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From: Dave Taht <dave@taht.net>
To: Pete Heist <peteheist@gmail.com>
Cc: Jonathan Morton <chromatix99@gmail.com>,
 Cake List <cake@lists.bufferbloat.net>
References: <71FB183D-F848-4513-A6F6-D03FD0F10769@gmail.com>
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Date: Thu, 23 Nov 2017 09:03:34 -0800
In-Reply-To: <52C2B216-220C-4C17-882C-9994867E86BB@gmail.com> (Pete Heist's
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Subject: Re: [Cake] lan keyword affects host fairness
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Pete Heist <peteheist@gmail.com> writes:

>     On Nov 23, 2017, at 10:44 AM, Jonathan Morton <chromatix99@gmail.com>=
 wrote:
>=20=20=20=20=20
>     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 r=
educed,
>     leaving little or no back-pressure for the fairness logic to work aga=
inst.

Agreed.=20

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.

>
>     For this reason, you might have better luck with the next higher RTT
>     setting.
>
> Thanks=E2=80=A6and using =E2=80=98metro=E2=80=99 (rtt 10ms) does improve =
things (two more tests at the
> end):


>
> https://docs.google.com/spreadsheets/d/1SMXWw2fLfmBRU622urfdvA_Ujsuf_KQ4P=
3uyOH1skOM/edit#gid=3D2072687073
>
> In both cases, soft rate limiting to 950mbit when using lower RTTs works =
better
> than relying on bql for the back-pressure (if I=E2=80=99m saying that rig=
ht).
>
> 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...

Yes, man page.

> Pete
>
>
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