[Cake] A few puzzling Cake results

Toke Høiland-Jørgensen toke at toke.dk
Tue Apr 17 10:17:50 EDT 2018

Jonathan Morton <chromatix99 at gmail.com> writes:

>> On 17 Apr, 2018, at 12:42 pm, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> - The TCP RTT of the 32 flows is *way* higher for Cake. FQ-CoDel
>>  controls TCP flow latency to around 65 ms, while for Cake it is all
>>  the way up around the 180ms mark. Is the Codel version in Cake too
>>  lenient, or what is going on here?
> A recent change was to increase the target dynamically so that at
> least 4 MTUs per flow could fit in each queue without AQM activity.
> That should improve throughput in high-contention scenarios, but it
> does come at the expense of intra-flow latency when it's relevant.

Ah, right, that might explain it. In the 128 flow case each flow has
less than 100 Kbps available to it, so four MTUs are going to take a
while to dequeue...

> To see whether Diffserv actually prioritises correctly, you'll need to
> increase the number of bulk flows beyond the point where the VoIP flow
> no longer receives the bandwidth it needs purely from its fair share
> of the link.

Yup, which is what I have been unable to do for the VoIP flow case. I
guess I'll have to try with a flow that has a bit higher bandwidth...


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