[Bloat] CAKE in openwrt high CPU

[Mikael Abrahamsson]

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?

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se