Packet loss problem.

[Alex A. Pavlenko]

Hi,

I'm not quite sure if it is write list for this question, so please forgive
me if it is really so.
The background is as follows.
Hardware is HP Proliant DL380 G5 server with 2  3Ghz Xeon CPUs and 2
on-board Broadcom NICs(bge).
Software - FreeBSD 6.2-STABLE, pf, ipfw+DUMMYNET. 
  The only job for this server is to provide NAT(pf) and
traffic-shape(dummynet) services for customers. 
It works fine while summary packet rate of incoming packets on both
interfaces is no more than about 
50 Kpps. With higher rates it starts to loose packets, 2% and more depending
on incoming network traffic.
At this time net.inet.ip.intr_queue_drops counter increases very fast, a few
thousands per second.
What I can not understand is that at the same time CPU load dedicated to
interrupts is about 30%.
The rest is dedicated to CPU idle state according to `top` command. I'm not
the OS guru so I can
interpret statistics above incorrectly, but my assumption is that OS uses
only 1 of  4 CPUs cores to process
incoming packets, other three cores perform a small amount of other system
jobs.
So what I would like to ask you is to give the right explanation for such
behaviour. 
Also any suggestions to improve performance would be great since this
service is very critical
for our company.
Thank you very much for any responses.

--
Alex.