @@ int eth_rebuild_header(struct sk_buff *skb)
        return 0;
 }
 
+static inline unsigned int compare_eth_addr(const unsigned char *__a, const unsigned char *__b)
+{
+       const unsigned short *dest = (unsigned short *) __a;
+       const unsigned short *devaddr = (unsigned short *) __b;
+       unsigned int res;
+
+       BUILD_BUG_ON(ETH_ALEN != 6);
+       res = ((dest[0] ^ devaddr[0]) |
+              (dest[1] ^ devaddr[1]) |
+              (dest[2] ^ devaddr[2])) != 0;
+
+       return res;
+}
 
 /*
  *     Determine the packet's protocol ID. The rule here is that we 
@@ -158,16 +171,15 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
        struct ethhdr *eth;
        unsigned char *rawp;
        
-       skb->mac.raw=skb->data;
+       skb->mac.raw = skb->data;
        skb_pull(skb,ETH_HLEN);
        eth = eth_hdr(skb);
        
-       if(*eth->h_dest&1)
-       {
-               if(memcmp(eth->h_dest,dev->broadcast, ETH_ALEN)==0)
-                       skb->pkt_type=PACKET_BROADCAST;
+       if (*eth->h_dest&1) {
+               if (!compare_eth_addr(eth->h_dest, dev->broadcast))
+                       skb->pkt_type = PACKET_BROADCAST;
                else
-                       skb->pkt_type=PACKET_MULTICAST;
+                       skb->pkt_type = PACKET_MULTICAST;
        }
        
        /*
@@ -178,10 +190,9 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
         *      seems to set IFF_PROMISC.
         */
         
-       else if(1 /*dev->flags&IFF_PROMISC*/)
-       {
-               if(memcmp(eth->h_dest,dev->dev_addr, ETH_ALEN))
-                       skb->pkt_type=PACKET_OTHERHOST;
+       else if(1 /*dev->flags&IFF_PROMISC*/) {
+               if (unlikely(!compare_eth_addr(eth->h_dest, dev->dev_addr)))
+                       skb->pkt_type = PACKET_OTHERHOST;
        }
        
        if (ntohs(eth->h_proto) >= 1536)