[c-nsp] 3845 maxing out at 400 Mbps

[Frank Bulk]

We have two 3845's as border routers, each with three GigE interfaces (one
facing upstream, the other downstream, the third facing the other 3845).
The first 3845 has a typical packet-size mix (residential/business Internet)
is consistently maxing out at 400 Mbps (predominately ingress because of
asymmetric routing) running at about 43 kpps and 40% CPU.  It's flat-lines
very evenly, uncannily so.  We checked and double-checked transport and it's
set much higher, the same as the second 3845.

The second 3845, which has a mix of both ingress and egress traffic at a
combined 82 kpps (35 kpps ingress/50 kpps egress) but lower combined 360
Mbps operates at a higher CPU (presumably because there's also egress
traffic) with no flatlining.

The ACLs are BCP 38-oriented with eBGP; no rate-limiting.  We're running
124-11.XW2.

Any ideas?  The numbers are well below Cisco's router spec sheet.

Frank