Intel RDTSC (Read Timestamp Counter) Instruction

main.c

#include <stdio.h>

#include "rdtsc.h"

int main(int argc, char *argv[]) {
    uint64_t timestamp[10000];
    uint64_t diff;
    int i;
    for (i = 0; i < 10000; i++) {
        timestamp[i] = rdtsc();
    }
    for (i = 1; i < 10000; i++) {
        diff = timestamp[i] - timestamp[i-1];
        printf("%lu\n", diff);
    }       
    return 0;
}

Makefile

main: main.c

.PHONY:
clean:
	rm -f main

rdtsc.h

#ifndef __RDTSC_H__
#define __RDTSC_H__

#ifdef __cplusplus
#include <cstdint>
#else
#include <stdint.h>
#endif

#ifdef __cplusplus
extern "C" {
#endif

__inline__ uint64_t rdtsc(void) {
    uint32_t lo;
    uint32_t hi;
    __asm__ __volatile__ (      // serialize
    "xorl %%eax,%%eax \n        cpuid"
    ::: "%rax", "%rbx", "%rcx", "%rdx");
    /* We cannot use "=A", since this would use %rax on x86_64 and return only the lower 32bits of the TSC */
    __asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
    return (uint64_t)hi << 32 | lo;
}

#ifdef __cplusplus
}
#endif

#endif