Device polling question - Freebsd 4.9

[TM4525 at aol.com]

I'm a bit confused about device polling. I put a counter in em_poll(), and 
then enabled device polling for 10 seconds and read back the counter, and it was 
called 1.5million times. This is with virtually no network activity and HZ 
set to the default of 100.

The docs seem to imply that the polling function gets called once per clock 
tick, but that doesn't seem to be the case at all. I'm trying to figure the 
reasoning behind mucking with the HZ value, which may affect some other things 
and also seems to defeat the purpose of trying to reduce overhead.

With the HZ value at 100 the system easily passes 90K pps, but Im concerned 
about what variations occur when the system is under load, or if there are 
time-consuming activities (like extensive firewall rules).

Also, when using device polling, even under heavy network load "top" shows 
the system to be almost completely idle. How can I gauge system usage when using 
polling instead of interrupts? Its difficult to compare the 2 methods when 
one of them can't be measured.

TIA

Tommy Mato