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

Neal Cardwell ncardwell at google.com
Mon Sep 26 15:30:13 EDT 2016

On Mon, Sep 26, 2016 at 2:47 PM, Aaron Wood <woody77 at gmail.com> wrote:
> Dumb question on this:  The tcp_bbr_info struct for a socket can be
> inspected at runtime through the ss utility or through a get socket opts
> call, right?

Yes, you can use either approach:

(1) from code you can use TCP_CC_INFO socket option; there is sample
code in the original kernel patch for TCP_CC_INFO:

(2) from ss: if you download and build the net-next branch of the
iproute2 package:
  then you will get support to print out the main parameters for a BBR
connection, eg:

  The patch with BBR support for ss is here:

  As the commit notes, the BBR output looks like:

Hope that helps,

> -Aaron
> 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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>> Cerowrt-devel at lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
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