• Tom Herbert's avatar
    net: Save TX flow hash in sock and set in skbuf on xmit · b73c3d0e
    Tom Herbert authored
    For a connected socket we can precompute the flow hash for setting
    in skb->hash on output. This is a performance advantage over
    calculating the skb->hash for every packet on the connection. The
    computation is done using the common hash algorithm to be consistent
    with computations done for packets of the connection in other states
    where thers is no socket (e.g. time-wait, syn-recv, syn-cookies).
    
    This patch adds sk_txhash to the sock structure. inet_set_txhash and
    ip6_set_txhash functions are added which are called from points in
    TCP and UDP where socket moves to established state.
    
    skb_set_hash_from_sk is a function which sets skb->hash from the
    sock txhash value. This is called in UDP and TCP transmit path when
    transmitting within the context of a socket.
    
    Tested: ran super_netperf with 200 TCP_RR streams over a vxlan
    interface (in this case skb_get_hash called on every TX packet to
    create a UDP source port).
    
    Before fix:
    
      95.02% CPU utilization
      154/256/505 90/95/99% latencies
      1.13042e+06 tps
    
      Time in functions:
        0.28% skb_flow_dissect
        0.21% __skb_get_hash
    
    After fix:
    
      94.95% CPU utilization
      156/254/485 90/95/99% latencies
      1.15447e+06
    
      Neither __skb_get_hash nor skb_flow_dissect appear in perf
    Signed-off-by: default avatarTom Herbert <therbert@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    b73c3d0e
ip.h 15.4 KB