raw_skew.c

/* CLOCK_MONOTONIC vs CLOCK_MONOTONIC_RAW skew test
 *		by: john stultz (johnstul@us.ibm.com)
 *		    John Stultz <john.stultz@linaro.org>
 *		(C) Copyright IBM 2012
 *		(C) Copyright Linaro Limited 2015
 *		Licensed under the GPLv2
 *
 *  To build:
 *	$ gcc raw_skew.c -o raw_skew -lrt
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/timex.h>
#include <time.h>
#ifdef KTEST
#include "../kselftest.h"
#else
static inline int ksft_exit_pass(void)
{
	exit(0);
}
static inline int ksft_exit_fail(void)
{
	exit(1);
}
#endif


#define CLOCK_MONOTONIC_RAW		4
#define NSEC_PER_SEC 1000000000LL

#define shift_right(x, s) ({		\
	__typeof__(x) __x = (x);	\
	__typeof__(s) __s = (s);	\
	__x < 0 ? -(-__x >> __s) : __x >> __s; \
})

long long llabs(long long val)
{
	if (val < 0)
		val = -val;
	return val;
}

unsigned long long ts_to_nsec(struct timespec ts)
{
	return ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
}

struct timespec nsec_to_ts(long long ns)
{
	struct timespec ts;

	ts.tv_sec = ns/NSEC_PER_SEC;
	ts.tv_nsec = ns%NSEC_PER_SEC;
	return ts;
}

long long diff_timespec(struct timespec start, struct timespec end)
{
	long long start_ns, end_ns;

	start_ns = ts_to_nsec(start);
	end_ns = ts_to_nsec(end);
	return end_ns - start_ns;
}

void get_monotonic_and_raw(struct timespec *mon, struct timespec *raw)
{
	struct timespec start, mid, end;
	long long diff = 0, tmp;
	int i;

	for (i = 0; i < 3; i++) {
		long long newdiff;

		clock_gettime(CLOCK_MONOTONIC, &start);
		clock_gettime(CLOCK_MONOTONIC_RAW, &mid);
		clock_gettime(CLOCK_MONOTONIC, &end);

		newdiff = diff_timespec(start, end);
		if (diff == 0 || newdiff < diff) {
			diff = newdiff;
			*raw = mid;
			tmp = (ts_to_nsec(start) + ts_to_nsec(end))/2;
			*mon = nsec_to_ts(tmp);
		}
	}
}

int main(int argv, char **argc)
{
	struct timespec mon, raw, start, end;
	long long delta1, delta2, interval, eppm, ppm;
	struct timex tx1, tx2;

	setbuf(stdout, NULL);

	if (clock_gettime(CLOCK_MONOTONIC_RAW, &raw)) {
		printf("ERR: NO CLOCK_MONOTONIC_RAW\n");
		return -1;
	}

	tx1.modes = 0;
	adjtimex(&tx1);
	get_monotonic_and_raw(&mon, &raw);
	start = mon;
	delta1 = diff_timespec(mon, raw);

	if (tx1.offset)
		printf("WARNING: ADJ_OFFSET in progress, this will cause inaccurate results\n");

	printf("Estimating clock drift: ");
	sleep(120);

	get_monotonic_and_raw(&mon, &raw);
	end = mon;
	tx2.modes = 0;
	adjtimex(&tx2);
	delta2 = diff_timespec(mon, raw);

	interval = diff_timespec(start, end);

	/* calculate measured ppm between MONOTONIC and MONOTONIC_RAW */
	eppm = ((delta2-delta1)*NSEC_PER_SEC)/interval;
	eppm = -eppm;
	printf("%lld.%i(est)", eppm/1000, abs((int)(eppm%1000)));

	/* Avg the two actual freq samples adjtimex gave us */
	ppm = (tx1.freq + tx2.freq) * 1000 / 2;
	ppm = (long long)tx1.freq * 1000;
	ppm = shift_right(ppm, 16);
	printf(" %lld.%i(act)", ppm/1000, abs((int)(ppm%1000)));

	if (llabs(eppm - ppm) > 1000) {
		printf("	[FAILED]\n");
		return ksft_exit_fail();
	}
	printf("	[OK]\n");
	return  ksft_exit_pass();
}