Linus Torvalds a écrit : > > On Tue, 18 Nov 2008, Eric Dumazet wrote: >>> * >>> * Compare two ethernet addresses, returns 0 if equal >>> */ >>> static inline unsigned compare_ether_addr(const u8 *addr1, const u8 *addr2) >>> { >>> const u16 *a = (const u16 *) addr1; >>> const u16 *b = (const u16 *) addr2; >>> >>> BUILD_BUG_ON(ETH_ALEN != 6); >>> return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])) != 0; > > Btw, at least on some Intel CPU's, it would be faster to do this as a > 32-bit xor and a 16-bit xor. And if we can know that there is always 2 > bytes at the end (because of how the thing was allocated), it's faster > still to do it as a 64-bit xor and a mask. > > And that's true even if the addresses are only 2-byte aligned. > Yes, this is allowed, we always have at least 8 bytes for both arrays, when called from eth_type_trans() at least. 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 And very nice assembly on 64 bits of course (one xor, one shl) About alignments, we have aligned addr2, but not addr1 Nice oprofile improvement in eth_type_trans(), 0.17 % instead of 0.41 % opreport -l vmlinux | grep eth_type_trans 38797 0.1710 eth_type_trans [PATCH] 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. This patch implements a compare_ether_addr_64bits() function, that handles the case of x86 cpus, but might be used on other arches as well. Signed-off-by: Eric Dumazet ---