[Cake] lan keyword affects host fairness

[Sebastian Moeller]

> 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...


> 
> -Toke
> 
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