kselftests: timers: Add test for frequency step

This test checks the response of the system clock to frequency
steps made with adjtimex(). The frequency error and stability of
the CLOCK_MONOTONIC clock relative to the CLOCK_MONOTONIC_RAW clock
is measured in two intervals following the step. The test fails if
values from the second interval exceed specified limits.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

tools/testing/selftests/timers/Makefile

 BUILD_FLAGS = -DKTEST
 CFLAGS += -O3 -Wl,-no-as-needed -Wall $(BUILD_FLAGS)
-LDFLAGS += -lrt -lpthread
+LDFLAGS += -lrt -lpthread -lm
 
 # these are all "safe" tests that don't modify
 # system time or require escalated privileges
@@ -8,7 +8,7 @@ TEST_GEN_PROGS = posix_timers nanosleep nsleep-lat set-timer-lat mqueue-lat \
 	     inconsistency-check raw_skew threadtest rtctest
 
 TEST_GEN_PROGS_EXTENDED = alarmtimer-suspend valid-adjtimex adjtick change_skew \
-		      skew_consistency clocksource-switch leap-a-day \
+		      skew_consistency clocksource-switch freq-step leap-a-day \
 		      leapcrash set-tai set-2038 set-tz
 
 
@@ -24,6 +24,7 @@ run_destructive_tests: run_tests
 	./change_skew
 	./skew_consistency
 	./clocksource-switch
+	./freq-step
 	./leap-a-day -s -i 10
 	./leapcrash
 	./set-tz

tools/testing/selftests/timers/freq-step.c

+/*
+ * This test checks the response of the system clock to frequency
+ * steps made with adjtimex(). The frequency error and stability of
+ * the CLOCK_MONOTONIC clock relative to the CLOCK_MONOTONIC_RAW clock
+ * is measured in two intervals following the step. The test fails if
+ * values from the second interval exceed specified limits.
+ *
+ * Copyright (C) Miroslav Lichvar <mlichvar@redhat.com>  2017
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * 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 <math.h>
+#include <stdio.h>
+#include <sys/timex.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+#define SAMPLES 100
+#define SAMPLE_READINGS 10
+#define MEAN_SAMPLE_INTERVAL 0.1
+#define STEP_INTERVAL 1.0
+#define MAX_PRECISION 100e-9
+#define MAX_FREQ_ERROR 10e-6
+#define MAX_STDDEV 1000e-9
+
+struct sample {
+	double offset;
+	double time;
+};
+
+static time_t mono_raw_base;
+static time_t mono_base;
+static long user_hz;
+static double precision;
+static double mono_freq_offset;
+
+static double diff_timespec(struct timespec *ts1, struct timespec *ts2)
+{
+	return ts1->tv_sec - ts2->tv_sec + (ts1->tv_nsec - ts2->tv_nsec) / 1e9;
+}
+
+static double get_sample(struct sample *sample)
+{
+	double delay, mindelay = 0.0;
+	struct timespec ts1, ts2, ts3;
+	int i;
+
+	for (i = 0; i < SAMPLE_READINGS; i++) {
+		clock_gettime(CLOCK_MONOTONIC_RAW, &ts1);
+		clock_gettime(CLOCK_MONOTONIC, &ts2);
+		clock_gettime(CLOCK_MONOTONIC_RAW, &ts3);
+
+		ts1.tv_sec -= mono_raw_base;
+		ts2.tv_sec -= mono_base;
+		ts3.tv_sec -= mono_raw_base;
+
+		delay = diff_timespec(&ts3, &ts1);
+		if (delay <= 1e-9) {
+			i--;
+			continue;
+		}
+
+		if (!i || delay < mindelay) {
+			sample->offset = diff_timespec(&ts2, &ts1);
+			sample->offset -= delay / 2.0;
+			sample->time = ts1.tv_sec + ts1.tv_nsec / 1e9;
+			mindelay = delay;
+		}
+	}
+
+	return mindelay;
+}
+
+static void reset_ntp_error(void)
+{
+	struct timex txc;
+
+	txc.modes = ADJ_SETOFFSET;
+	txc.time.tv_sec = 0;
+	txc.time.tv_usec = 0;
+
+	if (adjtimex(&txc) < 0) {
+		perror("[FAIL] adjtimex");
+		ksft_exit_fail();
+	}
+}
+
+static void set_frequency(double freq)
+{
+	struct timex txc;
+	int tick_offset;
+
+	tick_offset = 1e6 * freq / user_hz;
+
+	txc.modes = ADJ_TICK | ADJ_FREQUENCY;
+	txc.tick = 1000000 / user_hz + tick_offset;
+	txc.freq = (1e6 * freq - user_hz * tick_offset) * (1 << 16);
+
+	if (adjtimex(&txc) < 0) {
+		perror("[FAIL] adjtimex");
+		ksft_exit_fail();
+	}
+}
+
+static void regress(struct sample *samples, int n, double *intercept,
+		    double *slope, double *r_stddev, double *r_max)
+{
+	double x, y, r, x_sum, y_sum, xy_sum, x2_sum, r2_sum;
+	int i;
+
+	x_sum = 0.0, y_sum = 0.0, xy_sum = 0.0, x2_sum = 0.0;
+
+	for (i = 0; i < n; i++) {
+		x = samples[i].time;
+		y = samples[i].offset;
+
+		x_sum += x;
+		y_sum += y;
+		xy_sum += x * y;
+		x2_sum += x * x;
+	}
+
+	*slope = (xy_sum - x_sum * y_sum / n) / (x2_sum - x_sum * x_sum / n);
+	*intercept = (y_sum - *slope * x_sum) / n;
+
+	*r_max = 0.0, r2_sum = 0.0;
+
+	for (i = 0; i < n; i++) {
+		x = samples[i].time;
+		y = samples[i].offset;
+		r = fabs(x * *slope + *intercept - y);
+		if (*r_max < r)
+			*r_max = r;
+		r2_sum += r * r;
+	}
+
+	*r_stddev = sqrt(r2_sum / n);
+}
+
+static int run_test(int calibration, double freq_base, double freq_step)
+{
+	struct sample samples[SAMPLES];
+	double intercept, slope, stddev1, max1, stddev2, max2;
+	double freq_error1, freq_error2;
+	int i;
+
+	set_frequency(freq_base);
+
+	for (i = 0; i < 10; i++)
+		usleep(1e6 * MEAN_SAMPLE_INTERVAL / 10);
+
+	reset_ntp_error();
+
+	set_frequency(freq_base + freq_step);
+
+	for (i = 0; i < 10; i++)
+		usleep(rand() % 2000000 * STEP_INTERVAL / 10);
+
+	set_frequency(freq_base);
+
+	for (i = 0; i < SAMPLES; i++) {
+		usleep(rand() % 2000000 * MEAN_SAMPLE_INTERVAL);
+		get_sample(&samples[i]);
+	}
+
+	if (calibration) {
+		regress(samples, SAMPLES, &intercept, &slope, &stddev1, &max1);
+		mono_freq_offset = slope;
+		printf("CLOCK_MONOTONIC_RAW frequency offset: %11.3f ppm\n",
+		       1e6 * mono_freq_offset);
+		return 0;
+	}
+
+	regress(samples, SAMPLES / 2, &intercept, &slope, &stddev1, &max1);
+	freq_error1 = slope * (1.0 - mono_freq_offset) - mono_freq_offset -
+			freq_base;
+
+	regress(samples + SAMPLES / 2, SAMPLES / 2, &intercept, &slope,
+		&stddev2, &max2);
+	freq_error2 = slope * (1.0 - mono_freq_offset) - mono_freq_offset -
+			freq_base;
+
+	printf("%6.0f %+10.3f %6.0f %7.0f %+10.3f %6.0f %7.0f\t",
+	       1e6 * freq_step,
+	       1e6 * freq_error1, 1e9 * stddev1, 1e9 * max1,
+	       1e6 * freq_error2, 1e9 * stddev2, 1e9 * max2);
+
+	if (fabs(freq_error2) > MAX_FREQ_ERROR || stddev2 > MAX_STDDEV) {
+		printf("[FAIL]\n");
+		return 1;
+	}
+
+	printf("[OK]\n");
+	return 0;
+}
+
+static void init_test(void)
+{
+	struct timespec ts;
+	struct sample sample;
+
+	if (clock_gettime(CLOCK_MONOTONIC_RAW, &ts)) {
+		perror("[FAIL] clock_gettime(CLOCK_MONOTONIC_RAW)");
+		ksft_exit_fail();
+	}
+
+	mono_raw_base = ts.tv_sec;
+
+	if (clock_gettime(CLOCK_MONOTONIC, &ts)) {
+		perror("[FAIL] clock_gettime(CLOCK_MONOTONIC)");
+		ksft_exit_fail();
+	}
+
+	mono_base = ts.tv_sec;
+
+	user_hz = sysconf(_SC_CLK_TCK);
+
+	precision = get_sample(&sample) / 2.0;
+	printf("CLOCK_MONOTONIC_RAW+CLOCK_MONOTONIC precision: %.0f ns\t\t",
+	       1e9 * precision);
+
+	if (precision > MAX_PRECISION) {
+		printf("[SKIP]\n");
+		ksft_exit_skip();
+	}
+
+	printf("[OK]\n");
+	srand(ts.tv_sec ^ ts.tv_nsec);
+
+	run_test(1, 0.0, 0.0);
+}
+
+int main(int argc, char **argv)
+{
+	double freq_base, freq_step;
+	int i, j, fails = 0;
+
+	init_test();
+
+	printf("Checking response to frequency step:\n");
+	printf("  Step           1st interval              2nd interval\n");
+	printf("             Freq    Dev     Max       Freq    Dev     Max\n");
+
+	for (i = 2; i >= 0; i--) {
+		for (j = 0; j < 5; j++) {
+			freq_base = (rand() % (1 << 24) - (1 << 23)) / 65536e6;
+			freq_step = 10e-6 * (1 << (6 * i));
+			fails += run_test(0, freq_base, freq_step);
+		}
+	}
+
+	set_frequency(0.0);
+
+	if (fails)
+		ksft_exit_fail();
+
+	ksft_exit_pass();
+}