[LARTC] Re: further CBQ/tc documentation ds9a.nl/lartc/manpages

[bert hubert <ahu@ds9a.nl>]

On Sat, Dec 08, 2001 at 04:56:04PM -0500, jamal wrote:
> > I see that now :-) The right wording appears to be that a Prio is a
> > Work-conserving non-policing shaper.
> 
> work conserving is right. non-policing is wrong. Policing is related to
> filters. Shaping is related to schedulers. Prio is a scheduler.

Ok, so 'work-conserving' encodes the fact that it will never delay packets?

> Shaping results in non-work conserving schemes. You can attacha TBF which
> shaping inside a Prio qdisc. That would add non-workconserving-ness to it.

Ok, but pfifo_fast for example will always be work conserving.

> > New wording:
> > Do not confuse this classless simple qdisc with the classful PRIO one!
> > Although they have a lot in common, the PRIO queue can contain different
> > classes, whereas pfifo_fast has hardcoded FIFO bands.
> 
> I am not sure if i like the wording: A class is the result of a
> class-ification. Both pfifo_fast and PRIO have builtin class-ifiers.
> Essentially if you treated default prio qdisc and pfifo_fast as black
> boxes, there is _no_ difference. Dont look at the code, think larger
> picture.

Well, I aim for the user. For the user, the big picture may be identical but
the use is quite different. I don't want to get email 'I tried to add a
qdisc to pfifo_fast and it didn't work!'. 

New wording:
 Do not confuse this classless simple qdisc with the classful PRIO one!
 Although they behave similarly, pfifo_fast is classless and you cannot add
 other qdiscs to it with the tc command.

I think this covers what you mean and what I want.

> You can have two qdiscs per device, ingress and egress
> Please look at the router model i described earlier. The two hooks are
> very clearly described there.
> Ingress qdisc is work conserving only by design; whereas egress qdiscs
> could be non-work conserving.

True. The ingress qdisc isn't really dequeued.

> Again, look at the definitiions of eg/ingress. You need to have this
> diagram drawn:
> 
> http://www.davin.ottawa.on.ca/ols/img9.htm
> in your document.

It's good, will need to asciify it however.

> > other words, it delays certain packets while it doesn't delay others. How
> > would you suggest wording this?
> 
> Look at the model draft then lets talk again.

Ok. Rewording of the HOWTO will have to wait on a glossary/definition
section anyhow.

> > > the lo device); they might find that all their packets greater than 2K
> > > being dropped.
> >
> > Sure?
> 
> 100% sure. Try a little experiment then look at the code again.

I will, but I bet you 5 euros that I'm right :-) We are talking about the
TBF, aren't we?

Regards,

bert

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