[Cake] cake/tc - removal of atm/ptm/ethernet specific overhead keywords

[Jonathan Morton]

> On 2 Jun, 2016, at 12:37, Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> wrote:
> 
> I'd be sort of interested to know if anyone is actually using those keywords: ipoa-vcmux, ipoa-llcsnap, bridged-vcmux, bridged-llcsnap, ppoa-vcmux, pppoa-llc, pppoe-vcmux, pppoe-llcsnap, pppoe-ptm, bridged-ptm, via-ethernet, ether-phy, ether-all, ether-fcs, ether-vlan.
> 
> How many actually knew they even existed?

Since they are poorly documented, probably not many.  But I’d rather improve the documentation than delete them.

In principle, the existence and naming of these keywords is a potential clue to the uninitiated user of the overhead feature’s purpose.  The concept of protocol overhead affecting shader function is not an obvious one outside of networking specialists; making users look up a number in a cryptic table will simply result in nobody doing it at all.

Having shortcut keywords for this purpose in tc also helps to avoid the trap of other UI layers doing their own (incomplete or inaccurate) research on the correct compensation to apply.  Currently LuCI is extremely clumsy at handling SQM configuration, and the general quality of vendor firmware doesn’t give me confidence.

I’ve just pushed an update which makes all the keywords incremental, rather than some of them being absolute.  Existing correct examples of how to use these keywords remain correct.

It would be nice if LuCI could infer information about the likely overheads from the rest of the configuration, and apply (or suggest & default) the correct keywords in sqm-scripts.  That would make the feature much more widely used.

 - Jonathan Morton