#define _GNU_SOURCE
#include <errno.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <sys/mman.h>
#include <sys/time.h>
#include <sys/wait.h>

struct time_exit {
	volatile int ready	__attribute__((aligned(64)));
	volatile int quit	__attribute__((aligned(64)));
};

#define cpu_relax()             asm volatile ("rep;nop":::"memory");

#define MAXCPUS 4096
static int cpu_set_size;
static cpu_set_t *task_affinity;
static int delay;

static void pin(int cpu)
{
	cpu_set_t *affinity;

	if (cpu < 0 || cpu >= MAXCPUS)
		return;

	affinity = CPU_ALLOC(MAXCPUS);
	CPU_ZERO_S(cpu_set_size, affinity);
	CPU_SET_S(cpu, cpu_set_size, affinity);
	(void)sched_setaffinity(0, cpu_set_size, affinity);
	CPU_FREE(affinity);
	return;
}

static void child(struct time_exit *sharep, int cpu)
{
	pin(cpu);
	__sync_fetch_and_add(&sharep->ready, 1);
	while (sharep->quit == 0)
		cpu_relax();
	exit(0);
}

int main(int argc, char **argv)
{
	int children, i;
	struct time_exit *sharep;
	struct timeval tv0, tv1;
	long secs, usecs;
	char opt;

	while ((opt = getopt(argc, argv, "p:")) != -1) {
		switch (opt) {
		case 'p':
			delay = atoi(optarg);
			break;
		default:
			fprintf(stderr, "Usage:\n");
		}
	}
	argv += optind - 1;
	argc -= optind - 1;
	if (argc != 2) {
		printf("Wrong\n");
		exit(-1);
	}
	children = atoi(argv[1]);

	cpu_set_size = CPU_ALLOC_SIZE(MAXCPUS);
	task_affinity = CPU_ALLOC(MAXCPUS);
	if (sched_getaffinity(0, cpu_set_size, task_affinity) < 0) {
		perror("Failed in sched_getaffinitt");
		exit(-2);
	}

	sharep = mmap(0, sizeof(struct time_exit), PROT_READ | PROT_WRITE,
			MAP_ANONYMOUS | MAP_SHARED, -1, 0);

	for (i = 0; i < children; i++)
		if (fork() == 0)
			child(sharep, i);

	while (sharep->ready != children)
		cpu_relax();

	if (delay)
		sleep(delay);

	gettimeofday(&tv0, NULL);
	sharep->quit = 1;
	while (wait(&i) > 0)
		cpu_relax();
	gettimeofday(&tv1, NULL);

	usecs = tv1.tv_usec - tv0.tv_usec;
	secs = tv1.tv_sec - tv0.tv_sec;
	if (usecs < 0) {
		secs--;
		usecs += 1000000;
	}
	printf("%7ld.%06ld\n", secs, usecs);

	return 0;
}