em0, polling performance, P4 2.8ghz FSB 800mhz

[Don Bowman]

 ...
> > 
> > 
> > You may need to increase the MAX_RXD inside your em driver 
> to e.g. 512.
> 
> I didn't know if my card had a buffer bigger than the default 
> 256. I can 
> increase it, but I didn't know how to determine how big a MAX_RXD my 
> card would support. When the system was under load, it was generating 
> 2xHZ clock ticks (2000 when HZ was 1000) is that normal?

max_rxd is not a function of the card. its the system ram
you devote to dma buffers.
Too big will cause problems since it will flush through the 
cache etc.

you should get (vmstat -i) a clk rate that exactly matches
hz.