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Re: ATM performance vs. IP QoS

Rui Prior wrote:
> First of all, I worked around the problem by enforcing an artificial limit on 
> the queue size for CBR VCs. Maybe it would be nice to have some means of 
> configuring this limit at runtime, preferably on a per-vc basis. Any 
> suggestion?

Well, that's what the sndbuf option is supposed to do in the case of
atmarp. Applications using "native ATM" just set the socket send
buffer directly.

> What do you mean by "still accounted for by the ATM stack"?

I.e. that you haven't called vcc->pop yet.

> The driver doesn't copy TX buffers, so SKBs are not freed by the driver until 
> they're effectively transmitted.

So it seems that sndbuf will do exactly what you need.

> I was thinking of a temporary workaround for my QoS tests (now I've modified 
> the driver I don't need it anymore), so I was thinking of using a TBF as 
> outer qdisc. Of course I hadn't thought straight: as TBF is classless there's 
> no way to make it work as outer qdisc...

Yeah, wouldn't it be nice ;-) Actually, CBQ should be able to do
about the same thing. One of these days, I might even try to figure
out how :-)

- Werner

 / Werner Almesberger, ICA, EPFL, CH           Werner.Almesberger@epfl.ch /