[Cake] overheads or rate calculation changed?

[Andy Furniss]

Andy Furniss wrote:
> Been running a cake cobolt from april for some time using
> 
> tc qdisc add dev ppp0 handle 1:0 root cake bandwidth 19690kbit raw 
> overhead 34 diffserv4 dual-srchost nat rtt 200ms
> 
> tc -s qdisc ls dev ppp0 (ppp0 is pppoe)
> 
> qdisc cake 1: root refcnt 2 bandwidth 19690Kbit diffserv4 dual-srchost 
> nat rtt 200.0ms noatm overhead 56 via-ethernet
> 
> Which is backed off a couple of kbit and tests well (overhead 33 + udp 
> flood is over limit)
> 
> With current cobalt + current tc the same command is under rate - I 
> don't know if its rate calculation or overheads calc changed.
> 
> overhead 20 (-14) is still under but overhead 12 (-22) is over.
> 
> I was hoping one of those would be correct, but no.
> 
> Any ideas/known changes?

Bisected to -

f33c4d6a08cb21374ce52fc1438a8531bc84bcbe is the first bad commit
commit f33c4d6a08cb21374ce52fc1438a8531bc84bcbe
Author: Dave Taht <dave.taht at gmail.com>
Date:   Wed Nov 22 16:21:13 2017 -0800

     refactor cake_advance_shaper and ack_filter

     cake_advance_shaper now returns a modified len argument to
     reflect cake_overhead.
     skb_ack_filter variable replaced with ack