• Eric Dumazet's avatar
    eth: Declare an optimized compare_ether_addr_64bits() function · 1f87e235
    Eric Dumazet authored
    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>
    1f87e235
eth.c 10.9 KB