[PATCH v4] kselftest: timers: Add adjtick test to validate adjtimex() tick adjustments

[John Stultz]

Recently an issue was reported that was difficult to detect except
by tweaking the adjtimex tick value, and noticing how quickly the
adjustment took to be made:
	https://lkml.org/lkml/2015/9/1/488

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

Cc: Nuno GonÃalves <nunojpg@xxxxxxxxx>
Cc: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Richard Cochran <richardcochran@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
v2: - Use sysconf(_SC_CLK_TCK) to properly get USER_HZ value.
v3: - Set STA_PLL to ensure offset is cleared
    - Add rational for 100ppm error bound
v4: - Add message informing each iteration takes ~15 secs
    - Cleanup error message when ntpd is suspected of running

 tools/testing/selftests/timers/Makefile  |   3 +-
 tools/testing/selftests/timers/adjtick.c | 210 +++++++++++++++++++++++++++++++
 2 files changed, 212 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/timers/adjtick.c

diff --git a/tools/testing/selftests/timers/Makefile b/tools/testing/selftests/timers/Makefile
index 89a3f44..4a1be1b 100644
--- a/tools/testing/selftests/timers/Makefile
+++ b/tools/testing/selftests/timers/Makefile
@@ -8,7 +8,7 @@ LDFLAGS += -lrt -lpthread
 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
 
@@ -24,6 +24,7 @@ include ../lib.mk
 run_destructive_tests: run_tests
 	./alarmtimer-suspend
 	./valid-adjtimex
+	./adjtick
 	./change_skew
 	./skew_consistency
 	./clocksource-switch
diff --git a/tools/testing/selftests/timers/adjtick.c b/tools/testing/selftests/timers/adjtick.c
new file mode 100644
index 0000000..253f684
--- /dev/null
+++ b/tools/testing/selftests/timers/adjtick.c
@@ -0,0 +1,210 @@
+/* adjtimex() tick adjustment test
+ *		by:   John Stultz <john.stultz@xxxxxxxxxx>
+ *		(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();
+}
-- 
1.9.1

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