ctx.c

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

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

    for (i = 0; i < 10000000; i++) {
        time = __rdtscp(&junk);
        syscall(-1L);
        time = __rdtscp(&junk) - time;
        if (time < min)
            min = time;
    }
    printf("ctx cycles: %d\n", min);

    return 0;
}