[c-nsp] ingress vs egress queues

[Phil Mayers]

On 03/04/2011 05:10 AM, Mack McBride wrote:

> Ingress queues can be useful/essential on some platforms:
> 6500, 7600, ASR 9K, CSR, ASR 1K (the last two are technically routers,
> ASR 9K shares a LOT with the first two but is classified as a router)

I can't speak for the ASR or CSR platforms, but the OP did say "Catalyst".

In what situations are ingress queues useful on a 6500/7600?

I'm going to go out on a limb and say they're almost always useless on 
67xx linecards, because the fabric will very, very rarely apply 
backpressure and cause ingress queueing to kick in.

Presumably they might be useful on a 6716 in oversubscribed mode. OTOH 
since the 6708 has local switching, it seems they'd be useless on that 
linecard - the embedded DFC and on-linecard mini-fabric (can't remember 
the right term) will never apply backpressure.

You hint at this lower down; but maybe they're more useful on older 
linecards like 6148 or 65xx (cef256) linecards?

Genuinely curious to hear real-world use-cases for the ingress queueing 
on 6500/7600.