selftests/timers: Add nsleep-lat test from timetest suite

Adds my nanosleep latency test from the timetest suite.
This checks to make sure we don't see "unreasonable"
latencies (> 40ms) when calling nanosleep.

Cc: Shuah Khan <[e-mail]>
Cc: Prarit Bhargava <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Richard Cochran <[e-mail]>
Signed-off-by: John Stultz <[e-mail]>
Tested-by: Prarit Bhargava <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/timers/Makefile

···
 BUILD_FLAGS = -DKTEST
 CFLAGS += -O3 -Wl,-no-as-needed -Wall $(BUILD_FLAGS)
 LDFLAGS += -lrt -lpthread
-bins = posix_timers nanosleep inconsistency-check
+bins = posix_timers nanosleep inconsistency-check nsleep-lat
 
 all: ${bins}
 
 run_tests: all
 	./posix_timers
 	./nanosleep
+	./nsleep-lat
 	./inconsistency-check
 clean:
 	rm -f ${bins}

tools/testing/selftests/timers/nsleep-lat.c

···
+/* Measure nanosleep timer latency
+ *              by: john stultz ([e-mail])
+ *		(C) Copyright Linaro 2013
+ *              Licensed under the GPLv2
+ *
+ *  To build:
+ *	$ gcc nsleep-lat.c -o nsleep-lat -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 <stdlib.h>
+#include <time.h>
+#include <sys/time.h>
+#include <sys/timex.h>
+#include <string.h>
+#include <signal.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 NSEC_PER_SEC 1000000000ULL
+
+#define UNRESONABLE_LATENCY 40000000 /* 40ms in nanosecs */
+
+
+#define CLOCK_REALTIME			0
+#define CLOCK_MONOTONIC			1
+#define CLOCK_PROCESS_CPUTIME_ID	2
+#define CLOCK_THREAD_CPUTIME_ID		3
+#define CLOCK_MONOTONIC_RAW		4
+#define CLOCK_REALTIME_COARSE		5
+#define CLOCK_MONOTONIC_COARSE		6
+#define CLOCK_BOOTTIME			7
+#define CLOCK_REALTIME_ALARM		8
+#define CLOCK_BOOTTIME_ALARM		9
+#define CLOCK_HWSPECIFIC		10
+#define CLOCK_TAI			11
+#define NR_CLOCKIDS			12
+
+#define UNSUPPORTED 0xf00f
+
+char *clockstring(int clockid)
+{
+	switch (clockid) {
+	case CLOCK_REALTIME:
+		return "CLOCK_REALTIME";
+	case CLOCK_MONOTONIC:
+		return "CLOCK_MONOTONIC";
+	case CLOCK_PROCESS_CPUTIME_ID:
+		return "CLOCK_PROCESS_CPUTIME_ID";
+	case CLOCK_THREAD_CPUTIME_ID:
+		return "CLOCK_THREAD_CPUTIME_ID";
+	case CLOCK_MONOTONIC_RAW:
+		return "CLOCK_MONOTONIC_RAW";
+	case CLOCK_REALTIME_COARSE:
+		return "CLOCK_REALTIME_COARSE";
+	case CLOCK_MONOTONIC_COARSE:
+		return "CLOCK_MONOTONIC_COARSE";
+	case CLOCK_BOOTTIME:
+		return "CLOCK_BOOTTIME";
+	case CLOCK_REALTIME_ALARM:
+		return "CLOCK_REALTIME_ALARM";
+	case CLOCK_BOOTTIME_ALARM:
+		return "CLOCK_BOOTTIME_ALARM";
+	case CLOCK_TAI:
+		return "CLOCK_TAI";
+	};
+	return "UNKNOWN_CLOCKID";
+}
+
+struct timespec timespec_add(struct timespec ts, unsigned long long ns)
+{
+	ts.tv_nsec += ns;
+	while (ts.tv_nsec >= NSEC_PER_SEC) {
+		ts.tv_nsec -= NSEC_PER_SEC;
+		ts.tv_sec++;
+	}
+	return ts;
+}
+
+
+long long timespec_sub(struct timespec a, struct timespec b)
+{
+	long long ret = NSEC_PER_SEC * b.tv_sec + b.tv_nsec;
+
+	ret -= NSEC_PER_SEC * a.tv_sec + a.tv_nsec;
+	return ret;
+}
+
+int nanosleep_lat_test(int clockid, long long ns)
+{
+	struct timespec start, end, target;
+	long long latency = 0;
+	int i, count;
+
+	target.tv_sec = ns/NSEC_PER_SEC;
+	target.tv_nsec = ns%NSEC_PER_SEC;
+
+	if (clock_gettime(clockid, &start))
+		return UNSUPPORTED;
+	if (clock_nanosleep(clockid, 0, &target, NULL))
+		return UNSUPPORTED;
+
+	count = 10;
+
+	/* First check relative latency */
+	clock_gettime(clockid, &start);
+	for (i = 0; i < count; i++)
+		clock_nanosleep(clockid, 0, &target, NULL);
+	clock_gettime(clockid, &end);
+
+	if (((timespec_sub(start, end)/count)-ns) > UNRESONABLE_LATENCY) {
+		printf("Large rel latency: %lld ns :", (timespec_sub(start, end)/count)-ns);
+		return -1;
+	}
+
+	/* Next check absolute latency */
+	for (i = 0; i < count; i++) {
+		clock_gettime(clockid, &start);
+		target = timespec_add(start, ns);
+		clock_nanosleep(clockid, TIMER_ABSTIME, &target, NULL);
+		clock_gettime(clockid, &end);
+		latency += timespec_sub(target, end);
+	}
+
+	if (latency/count > UNRESONABLE_LATENCY) {
+		printf("Large abs latency: %lld ns :", latency/count);
+		return -1;
+	}
+
+	return 0;
+}
+
+
+
+int main(int argc, char **argv)
+{
+	long long length;
+	int clockid, ret;
+
+	for (clockid = CLOCK_REALTIME; clockid < NR_CLOCKIDS; clockid++) {
+
+		/* Skip cputime clockids since nanosleep won't increment cputime */
+		if (clockid == CLOCK_PROCESS_CPUTIME_ID ||
+				clockid == CLOCK_THREAD_CPUTIME_ID ||
+				clockid == CLOCK_HWSPECIFIC)
+			continue;
+
+		printf("nsleep latency %-26s ", clockstring(clockid));
+
+		length = 10;
+		while (length <= (NSEC_PER_SEC * 10)) {
+			ret = nanosleep_lat_test(clockid, length);
+			if (ret)
+				break;
+			length *= 100;
+
+		}
+
+		if (ret == UNSUPPORTED) {
+			printf("[UNSUPPORTED]\n");
+			continue;
+		}
+		if (ret < 0) {
+			printf("[FAILED]\n");
+			return ksft_exit_fail();
+		}
+		printf("[OK]\n");
+	}
+	return ksft_exit_pass();
+}