On: What Does the OS X Activity Monitor’s “Energy Impa...

[nnethercote]

If you poll with high frequency you'll be causing lots of additional wake-ups which will badly skew what you're measuring.

[pjc50 → nnethercote]

Ideally you'd do an accounting update on task switch, along with all the other housekeeping. Then you don't need to do any polling. There's a "process accounting" infrastructure which perhaps could be adapted for this.