[Cake] How to test Cake on TP-Link WDR3600

Alan Jenkins alan.christopher.jenkins at gmail.com
Sun Jul 26 17:05:50 EDT 2015

On 26/07/15 21:09, Alec Robertson wrote:
> I’ve just updated to the newest trunk release of OpenWRT Chaos Calmer 
> (fresh install) and the SQM QOS from OPKG interestingly does include 
> Cake as a qdisc but neither layer_cake.qos nor piece_of_cake.qos are 
> available as setup scripts.
> I’m still trying out Cake so I’ll be back soon with some feedback.

You should find the cake option there does nothing?

It'll only work if you have the "kmod-sched-cake" package providing 
/lib/modules/*/sch_cake.ko.  It's only in Dave's recent experimental builds.

fq_codel is the more supported option and serves the same functions.  If 
you can notice any difference yet, I think we'd love to hear about it.  
Currently I believe the noticeable differences are

1. if your router has TCP offloads enabled, cake undoes ("peels") it 
some to improve latency.  (Getting this past review for mainline Linux 
sounds increasingly "interesting").
2. for networks with many flows, cake works much harder to avoid "hash 
collision" (entirely?), so every flow gets a fair share. fq_codel 
defaults to 1000 hash buckets (but collision probability will increase 
well before that point, see "birthday paradox").

1) seems a real concern for some new routers.  If you are affected you 
could add a boot script using ethtool.

The idea is it's not optimal to disable offloads universally... maybe if 
you're sharing a usb drive from the router as well or something.  Having 
cake handle it works as a great default configuration.  (I just suspect 
Linux devs would ask why the feature can't be enabled on other packet 
schedulers, e.g. by using a stackable peeler qdisc).


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