Re: [aqm] [Bloat] TCP BBR paper is now generally available

Neal Cardwell <ncardwell@google.com> Fri, 02 December 2016 22:22 UTC

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From: Neal Cardwell <ncardwell@google.com>
Date: Fri, 2 Dec 2016 17:22:23 -0500
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To: Jonathan Morton <chromatix99@gmail.com>
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Cc: Aaron Wood <woody77@gmail.com>, "aqm@ietf.org" <aqm@ietf.org>, bloat <bloat@lists.bufferbloat.net>
Subject: Re: [aqm] [Bloat] TCP BBR paper is now generally available
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On Fri, Dec 2, 2016 at 3:32 PM, Jonathan Morton <chromatix99@gmail.com>
wrote:

>
> > On 2 Dec, 2016, at 21:15, Aaron Wood <woody77@gmail.com> wrote:
> >
> > So, how is this likely to be playing with our qos_scripts and with cake?
>
> Cake’s deficit-mode shaper behaves fairly closely like an ideal
> constant-throughput link, which is what BBR is supposedly designed for.


Great. Yes, that's right: BBR's favorite case is a constant-throughput link
or shaper, since that's the easiest to model.


>   I haven’t read that far in the paper yet, but it shouldn’t trigger any
> “bucket detection” algorithms, because it doesn’t have a “bucket”.  It is
> capable of bursting, but only to the minimum extent required to reconcile
> required throughput with timer resolution and scheduling latency; I’ve
> tested it with millisecond timers.
>

That's also good to hear. If it doesn't have a "bucket" or allow
unsustainable bursts, then it should work well with BBR, and shouldn't
trigger the long-term/policer model.

Of course, if we find important use cases that don't work with BBR, we will
see what we can do to make BBR work well with them.

cheers,
neal