#include <errno.h>
#include <stdio.h>
#include <sched.h>
#include <signal.h>
#include <sys/io.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/unistd.h>

#define CYCLES(x) asm volatile ("rdtsc" :"=a" (x)::"edx")

#define __NR_sched_set_affinity 241
_syscall3 (int, sched_set_affinity, pid_t, pid, unsigned int, mask_len, unsigned long *, mask)

/*
 * Use a pair of RT processes bound to the same CPU to measure
 * context-switch overhead:
 */
static void measure(void)
{
	unsigned long i, min = ~0UL, mask = 1, t1, t2;

	sched_yield();
	for (i = 0; i < 100; i++) {
		asm volatile ("sti; nop; cli");
		CYCLES(t1);
		sched_yield();
		CYCLES(t2);
		if (i > 10) {
			if (t2 - t1 < min)
				min = t2 - t1;
		}
	}
	asm volatile ("sti");

	printf("scheduling latency: %ld cycles\n", min);
	sched_yield();
}

int main(void)
{
	struct sched_param p = { sched_priority: 2 };
	unsigned long mask = 1, pid;

	if (iopl(3)) {
		printf("need to run as root!\n");
		exit(-1);
	}
	sched_setscheduler(0, SCHED_FIFO, &p);
	sched_set_affinity(0, sizeof(mask), &mask);

	pid = fork();
	if (!pid)
		for (;;) {
			asm volatile ("sti; nop; cli");
			sched_yield();
		}

	printf("default no ioperm:             ");
	measure();

	printf("turning on port 80 ioperm:     ");
	ioperm(0x80,1,1);
	measure();

	printf("turning on port 65535 ioperm:  ");
	if (ioperm(0xffff,1,1))
		printf("FAILED - older kernel.\n");
	else
		measure();
	kill(pid, 9);

	return 0;
}