ctx.c

/*
 * ctx_time Copyright (C) 2018 Matteo Croce <mcroce@redhat.com>
 * a tool measure the context switch time in clock cycles
 */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>
#include <x86intrin.h>

int main (int argc, char *argv[])
{
    int i;
    unsigned long long min = ULLONG_MAX;
    unsigned long long time;
    unsigned junk;

    for (i = 0; i < 10000000; i++) {
        time = __rdtscp(&junk);
        /* a syscalls that does basically nothing but returning a number */
        getuid();
        time = __rdtscp(&junk) - time;

        /* the OS has always better things to do than take care of
         * our benchmarks, get the best value obtained
         */
        if (time < min)
            min = time;
    }
    printf("ctx: %llu clocks\n", min);

    return 0;
}