/*
 * Simple null-syscall latency tester, Ingo Molnar <mingo@redhat.com>
 *
 * Adjust 'OVERHEAD' by hand, it's CPU dependent.
 * (could be done automatically)
 */

#define OVERHEAD 32

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/wait.h>
#include <unistd.h>

static unsigned long long t1, t2;

#define rdtscll(val) \
     __asm__ __volatile__ ("rdtsc;" : "=A" (val))

#define barrier() \
     __asm__ __volatile__ ("lock; addl $0, (%esp);")

int main (void)
{
	unsigned long long min = -1ULL;

	for (;;) {
		barrier();
		rdtscll(t1);
		getpid();
		rdtscll(t2);
		barrier();

		if (t2-t1 < min) {
			min = t2-t1;
			printf(" -> %Ld cycles\n", min-OVERHEAD);
		}
	}
	return 0;
}