• Jesper Dangaard Brouer's avatar
    xdp: separate xdp_redirect tracepoint in error case · f5836ca5
    Jesper Dangaard Brouer authored
    There is a need to separate the xdp_redirect tracepoint into two
    tracepoints, for separating the error case from the normal forward
    case.
    
    Due to the extreme speeds XDP is operating at, loading a tracepoint
    have a measurable impact.  Single core XDP REDIRECT (ethtool tuned
    rx-usecs 25) can do 13.7 Mpps forwarding, but loading a simple
    bpf_prog at the tracepoint (with a return 0) reduce perf to 10.2 Mpps
    (CPU E5-1650 v4 @ 3.60GHz, driver: ixgbe)
    
    The overhead of loading a bpf-based tracepoint can be calculated to
    cost 25 nanosec ((1/13782002-1/10267937)*10^9 = -24.83 ns).
    
    Using perf record on the tracepoint event, with a non-matching --filter
    expression, the overhead is much larger. Performance drops to 8.3 Mpps,
    cost 48 nanosec ((1/13782002-1/8312497)*10^9 = -47.74))
    
    Having a separate tracepoint for err cases, which should be less
    frequent, allow running a continuous monitor for errors while not
    affecting the redirect forward performance (this have also been
    verified by measurements).
    Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
    Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    f5836ca5
xdp.h 2.95 KB