The patch set enables RACK loss detection (draft-ietf-tcpm-rack-01) to trigger fast recovery with a reordering timer.
Previously RACK has been running in auxiliary mode where it is used to detect packet losses once the recovery has triggered by other algorithms (e.g., FACK). By inspecting packet timestamps, RACK can start ACK-driven repairs timely. A few similar heuristics are no longer needed and are either removed or disabled to reduce the complexity of the Linux TCP loss recovery engine: 1. FACK (Forward Acknowledgement) 2. Early Retransmit (RFC5827) 3. thin_dupack (fast recovery on single DUPACK for thin-streams) 4. NCR (Non-Congestion Robustness RFC4653) (RFC4653) 5. Forward Retransmit After this change, Linux's loss recovery algorithms consist of 1. Conventional DUPACK threshold approach (RFC6675) 2. RACK and Tail Loss Probe (draft-ietf-tcpm-rack-01) 3. RTO plus F-RTO extension (RFC5682) The patch set has been tested on Google servers extensively and presented in several IETF meetings. The data suggests that RACK successfully improves recovery performance: https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-draft-ietf-tcpm-rack-01.pdf https://www.ietf.org/proceedings/96/slides/slides-96-tcpm-3.pdf Yuchung Cheng (13): tcp: new helper function for RACK loss detection tcp: new helper for RACK to detect loss tcp: record most recent RTT in RACK loss detection tcp: add reordering timer in RACK loss detection tcp: use sequence to break TS ties for RACK loss detection tcp: check undo conditions before detecting losses tcp: enable RACK loss detection to trigger recovery tcp: extend F-RTO to catch more spurious timeouts tcp: remove forward retransmit feature tcp: remove early retransmit tcp: remove RFC4653 NCR tcp: remove thin_dupack feature tcp: disable fack by default Documentation/networking/ip-sysctl.txt | 31 +---- include/linux/tcp.h | 8 +- include/net/inet_connection_sock.h | 4 +- include/net/tcp.h | 40 ++---- net/ipv4/inet_diag.c | 2 +- net/ipv4/sysctl_net_ipv4.c | 7 -- net/ipv4/tcp.c | 9 +- net/ipv4/tcp_input.c | 224 +++++++++++++-------------------- net/ipv4/tcp_ipv4.c | 2 +- net/ipv4/tcp_metrics.c | 1 - net/ipv4/tcp_minisocks.c | 1 - net/ipv4/tcp_output.c | 75 ++--------- net/ipv4/tcp_recovery.c | 148 ++++++++++++++++------ net/ipv4/tcp_timer.c | 4 +- net/ipv6/tcp_ipv6.c | 2 +- 15 files changed, 237 insertions(+), 321 deletions(-) -- 2.11.0.483.g087da7b7c-goog
