[PATCH net-next 0/8] tcp: default RACK loss recovery

[Yuchung Cheng <ycheng@google.com>]

This patch set implements the features correspond to the
draft-ietf-tcpm-rack-03 version of the RACK draft.
https://datatracker.ietf.org/meeting/101/materials/slides-101-tcpm-update-on-tcp-rack-00

1. SACK: implement equivalent DUPACK threshold heuristic in RACK to
   replace existing RFC6675 recovery (tcp_mark_head_lost).

2. Non-SACK: simplify RFC6582 NewReno implementation

3. RTO: apply RACK's time-based approach to avoid spuriouly
   marking very recently sent packets lost.

4. with (1)(2)(3), make RACK the exclusive fast recovery mechanism to
   mark losses based on time on S/ACK. Tail loss probe and F-RTO remain
   enabled by default as complementary mechanisms to send probes in
   CA_Open and CA_Loss states. The probes would solicit S/ACKs to trigger
   RACK time-based loss detection.

All Google web and internal servers have been running RACK-only mode
(4) for a while now. a/b experiments indicate RACK/TLP on average
reduces recovery latency by 10% compared to RFC6675. RFC6675
is default-off now but can be enabled by disabling RACK (sysctl
net.ipv4.tcp_recovery=0) for unseen issues.

Yuchung Cheng (8):
  tcp: support DUPACK threshold in RACK
  tcp: disable RFC6675 loss detection
  tcp: simpler NewReno implementation
  tcp: account lost retransmit after timeout
  tcp: new helper tcp_timeout_mark_lost
  tcp: separate loss marking and state update on RTO
  tcp: new helper tcp_rack_skb_timeout
  tcp: don't mark recently sent packets lost on RTO

 Documentation/networking/ip-sysctl.txt |  4 +-
 include/net/tcp.h                      |  5 ++
 net/ipv4/tcp_input.c                   | 99 ++++++++++++++------------
 net/ipv4/tcp_recovery.c                | 80 ++++++++++++++++-----
 4 files changed, 124 insertions(+), 64 deletions(-)

-- 
2.17.0.441.gb46fe60e1d-goog