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>
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index a87a171..280352a 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -165,8 +165,8 @@
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 @@
*/
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;
}