clock() precision in time.h

Question

I am trying to calculate the number of ticks a function uses to run and to do so an using the clock() function like so:

unsigned long time = clo         


        

Answer 1

Per the clock() manpage, on POSIX platforms the value of the CLOCKS_PER_SEC macro must be 1000000. As you say that the return value you're getting from clock() is a multiple of 10000, that would imply that the resolution is 10 ms.

Also note that clock() on Linux returns an approximation of the processor time used by the program. On Linux, again, scheduler statistics are updated when the scheduler runs, at CONFIG_HZ frequency. So if the periodic timer tick is 100 Hz, you get process CPU time consumption statistics with 10 ms resolution.

Walltime measurements are not bound by this, and can be much more accurate. clock_gettime(CLOCK_MONOTONIC, ...) on a modern Linux system provides nanosecond resolution.