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  1. Apr 03, 2016
    • Yuchung Cheng's avatar
      tcp: remove cwnd moderation after recovery · 23492623
      Yuchung Cheng authored
      
      
      For non-SACK connections, cwnd is lowered to inflight plus 3 packets
      when the recovery ends. This is an optional feature in the NewReno
      RFC 2582 to reduce the potential burst when cwnd is "re-opened"
      after recovery and inflight is low.
      
      This feature is questionably effective because of PRR: when
      the recovery ends (i.e., snd_una == high_seq) NewReno holds the
      CA_Recovery state for another round trip to prevent false fast
      retransmits. But if the inflight is low, PRR will overwrite the
      moderated cwnd in tcp_cwnd_reduction() later regardlessly. So if a
      receiver responds bogus ACKs (i.e., acking future data) to speed up
      transfer after recovery, it can only induce a burst up to a window
      worth of data packets by acking up to SND.NXT. A restart from (short)
      idle or receiving streched ACKs can both cause such bursts as well.
      
      On the other hand, if the recovery ends because the sender
      detects the losses were spurious (e.g., reordering). This feature
      unconditionally lowers a reverted cwnd even though nothing
      was lost.
      
      By principle loss recovery module should not update cwnd. Further
      pacing is much more effective to reduce burst. Hence this patch
      removes the cwnd moderation feature.
      
      v2 changes: revised commit message on bogus ACKs and burst, and
                  missing signature
      
      Signed-off-by: default avatarMatt Mathis <mattmathis@google.com>
      Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
      Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
      Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      23492623
  2. Apr 02, 2016
  3. Apr 01, 2016