eth: Declare an optimized compare_ether_addr_64bits() function

Linus mentioned we could try to perform long word operations, even
on potentially unaligned addresses, on x86 at least. David mentioned
the HAVE_EFFICIENT_UNALIGNED_ACCESS test to handle this on all
arches that have efficient unailgned accesses.

I tried this idea and got nice assembly on 32 bits:

158:   33 82 38 01 00 00       xor    0x138(%edx),%eax
15e:   33 8a 34 01 00 00       xor    0x134(%edx),%ecx
164:   c1 e0 10                shl    $0x10,%eax
167:   09 c1                   or     %eax,%ecx
169:   74 0b                   je     176 <eth_type_trans+0x87>

And very nice assembly on 64 bits of course (one xor, one shl)

Nice oprofile improvement in eth_type_trans(), 0.17 % instead of 0.41 %,
expected since we remove 8 instructions on a fast path.

This patch implements a compare_ether_addr_64bits() function, that
uses the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS ifdef to efficiently
perform the 6 bytes comparison on all capable arches.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index a87a171d9914..280352aba403 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -165,8 +165,8 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
         skb_pull(skb, ETH_HLEN);
         eth = eth_hdr(skb);
 
-        if (is_multicast_ether_addr(eth->h_dest)) {
-                if (!compare_ether_addr(eth->h_dest, dev->broadcast))
+        if (unlikely(is_multicast_ether_addr(eth->h_dest))) {
+                if (!compare_ether_addr_64bits(eth->h_dest, dev->broadcast))
                         skb->pkt_type = PACKET_BROADCAST;
                 else
                         skb->pkt_type = PACKET_MULTICAST;
@@ -181,7 +181,7 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
          */
 
         else if (1 /*dev->flags&IFF_PROMISC */ ) {
-                if (unlikely(compare_ether_addr(eth->h_dest, dev->dev_addr)))
+                if (unlikely(compare_ether_addr_64bits(eth->h_dest, dev->dev_addr)))
                         skb->pkt_type = PACKET_OTHERHOST;
         }