From: Yuchung Cheng <ych...@google.com> Date: Wed, 30 Mar 2016 14:54:20 -0700
> 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: Matt Mathis <mattmat...@google.com> > Signed-off-by: Neal Cardwell <ncardw...@google.com> > Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com> > Signed-off-by: Yuchung Cheng <ych...@google.com> Applied, thanks.
