selftests/timers: Add threaded time inconsistency test from timetest suite

Add the threaded time inconsistency test from the timetest suite.
This checks for time inconsistencies between cpus, usually associated
with clock skew as sometimes found w/ TSCs.

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

···
 CFLAGS += -O3 -Wl,-no-as-needed -Wall $(BUILD_FLAGS)
 LDFLAGS += -lrt -lpthread
 bins = posix_timers nanosleep inconsistency-check nsleep-lat raw_skew \
-	set-timer-lat
+	set-timer-lat threadtest
 
 all: ${bins}
 
···
 	./set-timer-lat
 	./inconsistency-check
 	./raw_skew
-
+	./threadtest -t 30 -n 8
 clean:
 	rm -f ${bins}

tools/testing/selftests/timers/threadtest.c

···
+/* threadtest.c
+ *		by: john stultz ([e-mail])
+ *		(C) Copyright IBM 2004, 2005, 2006, 2012
+ *		Licensed under the GPLv2
+ *
+ *  To build:
+ *	$ gcc threadtest.c -o threadtest -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 <pthread.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
+
+
+/* serializes shared list access */
+pthread_mutex_t list_lock = PTHREAD_MUTEX_INITIALIZER;
+/* serializes console output */
+pthread_mutex_t print_lock = PTHREAD_MUTEX_INITIALIZER;
+
+
+#define MAX_THREADS 128
+#define LISTSIZE 128
+
+int done = 0;
+
+struct timespec global_list[LISTSIZE];
+int listcount = 0;
+
+
+void checklist(struct timespec *list, int size)
+{
+	int i, j;
+	struct timespec *a, *b;
+
+	/* scan the list */
+	for (i = 0; i < size-1; i++) {
+		a = &list[i];
+		b = &list[i+1];
+
+		/* look for any time inconsistencies */
+		if ((b->tv_sec <= a->tv_sec) &&
+			(b->tv_nsec < a->tv_nsec)) {
+
+			/* flag other threads */
+			done = 1;
+
+			/*serialize printing to avoid junky output*/
+			pthread_mutex_lock(&print_lock);
+
+			/* dump the list */
+			printf("\n");
+			for (j = 0; j < size; j++) {
+				if (j == i)
+					printf("---------------\n");
+				printf("%lu:%lu\n", list[j].tv_sec, list[j].tv_nsec);
+				if (j == i+1)
+					printf("---------------\n");
+			}
+			printf("[FAILED]\n");
+
+			pthread_mutex_unlock(&print_lock);
+		}
+	}
+}
+
+/* The shared thread shares a global list
+ * that each thread fills while holding the lock.
+ * This stresses clock syncronization across cpus.
+ */
+void *shared_thread(void *arg)
+{
+	while (!done) {
+		/* protect the list */
+		pthread_mutex_lock(&list_lock);
+
+		/* see if we're ready to check the list */
+		if (listcount >= LISTSIZE) {
+			checklist(global_list, LISTSIZE);
+			listcount = 0;
+		}
+		clock_gettime(CLOCK_MONOTONIC, &global_list[listcount++]);
+
+		pthread_mutex_unlock(&list_lock);
+	}
+	return NULL;
+}
+
+
+/* Each independent thread fills in its own
+ * list. This stresses clock_gettime() lock contention.
+ */
+void *independent_thread(void *arg)
+{
+	struct timespec my_list[LISTSIZE];
+	int count;
+
+	while (!done) {
+		/* fill the list */
+		for (count = 0; count < LISTSIZE; count++)
+			clock_gettime(CLOCK_MONOTONIC, &my_list[count]);
+		checklist(my_list, LISTSIZE);
+	}
+	return NULL;
+}
+
+
+int main(int argc, char **argv)
+{
+	int thread_count = 1, i;
+	time_t start, now, runtime = 60;
+	char buf[255];
+	pthread_t pth[MAX_THREADS];
+	int opt;
+	void *tret;
+	int ret = 0;
+	void *(*thread)(void *) = shared_thread;
+
+
+	/* Process arguments */
+	while ((opt = getopt(argc, argv, "t:n:i")) != -1) {
+		switch (opt) {
+		case 't':
+			runtime = atoi(optarg);
+			break;
+		case 'n':
+			thread_count = atoi(optarg);
+			break;
+		case 'i':
+			thread = independent_thread;
+			printf("using independent threads\n");
+			break;
+		default:
+			printf("Usage: %s [-t <secs>] [-n <numthreads>] [-i]\n", argv[0]);
+			printf("	-t: time to run\n");
+			printf("	-n: number of threads\n");
+			printf("	-i: use independent threads\n");
+			return -1;
+		}
+	}
+
+	if (thread_count > MAX_THREADS)
+		thread_count = MAX_THREADS;
+
+
+	setbuf(stdout, NULL);
+
+	start = time(0);
+	strftime(buf, 255, "%a, %d %b %Y %T %z", localtime(&start));
+	printf("%s\n", buf);
+	printf("Testing consistency with %i threads for %ld seconds: ", thread_count, runtime);
+
+	/* spawn */
+	for (i = 0; i < thread_count; i++)
+		pthread_create(&pth[i], 0, thread, 0);
+
+	while (time(&now) < start + runtime) {
+		sleep(1);
+		if (done) {
+			ret = 1;
+			strftime(buf, 255, "%a, %d %b %Y %T %z", localtime(&now));
+			printf("%s\n", buf);
+			goto out;
+		}
+	}
+	printf("[OK]\n");
+	done = 1;
+
+out:
+	/* wait */
+	for (i = 0; i < thread_count; i++)
+		pthread_join(pth[i], &tret);
+
+	/* die */
+	if (ret)
+		ksft_exit_fail();
+	return ksft_exit_pass();
+}