• Eric Dumazet's avatar
    tcp: introduce TCPSpuriousRtxHostQueues SNMP counter · 0e280af0
    Eric Dumazet authored
    Host queues (Qdisc + NIC) can hold packets so long that TCP can
    eventually retransmit a packet before the first transmit even left
    the host.
    
    Its not clear right now if we could avoid this in the first place :
    
    - We could arm RTO timer not at the time we enqueue packets, but
      at the time we TX complete them (tcp_wfree())
    
    - Cancel the sending of the new copy of the packet if prior one
      is still in queue.
    
    This patch adds instrumentation so that we can at least see how
    often this problem happens.
    
    TCPSpuriousRtxHostQueues SNMP counter is incremented every time
    we detect the fast clone is not yet freed in tcp_transmit_skb()
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Cc: Yuchung Cheng <ycheng@google.com>
    Cc: Neal Cardwell <ncardwell@google.com>
    Cc: Tom Herbert <therbert@google.com>
    Cc: Willem de Bruijn <willemb@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    0e280af0
proc.c 18.5 KB