Re: [Bloat] Initial tests with BBR in kernel 4.9

[Hans-Kristian Bakke <hkbakke@gmail.com>]

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I did some more testing with fq as a replacement of pfifo_fast and it now
behaves just as good. It must have been some strange artifact. My questions
are still standing however.

Regards,
Hans-Kristian

On 25 January 2017 at 21:54, Hans-Kristian Bakke <hkbakke@gmail.com> wrote:

> Hi
>
> Kernel 4.9 finally landed in Debian testing so I could finally test BBR in
> a real life environment that I have struggled with getting any kind of
> performance out of.
>
> The challenge at hand is UDP based OpenVPN through europe at around 35 ms
> rtt to my VPN-provider with plenty of available bandwith available in both
> ends and everything completely unknown in between. After tuning the
> UDP-buffers up to make room for my 500 mbit/s symmetrical bandwith at 35 ms
> the download part seemed to work nicely at an unreliable 150 to 300 mbit/s,
> while the upload was stuck at 30 to 60 mbit/s.
>
> Just by activating BBR the bandwith instantly shot up to around 150 mbit/s
> using a fat tcp test to a public iperf3 server located near my VPN exit
> point in the Netherlands. Replace BBR with qubic again and the performance
> is once again all over the place ranging from very bad to bad, but never
> better than 1/3 of BBRs "steady state". In other words "instant WIN!"
>
> However, seeing the requirement of fq and pacing for BBR and noticing that
> I am running pfifo_fast within a VM with virtio NIC on a Proxmox VE host
> with fq_codel on all physical interfaces, I was surprised to see that it
> worked so well.
> I then replaced pfifo_fast with fq and the performance went right down to
> only 1-4 mbit/s from around 150 mbit/s. Removing the fq again regained the
> performance at once.
>
> I have got some questions to you guys that know a lot more than me about
> these things:
> 1. Do fq (and fq_codel) even work reliably in a VM? What is the best
> choice for default qdisc to use in a VM in general?
> 2. Why do BBR immediately "fix" all my issues with upload through that
> "unreliable" big BDP link with pfifo_fast when fq pacing is a requirement?
> 3. Could fq_codel on the physical host be the reason that it still works?
> 4. Do BBR _only_ work with fq pacing or could fq_codel be used as a
> replacement?
> 5. Is BBR perhaps modified to do the right thing without having to change
> the qdisc in the current kernel 4.9?
>
> Sorry for long post, but this is an interesting topic!
>
> Regards,
> Hans-Kristian Bakke
>

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