rdtsc demo

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() {
        fork();

        uint64_t count = rdtsc();
        for (int i = 0; i < 100000; ++i)
                usleep(1);
        printf("%d: %llu\n", getpid(), rdtsc() - count);
}

Makefile

all:
        gcc -std=c99 -O1 main.c