Re: [Bloat] "BBR" TCP patches submitted to linux kernel

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

On Thu, Oct 27, 2016 at 10:57 AM, Yuchung Cheng <ycheng@google.com> wrote:
> On Thu, Oct 27, 2016 at 10:33 AM, Dave Taht <dave.taht@gmail.com> wrote:
>> On Thu, Oct 27, 2016 at 10:04 AM, Steinar H. Gunderson
>> <sgunderson@bigfoot.com> wrote:
>>> On Fri, Oct 21, 2016 at 10:47:26AM +0200, Steinar H. Gunderson wrote:
>>>> As a random data point, I tried a single flow from my main server in .no
>>>> to my backup server in .nl and compared CUBIC (with sch_fq) to BBR (naturally
>>>> also in sch_fq) on the sender side. The results were quite consistent across
>>>> runs:
>>>
>>> Another datapoint: A friend of mine had a different, worse path (of about 40 ms)
>>> and tested with iperf.
>>>
>>> CUBIC delivered 20.1 Mbit/sec (highly varying). BBR delivered 485 Mbit/sec.
>>
>> I mostly live in a world (wifi) where loss is uncommon, unless forced
>> on it with a AQM.
>>
>> At the moment my biggest beef with BBR is that it ignores ECN entirely
>> (and yet negotiates it). BBR is then so efficient at using up all the
>> pipe that a single queued aqm "marks madly" and everything else
>> eventually starves. Watch "ping" fade out here...
>>
>> http://blog.cerowrt.org/flent/bbr-comprehensive/bbr_ecn_eventually_starving_ping.png
>
> Thanks Dave for this issue. We design BBR with CoDel in mind b/c Van
> co-designs both :)

It works pretty darn good with codel without ecn. I'm pretty darn happy with it.

fq_codel is even more lovely, especially when competing with cubic.

There are issues with single queued aqms with BBR vs cubic

http://blog.cerowrt.org/flent/bbr-ecncaps/bandwidth-share-creaming-cubic-flowblind-aqm.svg

> We have tested BBR with CoDel before and it works.

Well, against cubic on the same link in single queue mode, even
without ecn, life looks like this:

http://blog.cerowrt.org/flent/bbr-ecncaps/bandwidth-share-creaming-cubic-flowblind-aqm.svg

but fq_codel is fine, so long as there is no ecn vs nonecn collission

http://blog.cerowrt.org/flent/bbr-ecncaps/bandwidth-share-ecn-fq.png

> Could you share your tcpdump traces with us (maybe
> you already did but no sure) or suggest how to reproduce this.
>
> This is 2 bbr flow or bbr + ecn-cubic? (I am guessing based on caption
> in your graph)

That's two BBRs with ecn enabled, going through cake in the single
queue aqm mode "flowblind". I have similar plots with pie and codel
with ecn enabled somewhere.

The emulation is 48ms RTT, 20Mbit down, 5Mbit up.

Regrettably I'm on a couple deadlines (a talk tomorrow, and next
thursday), and can't look harder, I do have caps comparing ecn vs
noecn here

http://blog.cerowrt.org/flent/bbr-ecncaps/



>
>>
>> somewhat conversely in fq_codel, this means that it ignores codel's
>> marking attempts entirely and BBR retains it's own dynamics, (while
>> the non-BBR flows are fine) which is kind of neat to watch.
>>
>>> /* Steinar */
>>> --
>>> Homepage: https://www.sesse.net/
>>> _______________________________________________
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>>
>>
>>
>> --
>> Dave Täht
>> Let's go make home routers and wifi faster! With better software!
>> http://blog.cerowrt.org
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-- 
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org