High interrupt rate

[b. f.]

>
> I know 75% idle is not bad but this machine, when not under load on a saturday
> night like today, used to be at around 98% idle 99% of the time. Now its is at
> 72% idle 99.9% of the time. It has been like this all day.
>
> The only things with a high interrupt rate are
>
> cpu0: timer                     46922025       2000
> cpu1: timer                     46918117       1999
>
> What could be causing this?

I don't know that 2 timer interrupts per-cpu, per kern.hz, is
altogether unexpected for some configurations, under some conditions.
What happens if you boot with kern.hz="100" in /boot/loader.conf, or
set via the loader command line?  What happens if you remove the
DEVICE_POLLING option from your kernel (and _not_ just disable polling
per-device)?  What is the output from "sysctl kern.timecounter
kern.eventtimer"?

b.