[Bloat] CAKE in openwrt high CPU

[Toke Høiland-Jørgensen]

Mikael Abrahamsson via Bloat <bloat at lists.bufferbloat.net> writes:

> Hi,
>
> I migrated to an APU2 (https://www.pcengines.ch/apu2.htm) as residential 
> router, from my previous WRT1200AC (marvell armada 385).
>
> I was running OpenWrt 18.06 on that one, now I am running latest 19.07.3 
> on the APU2.
>
> Before I had 500/100 and I had to use FQ_CODEL because CAKE took too much 
> CPU to be able to do 500/100 on the WRT1200AC. Now I upgraded to 1000/1000 
> and tried it again, and even the APU2 can only do CAKE up to ~300 
> megabit/s. With FQ_CODEL I get full speed (configure 900/900 in SQM in 
> OpenWrt).
>
> Looking in top, I see sirq% sitting at 50% pegged. This is typical what I 
> see when CPU based forwarding is maxed out. From my recollection of 
> running CAKE on earlier versions of openwrt (17.x) I don't remember CAKE 
> using more CPU than FQ_CODEL.
>
> Anyone know what's up? I'm fine running FQ_CODEL, it solves any 
> bufferbloat but... I thought CAKE supposedly should use less CPU, not 
> more?

Hmm, you say CAKE and FQ-Codel - so you're not enabling the shaper (that
would be FQ-CoDel+HTB)? An exact config might be useful (or just the
output of tc -s qdisc).

If you are indeed not shaping, maybe you're hitting the issue fixed by this commit?

https://github.com/dtaht/sch_cake/commit/3152477235c934022049fcddc063c45d37ec10e6n

-Toke