• Jon Maloy's avatar
    tipc: introduce variable window congestion control · 16ad3f40
    Jon Maloy authored
    We introduce a simple variable window congestion control for links.
    The algorithm is inspired by the Reno algorithm, covering both 'slow
    start', 'congestion avoidance', and 'fast recovery' modes.
    
    - We introduce hard lower and upper window limits per link, still
      different and configurable per bearer type.
    
    - We introduce a 'slow start theshold' variable, initially set to
      the maximum window size.
    
    - We let a link start at the minimum congestion window, i.e. in slow
      start mode, and then let is grow rapidly (+1 per rceived ACK) until
      it reaches the slow start threshold and enters congestion avoidance
      mode.
    
    - In congestion avoidance mode we increment the congestion window for
      each window-size number of acked packets, up to a possible maximum
      equal to the configured maximum window.
    
    - For each non-duplicate NACK received, we drop back to fast recovery
      mode, by setting the both the slow start threshold to and the
      congestion window to (current_congestion_window / 2).
    
    - If the timeout handler finds that the transmit queue has not moved
      since the previous timeout, it drops the link back to slow start
      and forces a probe containing the last sent sequence number to the
      sent to the peer, so that this can discover the stale situation.
    
    This change does in reality have effect only on unicast ethernet
    transport, as we have seen that there is no room whatsoever for
    increasing the window max size for the UDP bearer.
    For now, we also choose to keep the limits for the broadcast link
    unchanged and equal.
    
    This algorithm seems to give a 50-100% throughput improvement for
    messages larger than MTU.
    Suggested-by: default avatarXin Long <lucien.xin@gmail.com>
    Acked-by: default avatarYing Xue <ying.xue@windriver.com>
    Signed-off-by: default avatarJon Maloy <jon.maloy@ericsson.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    16ad3f40
bcast.c 21.5 KB