This is related to intel speedstep/eist/c1e and how windows 8.1 misuses it.
I thought I should disable as many variables as possible, and went into the bios and disabled speedstep. The cpu locks to a fixed speed, and the periodic issues go away. Of course I can't keep it this way except for testing. Most of the time I use the laptop for regular work and not gaming, and I like some battery time.
FOLLOWUP QUESTION: does anyone know of any good custom thermal / speedstep/eist/c1e control software for windows 8.1?
However. I don't understand why it was behaving this way to begin with. I had the same issues regardless of which windows power management settings I used. The games don't use much cpu power and the cpu was idling most of the time. Exception was portal2 when running with vertical sync and fps cap off.
In power control options:
Tried "fixed" (same min/max) cpu speed. At various speeds ranging from 0.7GHz to 2.7GHz
Tried cooling policy passive / active.
Tried graphics performance max/min.
Same issues all the time regardless of power management settings. The laptop was always very cool, never got warm. Even when set to high "fixed" cpu speed and active cooling the fan almost never even turned on.
So, this brings me to the followup questions: How can I change the cpu/thermal regulation in win8.1? Any good custom control software out there? Or how to actually make the power control behave.