clock drift

main.c

#include <stdio.h>
#include <unistd.h>
#include <stdint.h>

inline uint64_t rdtsc() {
    uint32_t low, high;
    __asm__ __volatile__("rdtsc" : "=a"(low), "=d"(high));
    return (uint64_t)low | ((uint64_t)high << 32);
}

int main() {
    int parent = fork();

    int i;
    uint64_t start = rdtsc();
    for(i = 0; i < 20; ++i){
        printf("%s%lu\n", parent ? "\t\t" : "" , rdtsc() - start);
        fflush(stdout);
    }
}