iperf results not good: 31% system, 69% interrupt, 0% idle!

[Kent Watsen]

I just installed a Netgear GA311 (re) into a 500MHz Netra T1 running 4.2 
(sparc64)

Running `iperf -s` on it shows only 187 Mbits/sec, which surprised me 
because other iperf-targets plugged into same switch show ~600 Mbits/sec

Looking at `top` shows why: 31% system, 69% interrupt, 0% idle  and the 
iperf process 25% CPU

What is going on? - is the re driver not good?

Thanks!
Kent