• Alan Maguire's avatar
    selftests/bpf: measure RTT from xdp using xdping · cd538502
    Alan Maguire authored
    xdping allows us to get latency estimates from XDP.  Output looks
    like this:
    
    ./xdping -I eth4 192.168.55.8
    Setting up XDP for eth4, please wait...
    XDP setup disrupts network connectivity, hit Ctrl+C to quit
    
    Normal ping RTT data
    [Ignore final RTT; it is distorted by XDP using the reply]
    PING 192.168.55.8 (192.168.55.8) from 192.168.55.7 eth4: 56(84) bytes of data.
    64 bytes from 192.168.55.8: icmp_seq=1 ttl=64 time=0.302 ms
    64 bytes from 192.168.55.8: icmp_seq=2 ttl=64 time=0.208 ms
    64 bytes from 192.168.55.8: icmp_seq=3 ttl=64 time=0.163 ms
    64 bytes from 192.168.55.8: icmp_seq=8 ttl=64 time=0.275 ms
    
    4 packets transmitted, 4 received, 0% packet loss, time 3079ms
    rtt min/avg/max/mdev = 0.163/0.237/0.302/0.054 ms
    
    XDP RTT data:
    64 bytes from 192.168.55.8: icmp_seq=5 ttl=64 time=0.02808 ms
    64 bytes from 192.168.55.8: icmp_seq=6 ttl=64 time=0.02804 ms
    64 bytes from 192.168.55.8: icmp_seq=7 ttl=64 time=0.02815 ms
    64 bytes from 192.168.55.8: icmp_seq=8 ttl=64 time=0.02805 ms
    
    The xdping program loads the associated xdping_kern.o BPF program
    and attaches it to the specified interface.  If run in client
    mode (the default), it will add a map entry keyed by the
    target IP address; this map will store RTT measurements, current
    sequence number etc.  Finally in client mode the ping command
    is executed, and the xdping BPF program will use the last ICMP
    reply, reformulate it as an ICMP request with the next sequence
    number and XDP_TX it.  After the reply to that request is received
    we can measure RTT and repeat until the desired number of
    measurements is made.  This is why the sequence numbers in the
    normal ping are 1, 2, 3 and 8.  We XDP_TX a modified version
    of ICMP reply 4 and keep doing this until we get the 4 replies
    we need; hence the networking stack only sees reply 8, where
    we have XDP_PASSed it upstream since we are done.
    
    In server mode (-s), xdping simply takes ICMP requests and replies
    to them in XDP rather than passing the request up to the networking
    stack.  No map entry is required.
    
    xdping can be run in native XDP mode (the default, or specified
    via -N) or in skb mode (-S).
    
    A test program test_xdping.sh exercises some of these options.
    
    Note that native XDP does not seem to XDP_TX for veths, hence -N
    is not tested.  Looking at the code, it looks like XDP_TX is
    supported so I'm not sure if that's expected.  Running xdping in
    native mode for ixgbe as both client and server works fine.
    
    Changes since v4
    
    - close fds on cleanup (Song Liu)
    
    Changes since v3
    
    - fixed seq to be __be16 (Song Liu)
    - fixed fd checks in xdping.c (Song Liu)
    
    Changes since v2
    
    - updated commit message to explain why seq number of last
      ICMP reply is 8 not 4 (Song Liu)
    - updated types of seq number, raddr and eliminated csum variable
      in xdpclient/xdpserver functions as it was not needed (Song Liu)
    - added XDPING_DEFAULT_COUNT definition and usage specification of
      default/max counts (Song Liu)
    
    Changes since v1
     - moved from RFC to PATCH
     - removed unused variable in ipv4_csum() (Song Liu)
     - refactored ICMP checks into icmp_check() function called by client
       and server programs and reworked client and server programs due
       to lack of shared code (Song Liu)
     - added checks to ensure that SKB and native mode are not requested
       together (Song Liu)
    Signed-off-by: default avatarAlan Maguire <alan.maguire@oracle.com>
    Acked-by: default avatarSong Liu <songliubraving@fb.com>
    Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
    cd538502
xdping.c 5.8 KB