> On 24 Oct 2015, at 08:11, Yuchung Cheng <ych...@google.com> wrote: > > On Fri, Oct 23, 2015 at 1:50 PM, Bendik Rønning Opstad > <bro.de...@gmail.com> wrote: >> >> This is a request for comments. >> >> 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 a recently submitted patch for >> tcp_skb_cb (tcp: refactor struct tcp_skb_cb: >> http://patchwork.ozlabs.org/patch/510674) >> >> These patches have 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 > > What's the difference between RDB and TCP repacketization > (http://flylib.com/books/en/3.223.1.226/1/) ? > > Reading the blog page, I am concerned the amount of > change (esp on fast path) just to bundle new writes during timeout & > retransmit, for a specific type of application? why not just send X > packets with total bytes < MSS on timeout..
Repacketization is only on retransmissions; RDB bundles previously sent segments with the next “normal” transmission instead. This makes the flow recover the lost segment before a retransmission is triggered by an RTO or fast retransmit. >> "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 >> >> >> 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 | 9 +- >> include/net/tcp.h | 34 ++++ >> 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 | 19 ++- >> net/ipv4/tcp_input.c | 3 + >> net/ipv4/tcp_output.c | 11 +- >> net/ipv4/tcp_rdb.c | 281 >> +++++++++++++++++++++++++++++++++ >> 12 files changed, 415 insertions(+), 8 deletions(-) >> create mode 100644 net/ipv4/tcp_rdb.c >> >> -- >> 1.9.1 N�����r��y����b�X��ǧv�^�){.n�+����{�j����^n�r���z���h�����&�� �G���h�(�階�ݢj"���m������z�ޖ���f���h���~�m�
