It sounds like your game is getting swapped out so other processes may run a bit, in a noticibly coarse grain - suggesting (to me) that your game is eating up a lot of the CPU. Assuming this is all true, adding the occasional (by which I mean, single, within the body of the game loop) sleep(0) statement or similar may help (e.g. swap out if other processes have a need to execute - note that sleep(0) may be a no-op depending on the exact function called, this is API dependant stuff).

It's not guaranteed to work, but the theory is if other processes get a chance to run more often, chances are they'll have less work to do once they get that chance. It's worth a try, anyways. Chances are this would harm preformance when the user is running (as in, actually running, eating up CPU, not just idling in the background using pagefile space) enough other programs.

All this said, the fact that your example shows a spike to nearly exactly 2.0 (not 1.9 or 2.1) seems a bit fishy, prehaps you've got a bug in your logic code or drivers? Just throwing out suggestions.

Also, since you mention process priorities, I should mention SetPriorityClass. I wouldn't recommend it, but if you want to go down that path, there's information on this functino in The MSDN

HTH

This sounds like another process is taking too long. Certain things seem to do this on certain patforms. I'm developing on Debian linux and for me i notice that web pages open that have any kind of flash/java business on them (like those silly animated flash adverts) will chunkify the framerate. I also notice it when i have my System Monitor open, which monitors active processes (including the game and itself). Ironically, it throws in it's own "hiccup" every 3-4 seconds or so.

I suggest closing every other non-critical application open on your system and seeing if that helps first.