How to measure the ACTUAL execution time of a C program under Linux?

c, linux, time

Solution

You can check the real CPU time of a process on linux by utilizing the CPU Time functionality of the kernel:

 #include <time.h>

 clock_t start, end;
 double cpu_time_used;

 start = clock();
 ... /* Do the work. */
 end = clock();
 cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;

Source: http://www.gnu.org/s/hello/manual/libc/CPU-Time.html#CPU-Time

That way, you count the CPU ticks or the real amount of instructions worked upon by the CPU on the process, thus getting the real amount of work time.

Problem

I know this question may have been commonly asked before, but it seems most of those questions are regarding the elapsed time (based on wall clock) of a piece of code. The elapsed time of a piece of code is unlikely equal to the actual execution time, as other processes may be executing during the elapsed time of the code of interest. I used getrusage() to get the user time and system time of a process, and then calculate the actual execution time by (user time + system time). I am running my program on Ubuntu. Here are my questions: - How do I know the precision of getrusage()? - Are there other approaches that can provide higher precision than getrusage()?

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