IW10 broken when not doing ABC

[Scheffenegger, Richard]

Hi,

Just added this comment to D18940. Would appreciate it, if someone other than me can confirm this behavior, which may have been present for some time already.

Also, I found some other oddities around ABC calculation in modular congestion control, but want to discuss them internally first; if anyone is having time and wants to also investigate, please PM.

Best regards,
   Richard



Subject: [Differential] D18940: Consolidate Initial Window calculations

  I was just starting to validate something around RTO, and found, that the effective IW is now actually 11 SMSS, not 10 MSS, when NOT doing ABC (net.inet.tcp.rfc3465=0).

  I suspect, the final ACK of the 3WHS is already processed in the normal ACK path, increasing cwnd at that point by one MSS.

  Here is the corresponding Packetdrill script (named for what I wanted to validate, before hitting this).
  F4175462: newreno-slowstart-after-rto.pkt <https://reviews.freebsd.org/F4175462>

REPOSITORY
  rS FreeBSD src repository

CHANGES SINCE LAST ACTION
  https://reviews.freebsd.org/D18940/new/

REVISION DETAIL
  https://reviews.freebsd.org/D18940

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To: rscheff_gmx.at, #transport, tuexen
Cc: imp, thj, rscheff_gmx.at