rdtsc timing for a measuring a function

Question

I want to time a function call with rdtsc. So I measured it in two ways as follows.

1. Call it in a loop. Aggregate each rdtsc difference within the loop and divi

Answer 1

Have you tried clock_gettime(CLOCK_MONOTONIC, &tp)? Should be quite near to reading the cycle counter by hand, also keep in mind that the cycle counter may not be synchronized between cpu cores.