• Jesper Dangaard Brouer's avatar
    net: help compiler generate better code in eth_get_headlen · 8a4683a5
    Jesper Dangaard Brouer authored
    Noticed that the compiler (gcc version 4.8.5 20150623 (Red Hat 4.8.5-4) (GCC))
    generated suboptimal assembler code in eth_get_headlen().
    This early return coding style is usually not an issue, on super scalar CPUs,
    but the compiler choose to put the return statement after this very unlikely
    branch, thus creating larger jump down to the likely code path.
    Performance wise, I could measure slightly less L1-icache-load-misses
    and less branch-misses, and an improvement of 1 nanosec with an IP-forwarding
    use-case with 257 bytes packets with ixgbe (CPU i7-4790K @ 4.00GHz).
    Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>