Re: [Bloat] geoff huston's take on BBR

[Dave Taht <dave.taht@gmail.com>]

On Tue, Jun 12, 2018 at 4:40 AM, Dave Taht <dave.taht@gmail.com> wrote:
> On Tue, Jun 12, 2018 at 12:36 AM, Bless, Roland (TM)
> <roland.bless@kit.edu> wrote:
>> Hi,
>>
>> Am 12.06.2018 um 07:09 schrieb Matthias Tafelmeier:
>>> On 06/12/2018 02:42 AM, Toke Høiland-Jørgensen wrote:
>>>>> https://ripe76.ripe.net/presentations/10-2018-05-15-bbr.pdf
>>>> "More research needed". Naturally ;)
>>>>
>>>> (But yeah, good points overall)
>>>
>>> Interesting. Potentially, all affectuated. After having applied the BBR
>>> 2.0, we might are back to Cubic? :D
>>
>> I don't understand what you're saying. I think Geoff tested BBR v1.0.
>> Explanations for the experienced behavior can be found in our paper
>> http://doc.tm.kit.edu/2017-kit-icnp-bbr-authors-copy.pdf, esp. section
>> 3. Geoff's findings in the wild nicely confirm our results that were
>> performed in more controlled lab settings. Important is though, that
>> you always test with multiple concurrent BBR flows...
>
> we always do that, 'round here, with flent. Glad more folk are doing it. :)

OK, I read your paper. (It's 4am, can't sleep)

My principal observation remains the same: e2e fairness is nearly
hopeless on short
timescales.

FQ solves most of it, and even if if the rfc8290 aqm component is
targetted at cubics
response curve (and bbr treats it as noise), the resulting delay curve
in the fq'd
environment seemed to get BBR on the right track on it's first probe
(except when many flows were
started concurrently), but I didn't delve deep into it at the time.

I would love it if you could redo your tests with cake managing the
bottleneck link.
(we've got a bug in the thing right now at 40+gige, but...)

https://arxiv.org/abs/1804.07617

>>> Moreover, if it tends to be unstable on larger scale - what is Google
>>> doing then? Thought they've got a more or less homogeneous BBR driven
>>> TCP flow ecosystem - at least internally!? Was all propaganda? When
>>> speculating, might working for them since of centrally handled flow
>>> steering approaches - "imposing inter-flow fairness".
>>
>> There are certain situations where BBR might work well:
>> 1) you only have a single flow at the bottleneck, might be the case in
>> their B4 scenario
>> 2) The senders a application limited (e.g., YouTube)
>
> I think the application limited scenario is the primary one. once
> typical links are fully capable of video streaming
> 4k video a lot of the demand for better congestion control will drop.
>
>> 3) The bottleneck buffer is much larger than a BDP
>>    (then BDP will limit the queue size between 1 and 1.5 BDP)
>
> Sadly we still see 2sec queues on cmtses, in particular.
>
>> However, BBR has no explicit fairness mechanism, so sometimes
>> one will see quite unfair shares for longer periods,
>> even if there are only BBR flows present at then bottleneck.
>
> except with fq at the bottleneck.
>
>>
>> Regards
>>  Roland
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>
>
>
> --
>
> Dave Täht
> CEO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-669-226-2619



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619