[Cake] Cake throughput levels off during longs tests

[Toke Høiland-Jørgensen]

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

> So I ran a couple of tests of Cake on the Archer-c7 on newest openwrt
> trunk with sqm-scripts set to 30/30 Mbps. The attached graphs are the
> result of equivalent fq_codel and cake settings.
>
> As you can see, the cake throughput levels off over long test durations.
> Anyone has any idea why?

Right, so did some more experiments, and this is definitely related to
CPU usage. I did a new build of openwrt with an updated toolchain, and
now the archer runs fine with Cake at 30 Mbps symmetrical. However, it
starts to struggle at 50 Mbps; but only after around three minutes of
continuous load.

See the comparison graphs here:
https://kau.toke.dk/experiments/cake/archer/cake-30-50.png

That directory also contains the full Flent data files and packet dumps.

So the question is now, of course, is there anything that can be done
about this, or should we simply accept that the box is out of oomph? The
way it behaves does strike me as weird...

-Toke