Merge branch 'tcp-default-RACK-loss-recovery'
Yuchung Cheng says:
====================
tcp: default RACK loss recovery
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.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
