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: v6 (PATCH): * tcp-Add-Redundant-Data-Bundling-RDB: * Renamed rdb_ack_event() to tcp_rdb_ack_event() (Thanks DaveM) * Minor doc changes * tcp-Add-DPIFL-thin-stream-detection-mechanism: * Minor doc changes v5 (PATCH): * tcp-Add-Redundant-Data-Bundling-RDB: * Removed two unnecessary EXPORT_SYMOBOLs (Thanks Eric) * Renamed skb_append_data() to tcp_skb_append_data() (Thanks Eric) * Fixed bugs in additions to ipv4_table (sysctl_net_ipv4.c) * Merged the two if tests for max payload of RDB packet in rdb_can_bundle_test() * Renamed rdb_check_rtx_queue_loss() to rdb_detect_loss() and restructured to reduce indentation. * Improved docs * Revised commit message to be more detailed. * tcp-Add-DPIFL-thin-stream-detection-mechanism: * Fixed bug in additions to ipv4_table (sysctl_net_ipv4.c) v4 (PATCH): * tcp-Add-Redundant-Data-Bundling-RDB: * Moved skb_append_data() to tcp_output.c and call this function from tcp_collapse_retrans() as well. * Merged functionality of create_rdb_skb() into tcp_transmit_rdb_skb() * Removed one parameter from rdb_can_bundle_test() 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 | 36 ++++++ include/uapi/linux/tcp.h | 1 + net/core/skbuff.c | 2 +- net/ipv4/Makefile | 3 +- net/ipv4/sysctl_net_ipv4.c | 34 +++++ net/ipv4/tcp.c | 16 ++- net/ipv4/tcp_input.c | 3 + net/ipv4/tcp_output.c | 48 ++++--- net/ipv4/tcp_rdb.c | 228 +++++++++++++++++++++++++++++++++ 12 files changed, 375 insertions(+), 23 deletions(-) create mode 100644 net/ipv4/tcp_rdb.c -- 1.9.1
