> The main issue with RDTSC is that task-switches may cause your thread of execution to change cores or mess up your timing Task switches messing with timing,

> The main issue with RDTSC is that task-switches may cause your thread of execution to change cores or mess up your timing Task switches messing with timing, yes. Changing cores, on the other hand, is not so much of a problem by itself anymore. I'm pretty sure recent Intel CPUs guarantee that rdtsc is synchronized across cores.