[Make-wifi-fast] [Babel-users] reducing delays in wifi mcast queues

[Dave Taht]

On Tue, Sep 18, 2018 at 5:43 PM Juliusz Chroboczek <jch at irif.fr> wrote:
>
> >> Interesting.  AFAIK, ECN is only considered by AQM queues, so this implies
> >> there's a queue in the way that's dropping Babel packets.
>
> > There's fq_codel on every queue, which does FQ, and codel assumes
> > everything is at least moderately TCP friendly (and/or reasonably
> > responsive to ecn marks)
>
> Jonathan seems to agree with you.
>
> Were your tests run with more than 60 installed routes or so?

yes. I can get an exact amount of ipv4 and ipv6 routes tomorrow, it
has been well over
240 in various stages of this net's evolution, but probably below 100
as I write 'cause that
main gw is reverted to static routes right now.

> >> Or perhaps, if we know which queue that is,
> >> we could modify Babel's packet scheduling to be more AQM friendly?
>
> > How would you describe babel's packet schedulig now?
>
> The main flaw is that it sends periodic updates as a burst of back-to-back
> full-size packets.  That could trigger Codel if you had more than 60
> routes or so.
>
> > So dumping packets in there at a rate no more than 20ms each (short term
> > burst of 100ms) - relative to whatever bandwidth can be achieved vs the
> > other flows.
>
> Right.  Guilty as charged.

Well, packet pacing is now a feature of the tcp stack but not the udp
one, but it
is good to know something can be done in addition to ecn....


>
> -- Juliusz



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619