Question

I have following code snippet and i am trying to evaluate the time take by CPU

However I am getting some weird results

struct timeval begin, end;
double cpu_time=0.0;
gettimeofday(&begin, NULL);
long cpu_sum = 0;


for (i = 0; i < size; i++) {
 cpu_sum += array[i] * array[i];
}    
 gettimeofday(&end, NULL);
 cpu_time = end.tv_sec - begin.tv_sec * 1000;
 cpu_time += (end.tv_usec - begin.tv_usec) / 1000;

 printf("calculated sum: %d using CPU in %lf ms \n", cpu_sum, cpu_time);

Sample result = 1296217442.000000 ms

I dont think this is correct time value in ms.
Can anyone help whats wrong here?

Any help would be appreciated.

Thanks

Answer 1

If you want CPU time, you probably want to use clock_gettime instead with the CLOCK_PROCESS_CPUTIME_ID parameter.

That’s the probably most convenient (and accurate) way to get both real time and cpu time using the same function, only changing one parameter.