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

[Dave Taht]

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

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.
>
>
> Best regards,
> Maciej
>
>
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-- 
Dave Täht
Let's go make home routers and wifi faster! With better software!
http://blog.cerowrt.org