[Bloat] CAKE in openwrt high CPU

[Sebastian Moeller]

HI Jonathan,

> On Sep 1, 2020, at 17:41, Jonathan Foulkes <jf at jonathanfoulkes.com> wrote:
> 
> Toke, that link returns a 404 for me.
> 
> For others, I’ve found that testing cake throughput with isolation options enabled is tricky if there are many competing connections. 

	Are you talking about the fact that with competing connections, you only see the current isolation quantum's equivalent f the actual rate? In that case maybe parse the "tc -s qdisc" output to get an idea how much data/packets cake managed to push through in total in each direction instead of relaying on the measured goodput? I am probably barking up the wrong tree here...

> Like I keep having to tell my customers, fairness algorithms mean no one device will ever gain 100% of the bandwidth so long as there are other open & active connections from other devices.

	That sounds like solid advice ;) Especially in the light of the exceedingly useful "ingress" keyword, which under-load-will drop depending on a flow's "unresponsiveness" such that more responsive flows end up getting a somewhat bigger share of the post-cake throughput...

> 
> That said, I’d love to find options to increase throughput for single-tin configs.

	With or without isolation options?

Best Regards
	Sebastian

> 
> Cheers,
> 
> Jonathan
> 
>> On Aug 31, 2020, at 7:35 AM, Toke Høiland-Jørgensen via Bloat <bloat at lists.bufferbloat.net> wrote:
>> 
>> 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
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