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Message-ID: <61F74109-9FDC-485A-978B-714B7AA27445@ifi.uio.no> Date: Sat, 24 Oct 2015 08:00:41 +0000 From: Jonas Markussen <jonassm@....uio.no> To: Yuchung Cheng <ycheng@...gle.com> CC: Bendik Rønning Opstad <bro.devel@...il.com>, "David S. Miller" <davem@...emloft.net>, Alexey Kuznetsov <kuznet@....inr.ac.ru>, James Morris <jmorris@...ei.org>, Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>, Patrick McHardy <kaber@...sh.net>, Jonathan Corbet <corbet@....net>, Eric Dumazet <edumazet@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, Tom Herbert <tom@...bertland.com>, Paolo Abeni <pabeni@...hat.com>, Erik Kline <ek@...gle.com>, Hannes Frederic Sowa <hannes@...essinduktion.org>, Al Viro <viro@...iv.linux.org.uk>, Jiri Pirko <jiri@...nulli.us>, Alexander Duyck <alexander.h.duyck@...hat.com>, "Florian Westphal" <fw@...len.de>, Daniel Lee <Longinus00@...il.com>, "Marcelo Ricardo Leitner" <mleitner@...hat.com>, Daniel Borkmann <daniel@...earbox.net>, "Willem de Bruijn" <willemb@...gle.com>, Linus Lüssing <linus.luessing@...3.blue>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org>, "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>, Andreas Petlund <apetlund@...ula.no>, Carsten Griwodz <griff@...ula.no>, Pål Halvorsen <paalh@...ula.no>, Kristian Evensen <kristian.evensen@...il.com>, Kenneth Klette Jonassen <kennetkl@....uio.no>, Bendik Rønning Opstad <bro.devel+kernel@...il.com> Subject: Re: [PATCH RFC net-next 0/2] tcp: Redundant Data Bundling (RDB) > On 24 Oct 2015, at 08:11, Yuchung Cheng <ycheng@...gle.com> wrote: > > On Fri, Oct 23, 2015 at 1:50 PM, Bendik Rønning Opstad > <bro.devel@...il.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
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