Compute cpu frequency. This works because lines 12-17 are dependent operations which can't be pipelined and so must take 10 cycles.

cpu.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
 
 
// Perform CYCLES simple in-order operations
unsigned loop(int CYCLES)
{
    unsigned a = rand(),  b = rand(),  x = rand();
    for (int i=0; i < CYCLES/10; i++)
    {
        x = (x + a) ^ b;
        x = (x + a) ^ b;
        x = (x + a) ^ b;
        x = (x + a) ^ b;
        x = (x + a) ^ b;
    }
    return x;
}
 
int main(int argc, char *argv[])
{
    int CYCLES = 1000*1000*1000;
    unsigned x = loop(CYCLES/10);  // warm up the cpu
 
    struct timeval tm, tn;
    gettimeofday(&tm, NULL);
 
    x += loop(CYCLES);
 
    gettimeofday(&tn, NULL);
    double t1 = (tn.tv_sec - tm.tv_sec) +
                (tn.tv_usec - tm.tv_usec) / 1e6;
 
    if (x)
        printf("Time: %.6f s, CPU freq %.2f GHz\n", t1, (CYCLES/1e9)/t1);
    return 0;
}