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Commit 1f87e235 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 70eb1bfd

include/linux/etherdevice.h

+42 −0
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ 
#include <linux/if_ether.h>

#include <linux/netdevice.h>

#include <linux/random.h>

#include <asm/unaligned.h>



#ifdef __KERNEL__

extern __be16		eth_type_trans(struct sk_buff *skb, struct net_device *dev);
@@ -140,6 +141,47 @@ static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2) 
	BUILD_BUG_ON(ETH_ALEN != 6);

	return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])) != 0;

}



static inline unsigned long zap_last_2bytes(unsigned long value)

{

#ifdef __BIG_ENDIAN

	return value >> 16;

#else

	return value << 16;

#endif

}



/**

 * compare_ether_addr_64bits - Compare two Ethernet addresses

 * @addr1: Pointer to an array of 8 bytes

 * @addr2: Pointer to an other array of 8 bytes

 *

 * Compare two ethernet addresses, returns 0 if equal.

 * Same result than "memcmp(addr1, addr2, ETH_ALEN)" but without conditional

 * branches, and possibly long word memory accesses on CPU allowing cheap

 * unaligned memory reads.

 * arrays = { byte1, byte2, byte3, byte4, byte6, byte7, pad1, pad2}

 *

 * Please note that alignment of addr1 & addr2 is only guaranted to be 16 bits.

 */



static inline unsigned compare_ether_addr_64bits(const u8 addr1[6+2],

						 const u8 addr2[6+2])

{

#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

	unsigned long fold = ((*(unsigned long *)addr1) ^

			      (*(unsigned long *)addr2));



	if (sizeof(fold) == 8)

		return zap_last_2bytes(fold) != 0;



	fold |= zap_last_2bytes((*(unsigned long *)(addr1 + 4)) ^

				(*(unsigned long *)(addr2 + 4)));

	return fold != 0;

#else

	return compare_ether_addr(addr1, addr2);

#endif

}

#endif	/* __KERNEL__ */



#endif	/* _LINUX_ETHERDEVICE_H */

net/ethernet/eth.c

+3 −3
Original line number Diff line number Diff line
@@ -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;

	}