[Cerowrt-devel] BBR congestion control algorithm for TCP in net-next

Alan Jenkins alan.christopher.jenkins at gmail.com
Wed Sep 21 05:06:49 EDT 2016

On 17/09/16 19:53, Dave Taht wrote:
> BBR is pretty awesome, and it's one of the reasons why I stopped
> sweating inbound rate limiting + fq_codel as much as I used to. I have
> a blog entry pending on this but wasn't expecting the code to be
> released before the paper was... and all I had to go on til yesterday
> was Nowlan's dissertation:
> http://blog.cerowrt.org/papers/bbr_thesis.pdf

are we sure - that's a fairly different algorithm and different 
expansion of the acronym...

 > video  streaming  experiments  ran  on  a  live,  production  CDN, 
where clients included real mobile and desktop users

 > large, multinational production network

hmm, I suppose...

 > ## Acknowledgments ##
 > Van
 > ...
 > Eric
 > ...

ok, there's clearly some overlap here :-D.

> which seemed closer to good than anything I'd read before, but still
> wrong in a few respects, which has taken a few years to sort out. I
> think reading the upcoming acm queue paper is going to be fun!
> I think they have identified the right variables to probe - RTT and
> bandwidth, in sequence - for modern congestion control to work much
> better.
> Still BBR makes a few assumptions that do not hold (or so I think) -
> with wifi in the control loop, and it needs wider testing in more
> circumstances than just google facing out - like on itty bitty nas's
> and media servers - and especially seeing what happens when it
> interacts with fq_codel and cake would be good to see. I've watched
> youtube be *excellent* for 2 years now, and only had the faintest
> hints as to why.
> It was quite amusing that the original patchset didn't compile on 32
> bit platforms.
> And make no mistake - it still makes plenty of sense to apply
> fq_codel-like algorithms to routers, and the stuff we just did to wifi
> for fq_codel and airtime fairness. Had I thought BBR solved everything
> I'd have quit years ago.
> On Sat, Sep 17, 2016 at 11:34 AM, Maciej Soltysiak <maciej at soltysiak.com> wrote:
>> Hi,
>> Just saw this: https://patchwork.ozlabs.org/patch/671069/
>> Interested to see how BBR would play out with things like fq_codel or cake.
>> "loss-based congestion control is unfortunately out-dated in today's
>> networks. On
>> today's Internet, loss-based congestion control causes the infamous
>> bufferbloat problem"
>> So, instead of waiting for packet loss they probe and measure, e.g. when
>> doing slow start (here called STARTUP) they don't speed up until packet
>> loss, but slow down before reaching estimated bandwidth level.
>> Cake and fq_codel work on all packets and aim to signal packet loss early to
>> network stacks by dropping; BBR works on TCP and aims to prevent packet
>> loss.

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