[Cake] lan keyword affects host fairness

[Marcelo Ricardo Leitner]

On Fri, Nov 24, 2017 at 01:06:12PM +0100, Sebastian Moeller wrote:
> 
> > On Nov 24, 2017, at 12:21, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> > 
> > Dave Taht <dave at taht.net> writes:
> > 
> >> Pete Heist <peteheist at gmail.com> writes:
> >> 
> >>>    On Nov 23, 2017, at 10:44 AM, Jonathan Morton <chromatix99 at gmail.com> wrote:
> >>> 
> >>>    This is most likely an interaction of the AQM with Linux' scheduling
> >>>    latency.
> >>> 
> >>>    At the 'lan' setting, the time comstants are similar in magnitude to the
> >>>    delays induced by Linux itself, so congestion might be signalled
> >>>    prematurely. The flows will then become sparse and total throughput reduced,
> >>>    leaving little or no back-pressure for the fairness logic to work against.
> >> 
> >> Agreed. 
> >> 
> >> man page add:
> >> 
> >> At the 'lan' setting(1ms), the time constants are similar in magnitude
> >> to the jitter in the Linux kernel itself, so congestion might be
> >> signalled prematurely. The flows will then become sparse and total
> >> throughput reduced, leaving little or no back-pressure for the fairness
> >> logic to work against. Use the "metro" setting for local lans unless you
> >> have a custom kernel.
> > 
> > Erm, doesn't this make the 'lan' keyword pretty much useless? So why not
> > just remove it? Or redefine it to something that actually works? 3ms?
> 
> The same applies for datacentre (0.1 ms), no? But I agree, let's not expose these as explicit keywords, one can always use "rtt [100us|1ms]" I assume...

Which should also contain such disclaimer with it.
"Values smaller than 10ms requires special handling.", for example.

  Marcelo