[Cake] lan keyword affects host fairness
Marcelo Ricardo Leitner
marcelo.leitner at gmail.com
Fri Nov 24 08:15:35 EST 2017
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.
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