tsc.c

#include <stdint.h>
#include <time.h>
#include <sys/time.h>

#include "xgbc.h"

#define DURATION_US 10000ULL

uint32_t determine_tsc_resolution(void)
{
    uint32_t resolutions[10];

    for (int i = 0; i < 10; i++)
    {
        uint64_t rdtsc_start, rdtsc_end, duration;
        struct timeval tv1, tv2;

        __asm__ __volatile__ ("" ::: "memory");

        gettimeofday(&tv1, NULL);
        __asm__ __volatile__ ("rdtsc" : "=A"(rdtsc_start));
        nanosleep(&(struct timespec){ .tv_nsec = DURATION_US * 1000 }, NULL);
        gettimeofday(&tv2, NULL);
        __asm__ __volatile__ ("rdtsc" : "=A"(rdtsc_end));

        __asm__ __volatile__ ("" ::: "memory");

        duration = (uint64_t)(tv2.tv_usec - tv1.tv_usec) + (uint64_t)(tv2.tv_sec - tv1.tv_sec) * 1000000ULL;
        resolutions[i] = (rdtsc_end - rdtsc_start) * 1000 / duration;
    }

    uint64_t sum = 0;
    uint32_t max = 0, min = 0xFFFFFFFF;
    for (int i = 0; i < 10; i++)
    {
        if (resolutions[i] < min)
            min = resolutions[i];
        if (resolutions[i] > max)
            max = resolutions[i];
        sum += (uint64_t)resolutions[i];
    }

    sum -= min + max;

    sum /= 8;

    return sum;
}