timers, kselftest: Add 'adjtick' test to validate adjtimex() tick adjustments

Recently a kernel side NTP bug was fixed via the following commit:

2619d7e9c92d ("time: Fix timekeeping_freqadjust()'s incorrect use of abs() instead of abs64()")

When the bug was reported it was difficult to detect, except by
tweaking the adjtimex tick value, and noticing how quickly the
adjustment took:

https://lkml.org/lkml/2015/9/1/488

Thus this patch introduces a new test which manipulates the
adjtimex tick value and validates that the results are what we
expect.

Signed-off-by: John Stultz <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Miroslav Lichvar <[e-mail]>
Cc: Nuno Gonçalves <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Prarit Bhargava <[e-mail]>
Cc: Richard Cochran <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
[ Tidied up the code and the changelog a bit. ]
Signed-off-by: Ingo Molnar <[e-mail]>

tools/testing/selftests/timers/Makefile

···
 TEST_PROGS = posix_timers nanosleep nsleep-lat set-timer-lat mqueue-lat \
 	     inconsistency-check raw_skew threadtest rtctest
 
-TEST_PROGS_EXTENDED = alarmtimer-suspend valid-adjtimex change_skew \
+TEST_PROGS_EXTENDED = alarmtimer-suspend valid-adjtimex adjtick change_skew \
 		      skew_consistency clocksource-switch leap-a-day \
 		      leapcrash set-tai set-2038
 
···
 run_destructive_tests: run_tests
 	./alarmtimer-suspend
 	./valid-adjtimex
+	./adjtick
 	./change_skew
 	./skew_consistency
 	./clocksource-switch

tools/testing/selftests/timers/adjtick.c

···
+/* adjtimex() tick adjustment test
+ *		by:   John Stultz <[e-mail]>
+ *		(C) Copyright Linaro Limited 2015
+ *		Licensed under the GPLv2
+ *
+ *  To build:
+ *	$ gcc adjtick.c -o adjtick -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 USEC_PER_SEC		1000000
+
+#define MILLION			1000000
+
+long systick;
+
+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;
+
+	clock_gettime(CLOCK_MONOTONIC, mon);
+	clock_gettime(CLOCK_MONOTONIC_RAW, raw);
+
+	/* Try to get a more tightly bound pairing */
+	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);
+		}
+	}
+}
+
+long long get_ppm_drift(void)
+{
+	struct timespec mon_start, raw_start, mon_end, raw_end;
+	long long delta1, delta2, eppm;
+
+	get_monotonic_and_raw(&mon_start, &raw_start);
+
+	sleep(15);
+
+	get_monotonic_and_raw(&mon_end, &raw_end);
+
+	delta1 = diff_timespec(mon_start, mon_end);
+	delta2 = diff_timespec(raw_start, raw_end);
+
+	eppm = (delta1*MILLION)/delta2 - MILLION;
+
+	return eppm;
+}
+
+int check_tick_adj(long tickval)
+{
+	long long eppm, ppm;
+	struct timex tx1;
+
+	tx1.modes	 = ADJ_TICK;
+	tx1.modes	|= ADJ_OFFSET;
+	tx1.modes	|= ADJ_FREQUENCY;
+	tx1.modes	|= ADJ_STATUS;
+
+	tx1.status	= STA_PLL;
+	tx1.offset	= 0;
+	tx1.freq	= 0;
+	tx1.tick	= tickval;
+
+	adjtimex(&tx1);
+
+	sleep(1);
+
+	ppm = ((long long)tickval * MILLION)/systick - MILLION;
+	printf("Estimating tick (act: %ld usec, %lld ppm): ", tickval, ppm);
+
+	eppm = get_ppm_drift();
+	printf("%lld usec, %lld ppm", systick + (systick * eppm / MILLION), eppm);
+
+	tx1.modes = 0;
+	adjtimex(&tx1);
+
+	if (tx1.offset || tx1.freq || tx1.tick != tickval) {
+		printf("	[ERROR]\n");
+		printf("\tUnexpected adjtimex return values, make sure ntpd is not running.\n");
+		return -1;
+	}
+
+	/*
+	 * Here we use 100ppm difference as an error bound.
+	 * We likely should see better, but some coarse clocksources
+	 * cannot match the HZ tick size accurately, so we have a
+	 * internal correction factor that doesn't scale exactly
+	 * with the adjustment, resulting in > 10ppm error during
+	 * a 10% adjustment. 100ppm also gives us more breathing
+	 * room for interruptions during the measurement.
+	 */
+	if (llabs(eppm - ppm) > 100) {
+		printf("	[FAILED]\n");
+		return -1;
+	}
+	printf("	[OK]\n");
+
+	return  0;
+}
+
+int main(int argv, char **argc)
+{
+	struct timespec raw;
+	long tick, max, interval, err;
+	struct timex tx1;
+
+	err = 0;
+	setbuf(stdout, NULL);
+
+	if (clock_gettime(CLOCK_MONOTONIC_RAW, &raw)) {
+		printf("ERR: NO CLOCK_MONOTONIC_RAW\n");
+		return -1;
+	}
+
+	printf("Each iteration takes about 15 seconds\n");
+
+	systick = sysconf(_SC_CLK_TCK);
+	systick = USEC_PER_SEC/sysconf(_SC_CLK_TCK);
+	max = systick/10; /* +/- 10% */
+	interval = max/4; /* in 4 steps each side */
+
+	for (tick = (systick - max); tick < (systick + max); tick += interval) {
+		if (check_tick_adj(tick)) {
+			err = 1;
+			break;
+		}
+	}
+
+	/* Reset things to zero */
+	tx1.modes	 = ADJ_TICK;
+	tx1.modes	|= ADJ_OFFSET;
+	tx1.modes	|= ADJ_FREQUENCY;
+
+	tx1.offset	 = 0;
+	tx1.freq	 = 0;
+	tx1.tick	 = systick;
+
+	adjtimex(&tx1);
+
+	if (err)
+		return ksft_exit_fail();
+
+	return ksft_exit_pass();
+}