Hi Eric + others Cubic : I would believe that the main reason why Cubic give such bad results lies in the HyStart algorithm, I have sofar not seen any major issues with the Cubic congestion avoidance algorithm, provided of course that proper AQM is deployed.
RFC3540 : This actually in the process of becoming historic (see https://datatracker.ietf.org/doc/draft-black-tsvwg-ecn-experimentation/ ), also you will notice that I am on favor of this draft as I am among the folks who wish to free up ECT(1) for L4S use. /Ingemar > Message: 5 > Date: Thu, 27 Oct 2016 10:52:08 -0700 > From: Eric Dumazet <[email protected]> > To: Dave Taht <[email protected]> > Cc: "Steinar H. Gunderson" <[email protected]>, bloat > <[email protected]> > Subject: Re: [Bloat] "BBR" TCP patches submitted to linux kernel > Message-ID: > <1477590728.7065.231.camel@edumazet- > glaptop3.roam.corp.google.com> > Content-Type: text/plain; charset="UTF-8" > > On Thu, 2016-10-27 at 10:33 -0700, Dave Taht wrote: > > > At the moment my biggest beef with BBR is that it ignores ECN entirely > > (and yet negotiates it). > > Note that switching cubic to any other CC like BBR is allowed at any > time, way after ECN was negotiated. > > So BBR can not solve the issue you mention in a reliable way. > > There must be a reason sysctl_tcp_ecn default value is 2 on linux [1], > don't you think ??? > > _You_ chose to change this sysctl, do not blame BBR for being silly ! > > ECN was a nice attempt, but suffers from implementation bugs. > > For a start, linux does not implement RFC 3540. > > If someone cares enough of ECN, then it should cook linux patches to > implement RFC 3540. Hint hint hint. > > Then you need to make sure all the nodes between your peers are not > messing with ECN. > > BBR simply works, because it is a sender side thing. > You do not have to fix everything in the Internet. > > [1] > Documentation/networking/ip-sysctl.txt > tcp_ecn - INTEGER > Control use of Explicit Congestion Notification (ECN) by TCP. > ECN is used only when both ends of the TCP connection indicate > support for it. This feature is useful in avoiding losses due > to congestion by allowing supporting routers to signal > congestion before having to drop packets. > Possible values are: > 0 Disable ECN. Neither initiate nor accept ECN. > 1 Enable ECN when requested by incoming connections and > also request ECN on outgoing connection attempts. > 2 Enable ECN when requested by incoming connections > but do not request ECN on outgoing connections. > Default: 2 > > > > *********************** _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
