[Cake] [lede-project/source] Add support for cake qdisc (#72)

Benjamin Cronce bcronce at gmail.com
Wed Jun 1 08:25:54 EDT 2016

On Wed, Jun 1, 2016 at 6:57 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:

> Hi Kevin
> On June 1, 2016 1:47:42 PM GMT+02:00, Kevin Darbyshire-Bryant <
> kevin at darbyshire-bryant.me.uk> wrote:
> >
> >
> >On 01/06/16 12:41, moeller0 wrote:
> >> Hi Toke,
> >>> I'm guessing this was probably discussed before and I've simply
> >>> forgotten; but why does this (rewriting dscp bits) need to be part
> >of
> >>> the qdisc when you can do it with iptables?
> >>
> >>      Well, cake looks at the DSCP bits already, if it can do the
> >re-mapping we potentially would not need to touch iptables at all,
> >which cakes goal being simplicity seemed on-focus. But since this
> >feature turned out to be contentious, I vote for throwing it out and
> >just rely on iptables… I believe Jonathan argued that the re-mapping
> >really is an orthogonal issue that does not conceptually belong into a
> >qdisc, a valid points as by now everyone agrees…
> >>
> >> Best Regards
> >>          Sebastian
> >
> >One silly question from ignorant fool:  Can you do the iptables DSCP
> >remapping in such a way that the qdisc still sees/prioritize based on
> >them but clear/remap on output?
> At least on ingress that is all we can do right now, as the iptables gets
> only run after the intermediate functional block device. So we can
> explicitly not do what we like, that is to use iptables to re-mapp DSCP
> marks to our internal liking and then have these Interpreten to select the
> correct priority tin... Re-map all to 0 is just a special case of that...
> Best Regards
>        Sebastian
> >
> >Kevin
I'm just going to ask two questions just to reflect on

1) Ideally, regardless of platform, should an AQM or scheduler have the
responsibility of changing anything other than ECN?
2) Should you be deciding the responsibility of CAKE based on the
implementation of the platform (IP Tables, not IPTables, etc) or
implementing the ideal solution?

Ideals can be bad if overly zealous, but it's a slippery slope to the
anti-ideal every time you give up an ideal for practical reasons. I always
ask myself, what is the perfect solution, can it be done, and what are the
trade-offs if it cannot be. Single point of responsibility is one of those
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