[Cake] Fighting bloat in the face of uncertinty

Justin Kilpatrick justin at althea.net
Sat Sep 7 18:42:55 EDT 2019

I'm using Cake on embedded OpenWRT devices. You probably saw this video on the list a month or two ago. 


Anyways up until now I've left cake totally untuned and had pretty great results. But we've finally encountered a scenario where untuned Cake allowed for unacceptable bufferbloat on a link.

Hand configuration in accordance with the best practices provided in the RFC works out perfectly, but I need a set of settings I can ship with any device with the expectation that it will be used and abused in many non-standard situations. Producing non-optimal outcomes is fine, producing dramatically degraded outcomes is unacceptable. 

Which leads to a few questions

1) What happens if the target is dramatically too low? 

Most of our links can expect latency between 1-10ms, but they may occasionally go much longer than that. What are the consequences of having a 100ms link configured with a target of 10ms?

2) If interval is dramatically unpredictable is it best to err on the side of under or over estimating?

 The user may select an VPN/exit server of their own choosing, the path to it over the network may change or the exit may be much further away. Both 10ms and 80ms would be sane choices of target depending on factors that may change on the fly. 

Thanks for the feedback! 

  Justin Kilpatrick
  justin at althea.net

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