I've "investigated" this a number of times and landed in CACurrentMediaTime which if I remember correctly is essentially a wrapper around mach_absolute_time(), doing the conversion from CPU ticks to seconds for you, and thereby being some fraction of a microsecond slower than mach_absolute_time(). But I'm happy to change my habit if there's a problem with it. I doubt that the efficiency and/or accuracy of the timing function would make much difference in this particular case though. According to my experience, optimization glitches depending on seemingly unrelated context in various crazy ways is still much more of an issue in this type of benchmarking.