[TriLUG] SMP packet latency question

[Glen Ford]

Using webstone I am generating traffic through an Iptables firewall.
The firewall is a Compaq 580 with two 700mhz cpu.
I can push more packets per second with I remove one of the cpu's.
With one cpu the system is about 80% idle

When I use both cpus, looks like majority of system time is spent
processing interupts
System is about 5% idle
Anyone got any ideas why I am see this behavior?
How I can make the two cpu config process packet as well or better than
single cpu config?

Thanks,
/Glen