• Neil Horman's avatar
    net: implement emergency route cache rebulds when gc_elasticity is exceeded · 1080d709
    Neil Horman authored
    This is a patch to provide on demand route cache rebuilding.  Currently, our
    route cache is rebulid periodically regardless of need.  This introduced
    unneeded periodic latency.  This patch offers a better approach.  Using code
    provided by Eric Dumazet, we compute the standard deviation of the average hash
    bucket chain length while running rt_check_expire.  Should any given chain
    length grow to larger that average plus 4 standard deviations, we trigger an
    emergency hash table rebuild for that net namespace.  This allows for the common
    case in which chains are well behaved and do not grow unevenly to not incur any
    latency at all, while those systems (which may be being maliciously attacked),
    only rebuild when the attack is detected.  This patch take 2 other factors into
    account:
    1) chains with multiple entries that differ by attributes that do not affect the
    hash value are only counted once, so as not to unduly bias system to rebuilding
    if features like QOS are heavily used
    2) if rebuilding crosses a certain threshold (which is adjustable via the added
    sysctl in this patch), route caching is disabled entirely for that net
    namespace, since constant rebuilding is less efficient that no caching at all
    
    Tested successfully by me.
    Signed-off-by: default avatarNeil Horman <nhorman@tuxdriver.com>
    Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    1080d709
sysctl_net_ipv4.c 21.2 KB