[Cake] a bunch of sch_cake vs everything tests at 100mbit on net-next

[Toke Høiland-Jørgensen]

Dave Taht <dave.taht at gmail.com> writes:

> I wanted to look at a few things - cpu usage, 4 different tcps,
> different server schedulers, ecn vs non-ecn, sqm fq_codel simplest.qos
> vs cake, etc, etc. I just did tcp_ndown tests of 128 flows to see what
> happened for starters. I also tried to capture tcp_cwnd, etc, stats,
> but that seems not to be plotting in flent....
>
> My first objective, of course, was to make sure upstream cake didn't
> crash. It didn't. No real surprises, cake ecn causes some more
> collateral inter-packet latency damage, cake (aside from general cpu
> over-usage) is a mild win across the board... including, surprisingly,
> tail drop queue depth. (see below)
>
> metric ton of flent files: http://www.taht.net/~d/cake_128flows.tgz
> (script therein)
> topology: server -> apu2 -> switch -> client (no switch between the
> apu2 and server)
>
> A couple notes:
>
> 1) ecn_vs_bbr_ineffective.png:
>
> vs bbr in ecn mode, (thus rendering codel or cake ineffective and
> reverting to tail drop) "sqm simplest.qos" at this speed (100mbit)
> uses a too large packet limit vs what cake uses. I will argue in favor
> of using the new "memlimit" parameter to fq_codel in the sqm scripts
> to better limit the buffer size.

Openwrt carries a patch to default the memlimit to 4 MB rather than 32...

-Toke