[PATCH v3 net-next 0/2] tcp: Redundant Data Bundling (RDB)

Bendik Rønning Opstad
2016-02-02T19:24:08Z

Redundant Data Bundling (RDB) is a mechanism for TCP aimed at reducing
the latency for applications sending time-dependent data.
Latency-sensitive applications or services, such as online games and
remote desktop, produce traffic with thin-stream characteristics,
characterized by small packets and a relatively high ITT. By bundling
already sent data in packets with new data, RDB alleviates head-of-line
blocking by reducing the need to retransmit data segments when packets
are lost. RDB is a continuation on the work on latency improvements for
TCP in Linux, previously resulting in two thin-stream mechanisms in the
Linux kernel
(https://github.com/torvalds/linux/blob/master/Documentation/networking/tcp-thin.txt).

The RDB implementation has been thoroughly tested, and shows
significant latency reductions when packet loss occurs[1]. The tests
show that, by imposing restrictions on the bundling rate, it can be
made not to negatively affect competing traffic in an unfair manner.

Note: Current patch set depends on the patch "tcp: refactor struct tcp_skb_cb"
(http://patchwork.ozlabs.org/patch/510674)

These patches have also been tested with as set of packetdrill scripts
located at
https://github.com/bendikro/packetdrill/tree/master/gtests/net/packetdrill/tests/linux/rdb
(The tests require patching packetdrill with a new socket option:
https://github.com/bendikro/packetdrill/commit/9916b6c53e33dd04329d29b7d8baf703b2c2ac1b)

Detailed info about the RDB mechanism can be found at
http://mlab.no/blog/2015/10/redundant-data-bundling-in-tcp, as well as
in the paper "Latency and Fairness Trade-Off for Thin Streams using
Redundant Data Bundling in TCP"[2].

[1] http://home.ifi.uio.no/paalh/students/BendikOpstad.pdf
[2] http://home.ifi.uio.no/bendiko/rdb_fairness_tradeoff.pdf

Changes:

v3 (PATCH):
* tcp-Add-Redundant-Data-Bundling-RDB:
* Changed name of sysctl variable from tcp_rdb_max_skbs to
tcp_rdb_max_packets after comment from Eric Dumazet about
not exposing internal (kernel) names like skb.
* Formatting and function docs fixes

v2 (RFC/PATCH):
* tcp-Add-DPIFL-thin-stream-detection-mechanism:
* Change calculation in tcp_stream_is_thin_dpifl based on
feedback from Eric Dumazet.

* tcp-Add-Redundant-Data-Bundling-RDB:
* Removed setting nonagle in do_tcp_setsockopt (TCP_RDB)
to reduce complexity as commented by Neal Cardwell.
* Cleaned up loss detection code in rdb_check_rtx_queue_loss

v1 (RFC/PATCH)

Bendik Rønning Opstad (2):
tcp: Add DPIFL thin stream detection mechanism
tcp: Add Redundant Data Bundling (RDB)

Documentation/networking/ip-sysctl.txt | 23 +++
include/linux/skbuff.h | 1 +
include/linux/tcp.h | 3 +-
include/net/tcp.h | 35 +++++
include/uapi/linux/tcp.h | 1 +
net/core/skbuff.c | 3 +-
net/ipv4/Makefile | 3 +-
net/ipv4/sysctl_net_ipv4.c | 35 +++++
net/ipv4/tcp.c | 16 +-
net/ipv4/tcp_input.c | 3 +
net/ipv4/tcp_output.c | 11 +-
net/ipv4/tcp_rdb.c | 273 +++++++++++++++++++++++++++++++++
12 files changed, 399 insertions(+), 8 deletions(-)
create mode 100644 net/ipv4/tcp_rdb.c

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1.9.1