> But on the other hand if I keep the interrupts to a minimum then the NetBSD 
> kernel is somehow relative predicatble in terms of guaranteed interrupt 
> service, right?

Only at the higher interrupt levels. The lower interrupt levels are frequently
blocked for mutual exclusion purposes, whether or not any interrupts actually
occur, simply because if you don't do this and the interrupt DOES occur,
you're screwed.

If you reconfigured your kernel so that some classes of interrupts simply
couldn't be requested any more, then you could alter the kernel mutual
exclusion code to not raise the interrupt level when it's no longer
necessary. But this is a pretty invasive operation and you can easily
build yourself a flaky kernel if you do it wrong.

But yes, if you took this far enough, you'd have nothing but the raw CPU
instruction and interrupt processing latency to deal with.

Todd Whitesel
toddpw @ best.com