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

[Neal Cardwell]

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:
   https://patchwork.ozlabs.org/patch/465806/

(2) from ss: if you download and build the net-next branch of the
iproute2 package:
    http://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/log/?h=net-next
  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:
    http://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/commit/?h=net-next&id=2f0f9aef94129643133363b4503468cdccc481cc

  As the commit notes, the BBR output looks like:
    bbr:(bw:1.2Mbps,mrtt:18.965,pacing_gain:2.88672,cwnd_gain:2.88672)

Hope that helps,
neal

>
> -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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