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

[Dave Taht]

On Thu, Oct 27, 2016 at 10:52 AM, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> 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 !

While I chose to do so on portions of my deployment, there is the larger
problem that Apple has enabled it nearly universally on iOS and OSX
over the past year.

> ECN was a nice attempt, but suffers from implementation bugs.

Believe me, I'm not huge on it either!

>
> 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
>
>



-- 
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org