I'm not sure how what you describe is any different than focusing on the critical parts of the program. If a function is short but is called many many times, th

I'm not sure how what you describe is any different than focusing on the critical parts of the program. If a function is short but is called many many times, that could still be a hot spot. It's also worth noting that even then, it still may not matter if you're stalled out on something like I/O or whatever (while still keeping in mind other constraints like battery life, CPU throttling, etc).