Re: [Bloat] "BBR" TCP patches submitted to linux kernel

[Ingemar Johansson S <ingemar.s.johansson@ericsson.com>]

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 <eric.dumazet@gmail.com>
> To: Dave Taht <dave.taht@gmail.com>
> Cc: "Steinar H. Gunderson" <sgunderson@bigfoot.com>, bloat
> 	<bloat@lists.bufferbloat.net>
> 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
> 
> 
> 
> 
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