[Cake] Emulating Bufferbloat

[Cake] Emulating Bufferbloat

[Fabian Ruffy]

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Re: [Cake] Emulating Bufferbloat

[Toke Høiland-Jørgensen]

Fabian Ruffy <fruffy@cs.ubc.ca> writes:

> Hello,
>
> this is a somewhat esoteric question. I am trying to actually force bufferbloat
> in an emulation setup I am using. I set up a dumbbell topology and push traffic
> through it, causing congestion at the central link. I use this setup to compare
> congestion avoidance algorithms such as DCTCP to other solutions.
> This has worked nicely with the 4.18 kernel. However, after upgrading to 4.19 I
> cannot reproduce bufferbloat anymore. The traffic (even UDP packets) is
> perfectly rate limited and I never see any congestion happening. This is great,
> but in practice it prevents me from prototyping algorithms.

Ha, that's awesome! :D

> My interface configuration for bottlenecked links is:
>
>     qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat
>     12.0ms
>      Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
>      backlog 0b 0p requeues 0
>     qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500
>      Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
>      backlog 0b 0p requeues 0
>
>
> I have the suspicion that it is related to the CAKE changes in the 4.19 kernel,
> but I am not exactly sure. I am not using tc cake at all. Do you maybe know
> what could cause this behavior? Apologies if this is the wrong mailing
> list.

My guess would be changes in the TCP stack; can't point you to anything
specific off the top of my head, though...

-Toke

Re: [Cake] Emulating Bufferbloat

[Stephen Hemminger]

On Thu, 22 Nov 2018 12:28:36 -0800
Fabian Ruffy <fruffy@cs.ubc.ca> wrote:

> Hello,
> 
> this is a somewhat esoteric question. I am trying to actually force bufferbloat in an emulation setup I am using. I set up a dumbbell topology and push traffic through it, causing congestion at the central link. I use this setup to compare congestion avoidance algorithms such as DCTCP to other solutions.
> This has worked nicely with the 4.18 kernel. However, after upgrading to 4.19 I cannot reproduce bufferbloat anymore. The traffic (even UDP packets) is perfectly rate limited and I never see any congestion happening. This is great, but in practice it prevents me from prototyping algorithms.
> 
> My interface configuration for bottlenecked links is:
> 
> qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat 12.0ms
> >  Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
> >  backlog 0b 0p requeues 0
> > qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500
> >  Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
> >  backlog 0b 0p requeues 0
> 
> 
> I have the suspicion that it is related to the CAKE changes in the 4.19 kernel, but I am not exactly sure. I am not using tc cake at all. Do you maybe know what could cause this behavior? Apologies if this is the wrong mailing list.

More likely it is a combination of TCP small queues and pacing support.
To emulate a network you need to have an intermediate box, otherwise the local feedback
in TCP will defeat what you are trying to do.

Re: [Cake] Emulating Bufferbloat

[Dave Taht]

Toke Høiland-Jørgensen <toke@toke.dk> writes:

> Fabian Ruffy <fruffy@cs.ubc.ca> writes:
>
>> Hello,
>>
>> this is a somewhat esoteric question. I am trying to actually force bufferbloat
>> in an emulation setup I am using. I set up a dumbbell topology and push traffic
>> through it, causing congestion at the central link. I use this setup to compare
>> congestion avoidance algorithms such as DCTCP to other solutions.
>> This has worked nicely with the 4.18 kernel. However, after upgrading to 4.19 I
>> cannot reproduce bufferbloat anymore. The traffic (even UDP packets) is
>> perfectly rate limited and I never see any congestion happening. This is great,
>> but in practice it prevents me from prototyping algorithms.
>
> Ha, that's awesome! :D

I have not upgraded to this branch. And in general I do recomend using a
separate box. "Nuke it from orbit, it's the only way to be *sure*".

However, recently I was able to get bufferbloat by using network
namespaces for my test, and perhaps that "still works"?

In this extremely long thread there's a test setup of network namespaces
you can try:

https://github.com/systemd/systemd/issues/9725

>
>> My interface configuration for bottlenecked links is:
>>
>>     qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat
>>     12.0ms
>>      Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
>>      backlog 0b 0p requeues 0
>>     qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500
>>      Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
>>      backlog 0b 0p requeues 0
>>
>>
>> I have the suspicion that it is related to the CAKE changes in the 4.19 kernel,
>> but I am not exactly sure. I am not using tc cake at all. Do you maybe know
>> what could cause this behavior? Apologies if this is the wrong mailing
>> list.
>
> My guess would be changes in the TCP stack; can't point you to anything
> specific off the top of my head, though...
>
> -Toke
> _______________________________________________
> Cake mailing list
> Cake@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cake

Re: [Cake] Emulating Bufferbloat

[Fabian Ruffy]

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Hello,

thanks for the quick feedback! It's not even TCP, that is what is 
confusing me.

I attached two images. In this run, I am literally just pushing UDP 
packets at 10mbit per second. The first run is kernel 4.18. You can see 
that I am pushing in 10mbit on two interfaces and emit 10 mbit on the eth3.

Kernel 4.19 on the other hand looks like this:

Optimal distribution 5/5 mbit on each interface. I am quite confused.

I was hoping you guys might know, but it seems to be unrelated to cake 
or the bufferbloat changes. I might just ask the netdev guys.

Fabian

On 11/22/18 1:15 PM, Stephen Hemminger wrote:
> On Thu, 22 Nov 2018 12:28:36 -0800
> Fabian Ruffy <fruffy@cs.ubc.ca> wrote:
>
>> Hello,
>>
>> this is a somewhat esoteric question. I am trying to actually force bufferbloat in an emulation setup I am using. I set up a dumbbell topology and push traffic through it, causing congestion at the central link. I use this setup to compare congestion avoidance algorithms such as DCTCP to other solutions.
>> This has worked nicely with the 4.18 kernel. However, after upgrading to 4.19 I cannot reproduce bufferbloat anymore. The traffic (even UDP packets) is perfectly rate limited and I never see any congestion happening. This is great, but in practice it prevents me from prototyping algorithms.
>>
>> My interface configuration for bottlenecked links is:
>>
>> qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat 12.0ms
>>>   Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
>>>   backlog 0b 0p requeues 0
>>> qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500
>>>   Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
>>>   backlog 0b 0p requeues 0
>>
>> I have the suspicion that it is related to the CAKE changes in the 4.19 kernel, but I am not exactly sure. I am not using tc cake at all. Do you maybe know what could cause this behavior? Apologies if this is the wrong mailing list.
> More likely it is a combination of TCP small queues and pacing support.
> To emulate a network you need to have an intermediate box, otherwise the local feedback
> in TCP will defeat what you are trying to do.

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