#include <stdio.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <time.h>
#include <math.h>
#include <stdlib.h>
#include <unistd.h>

#define NR_ALPHAS	('z' - 'a' + 1)

int main(int argc, char **argv)
{
	struct timespec intv_ts = { }, ts;
	unsigned long long time0, time1;
	long long msecs = 10;
	const size_t map_size = 4096 * 4;

	if (argc > 1) {
		msecs = atoll(argv[1]);
		if (msecs <= 0) {
			fprintf(stderr, "test-latency [interval-in-msecs]\n");
			return 1;
		}
	}

	intv_ts.tv_sec = msecs / 1000;
	intv_ts.tv_nsec = (msecs % 1000) * 1000000;

	clock_gettime(CLOCK_MONOTONIC, &ts);
	time1 = ts.tv_sec * 1000000000LLU + ts.tv_nsec;

	while (1) {
		void *map, *p;
		int idx;
		char c;

		nanosleep(&intv_ts, NULL);
		map = mmap(NULL, map_size, PROT_READ | PROT_WRITE,
			   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
		if (map == MAP_FAILED) {
			perror("mmap");
			return 1;
		}

		for (p = map; p < map + map_size; p += 4096)
			*(volatile unsigned long *)p = 0xdeadbeef;

		munmap(map, map_size);

		time0 = time1;
		clock_gettime(CLOCK_MONOTONIC, &ts);
		time1 = ts.tv_sec * 1000000000LLU + ts.tv_nsec;

		idx = (time1 - time0) / msecs / 1000000;
		idx = log2(idx);
		if (idx <= 1) {
			c = '.';
		} else {
			if (idx > 9)
				idx = 9;
			c = '0' + idx;
		}
		write(1, &c, 1);
	}
}