[Cake] lan keyword affects host fairness

[Pete Heist]

> 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.
> 
> For this reason, you might have better luck with the next higher RTT setting.
> 
Thanks…and using ‘metro’ (rtt 10ms) does improve things (two more tests at the end):

https://docs.google.com/spreadsheets/d/1SMXWw2fLfmBRU622urfdvA_Ujsuf_KQ4P3uyOH1skOM/edit#gid=2072687073

In both cases, soft rate limiting to 950mbit when using lower RTTs works better than relying on bql for the back-pressure (if I’m saying that right).

So it just might be a thing (for the man page?) to avoid confusion. Or a warning emitted in some cases? Maybe there are other opinions on that...

Pete

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