polling(4) and idle time/cpu usage percentages

[Kevin Day]

I've got a FreeBSD system acting as a router, it's passing 250-600mbps of 
traffic through it most of the time.

Yesterday it was running 4.6-RELEASE without polling. I've upgraded it to 
4.8 and enabled polling. Before it was showing 30-50% CPU use in interrupt 
and system combined. Now it's showing 0-1% (99% idle).

Is this because it's polling in the idle loop, and time spent doing this 
isn't getting accounted for anywhere, or is polling THAT much more efficient?

If it's the former, is it supposed to work this way? Now I've got no clear 
way of knowing how busy the system is. (It's just routing packets, really 
nothing more)

-- Kevin