1 /******************************************************************************
2 *
3 * Copyright © International Business Machines Corp., 2006-2008
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
13 * the GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
18 *
19 * NAME
20 * librttest.c
21 *
22 * DESCRIPTION
23 * A set of commonly used convenience functions for writing
24 * threaded realtime test cases.
25 *
26 * USAGE:
27 * To be included in testcases.
28 *
29 * AUTHOR
30 * Darren Hart <dvhltc@us.ibm.com>
31 *
32 * HISTORY
33 * 2006-Apr-26: Initial version by Darren Hart
34 * 2006-May-08: Added atomic_{inc,set,get}, thread struct, debug function,
35 * rt_init, buffered printing -- Vernon Mauery
36 * 2006-May-09: improved command line argument handling
37 * 2007-Jul-12: Added latency tracing functions and I/O helper functions
38 * -- Josh triplett
39 * 2008-Jan-10: Added RR thread support to tests -- Chirag Jog
40 *
41 *****************************************************************************/
42
43 #include <librttest.h>
44 #include <libstats.h>
45
46 #include <stdio.h>
47 #include <stdlib.h>
48 #include <signal.h>
49 #include <time.h>
50 #include <string.h>
51 #include <pthread.h>
52 #include <sched.h>
53 #include <errno.h>
54 #include <unistd.h>
55 #include <getopt.h>
56 #include <sys/prctl.h>
57 #include <sys/stat.h>
58 #include <sys/syscall.h>
59 #include <sys/types.h>
60 #include <sys/mman.h>
61 #include <fcntl.h>
62 #include <math.h>
63
64 static LIST_HEAD(_threads);
65 static atomic_t _thread_count = { -1 };
66
67 pthread_mutex_t _buffer_mutex;
68 char *_print_buffer = NULL;
69 int _print_buffer_offset = 0;
70 int _dbg_lvl = 0;
71 double pass_criteria;
72
73 static int _use_pi = 1;
74
75 /* function implementations */
rt_help(void)76 void rt_help(void)
77 {
78 printf("librt standard options:\n");
79 printf
80 (" -b(0,1) 1:enable buffered output, 0:diable buffered output\n");
81 printf(" -p(0,1) 0:don't use pi mutexes, 1:use pi mutexes\n");
82 printf(" -m use mlockall\n");
83 printf
84 (" -v[0-4] 0:no debug, 1:DBG_ERR, 2:DBG_WARN, 3:DBG_INFO, 4:DBG_DEBUG\n");
85 printf(" -s Enable saving stats data (default disabled)\n");
86 printf(" -c Set pass criteria\n");
87 }
88
89 /* Calibrate the busy work loop */
calibrate_busyloop(void)90 void calibrate_busyloop(void)
91 {
92 volatile int i = CALIBRATE_LOOPS;
93 nsec_t start, end;
94
95 start = rt_gettime();
96 while (--i > 0) {
97 continue;
98 }
99 end = rt_gettime();
100
101 iters_per_us = (CALIBRATE_LOOPS * NS_PER_US) / (end - start);
102 }
103
rt_init_long(const char * options,const struct option * longopts,int (* parse_arg)(int option,char * value),int argc,char * argv[])104 int rt_init_long(const char *options, const struct option *longopts,
105 int (*parse_arg) (int option, char *value), int argc,
106 char *argv[])
107 {
108 const struct option *cur_opt;
109 int use_buffer = 1;
110 char *longopt_vals;
111 size_t i;
112 int c;
113 opterr = 0;
114 int mlock = 0;
115 char *all_options;
116
117 if (asprintf(&all_options, ":b:mp:v:sc:%s", options) == -1) {
118 fprintf(stderr,
119 "Failed to allocate string for option string\n");
120 exit(1);
121 }
122
123 /* Check for duplicate options in optstring */
124 for (i = 0; i < strlen(all_options); i++) {
125 char opt = all_options[i];
126
127 if (opt == ':')
128 continue;
129
130 /* Search ahead */
131 if (strchr(&all_options[i + 1], opt)) {
132 fprintf(stderr,
133 "Programmer error -- argument -%c already used at least twice\n",
134 opt);
135 exit(1);
136 }
137 }
138
139 /* Ensure each long options has a known unique short option in val. */
140 longopt_vals = "";
141 cur_opt = longopts;
142 while (cur_opt && cur_opt->name) {
143 if (cur_opt->flag) {
144 fprintf(stderr, "Programmer error -- argument --%s flag"
145 " is non-null\n", cur_opt->name);
146 exit(1);
147 }
148 if (!strchr(all_options, cur_opt->val)) {
149 fprintf(stderr, "Programmer error -- argument --%s "
150 "shortopt -%c wasn't listed in options (%s)\n",
151 cur_opt->name, cur_opt->val, all_options);
152 exit(1);
153 }
154 if (strchr(longopt_vals, cur_opt->val)) {
155 fprintf(stderr, "Programmer error -- argument --%s "
156 "shortopt -%c is used more than once\n",
157 cur_opt->name, cur_opt->val);
158 exit(1);
159 }
160 if (asprintf(&longopt_vals, "%s%c", longopt_vals, cur_opt->val)
161 < 0) {
162 perror("asprintf");
163 exit(2);
164 }
165 cur_opt++;
166 }
167
168 while ((c = getopt_long(argc, argv, all_options, longopts, NULL)) != -1) {
169 switch (c) {
170 case 'c':
171 pass_criteria = atof(optarg);
172 break;
173 case 'b':
174 use_buffer = atoi(optarg);
175 break;
176 case 'p':
177 _use_pi = atoi(optarg);
178 break;
179 case 'm':
180 mlock = 1;
181 break;
182 case 'v':
183 _dbg_lvl = atoi(optarg);
184 break;
185 case 's':
186 save_stats = 1;
187 break;
188 case ':':
189 if (optopt == '-')
190 fprintf(stderr, "long option missing arg\n");
191 else
192 fprintf(stderr, "option -%c: missing arg\n",
193 optopt);
194 parse_arg('h', optarg); /* Just to display usage */
195 exit(1); /* Just in case. (should normally be done by usage()) */
196 case '?':
197 if (optopt == '-')
198 fprintf(stderr, "unrecognized long option\n");
199 else
200 fprintf(stderr, "option -%c not recognized\n",
201 optopt);
202 parse_arg('h', optarg); /* Just to display usage */
203 exit(1); /* Just in case. (should normally be done by usage()) */
204 default:
205 if (parse_arg && parse_arg(c, optarg))
206 break; /* Application option */
207
208 fprintf(stderr,
209 "Programmer error -- option -%c defined but not handled\n",
210 c);
211 exit(1);
212 }
213 }
214 if (!_use_pi)
215 printf
216 ("Priority Inheritance has been disabled for this run.\n");
217 if (use_buffer)
218 buffer_init();
219 if (mlock) {
220 if (mlockall(MCL_CURRENT | MCL_FUTURE)) {
221 perror("failed to lock memory\n");
222 exit(1);
223 }
224 }
225
226 calibrate_busyloop();
227
228 /*
229 * atexit() order matters here - buffer_print() will be called before
230 * buffer_fini().
231 */
232 atexit(buffer_fini);
233 atexit(buffer_print);
234 return 0;
235 }
236
rt_init(const char * options,int (* parse_arg)(int option,char * value),int argc,char * argv[])237 int rt_init(const char *options, int (*parse_arg) (int option, char *value),
238 int argc, char *argv[])
239 {
240 return rt_init_long(options, NULL, parse_arg, argc, argv);
241 }
242
buffer_init(void)243 void buffer_init(void)
244 {
245 _print_buffer = malloc(PRINT_BUFFER_SIZE);
246 if (!_print_buffer)
247 fprintf(stderr,
248 "insufficient memory for print buffer - printing directly to stderr\n");
249 else
250 memset(_print_buffer, 0, PRINT_BUFFER_SIZE);
251 }
252
buffer_print(void)253 void buffer_print(void)
254 {
255 if (_print_buffer) {
256 fprintf(stderr, "%s", _print_buffer);
257 memset(_print_buffer, 0, PRINT_BUFFER_SIZE);
258 _print_buffer_offset = 0;
259 }
260 }
261
buffer_fini(void)262 void buffer_fini(void)
263 {
264 if (_print_buffer)
265 free(_print_buffer);
266 _print_buffer = NULL;
267 }
268
cleanup(int i)269 void cleanup(int i)
270 {
271 printf("Test terminated with asynchronous signal\n");
272 buffer_print();
273 buffer_fini();
274 if (i)
275 exit(i);
276 }
277
setup()278 void setup()
279 {
280 signal(SIGINT, cleanup);
281 signal(SIGQUIT, cleanup);
282 signal(SIGTERM, cleanup);
283 }
284
create_thread(void * (* func)(void *),void * arg,int prio,int policy)285 int create_thread(void *(*func) (void *), void *arg, int prio, int policy)
286 {
287 struct sched_param param;
288 int id, ret;
289 struct thread *thread;
290
291 id = atomic_inc(&_thread_count);
292
293 thread = malloc(sizeof(struct thread));
294 if (!thread)
295 return -1;
296
297 list_add_tail(&thread->_threads, &_threads);
298 pthread_cond_init(&thread->cond, NULL); // Accept the defaults
299 init_pi_mutex(&thread->mutex);
300 thread->id = id;
301 thread->priority = prio;
302 thread->policy = policy;
303 thread->flags = 0;
304 thread->arg = arg;
305 thread->func = func;
306 param.sched_priority = prio;
307
308 pthread_attr_init(&thread->attr);
309 pthread_attr_setinheritsched(&thread->attr, PTHREAD_EXPLICIT_SCHED);
310 pthread_attr_setschedpolicy(&thread->attr, thread->policy);
311 pthread_attr_setschedparam(&thread->attr, ¶m);
312
313 if ((ret =
314 pthread_create(&thread->pthread, &thread->attr, func,
315 (void *)thread))) {
316 printf("pthread_create failed: %d (%s)\n", ret, strerror(ret));
317 list_del(&thread->_threads);
318 pthread_attr_destroy(&thread->attr);
319 free(thread);
320 return -1;
321 }
322 pthread_attr_destroy(&thread->attr);
323
324 return id;
325 }
326
create_fifo_thread(void * (* func)(void *),void * arg,int prio)327 int create_fifo_thread(void *(*func) (void *), void *arg, int prio)
328 {
329 return create_thread(func, arg, prio, SCHED_FIFO);
330 }
331
create_rr_thread(void * (* func)(void *),void * arg,int prio)332 int create_rr_thread(void *(*func) (void *), void *arg, int prio)
333 {
334 return create_thread(func, arg, prio, SCHED_RR);
335 }
336
create_other_thread(void * (* func)(void *),void * arg)337 int create_other_thread(void *(*func) (void *), void *arg)
338 {
339 return create_thread(func, arg, 0, SCHED_OTHER);
340 }
341
set_thread_priority(pthread_t pthread,int prio)342 int set_thread_priority(pthread_t pthread, int prio)
343 {
344 struct sched_param sched_param;
345 sched_param.sched_priority = prio;
346 int policy;
347
348 policy = (prio > 0) ? SCHED_FIFO : SCHED_OTHER;
349
350 return pthread_setschedparam(pthread, policy, &sched_param);
351 }
352
set_priority(int prio)353 int set_priority(int prio)
354 {
355 struct sched_param sp;
356 int ret = 0;
357
358 sp.sched_priority = prio;
359 if (sched_setscheduler(0, SCHED_FIFO, &sp) != 0) {
360 perror("sched_setscheduler");
361 ret = -1;
362 }
363 return ret;
364 }
365
join_thread(int i)366 void join_thread(int i)
367 {
368 struct thread *p, *t = NULL;
369 list_for_each_entry(p, &_threads, _threads) {
370 if (p->id == i) {
371 t = p;
372 break;
373 }
374 }
375 if (t) {
376 t->flags |= THREAD_QUIT;
377 if (t->pthread)
378 pthread_join(t->pthread, NULL);
379 list_del(&t->_threads);
380 }
381 }
382
all_threads_quit(void)383 void all_threads_quit(void)
384 {
385 struct thread *p;
386 list_for_each_entry(p, &_threads, _threads) {
387 p->flags |= THREAD_QUIT;
388 }
389 }
390
join_threads(void)391 void join_threads(void)
392 {
393 all_threads_quit();
394 struct thread *p, *t;
395 list_for_each_entry_safe(p, t, &_threads, _threads) {
396 if (p->pthread)
397 pthread_join(p->pthread, NULL);
398 list_del(&p->_threads);
399 }
400 }
401
get_thread(int i)402 struct thread *get_thread(int i)
403 {
404 struct thread *p;
405 list_for_each_entry(p, &_threads, _threads) {
406 if (p->id == i) {
407 return p;
408 }
409 }
410 return NULL;
411 }
412
ts_minus(struct timespec * ts_end,struct timespec * ts_start,struct timespec * ts_delta)413 void ts_minus(struct timespec *ts_end, struct timespec *ts_start,
414 struct timespec *ts_delta)
415 {
416 if (ts_end == NULL || ts_start == NULL || ts_delta == NULL) {
417 printf("ERROR in %s: one or more of the timespecs is NULL",
418 __FUNCTION__);
419 return;
420 }
421
422 ts_delta->tv_sec = ts_end->tv_sec - ts_start->tv_sec;
423 ts_delta->tv_nsec = ts_end->tv_nsec - ts_start->tv_nsec;
424 ts_normalize(ts_delta);
425 }
426
ts_plus(struct timespec * ts_a,struct timespec * ts_b,struct timespec * ts_sum)427 void ts_plus(struct timespec *ts_a, struct timespec *ts_b,
428 struct timespec *ts_sum)
429 {
430 if (ts_a == NULL || ts_b == NULL || ts_sum == NULL) {
431 printf("ERROR in %s: one or more of the timespecs is NULL",
432 __FUNCTION__);
433 return;
434 }
435
436 ts_sum->tv_sec = ts_a->tv_sec + ts_b->tv_sec;
437 ts_sum->tv_nsec = ts_a->tv_nsec + ts_b->tv_nsec;
438 ts_normalize(ts_sum);
439 }
440
ts_normalize(struct timespec * ts)441 void ts_normalize(struct timespec *ts)
442 {
443 if (ts == NULL) {
444 /* FIXME: write a real error logging system */
445 printf("ERROR in %s: ts is NULL\n", __FUNCTION__);
446 return;
447 }
448
449 /* get the abs(nsec) < NS_PER_SEC */
450 while (ts->tv_nsec > NS_PER_SEC) {
451 ts->tv_sec++;
452 ts->tv_nsec -= NS_PER_SEC;
453 }
454 while (ts->tv_nsec < -NS_PER_SEC) {
455 ts->tv_sec--;
456 ts->tv_nsec += NS_PER_SEC;
457 }
458
459 /* get the values to the same polarity */
460 if (ts->tv_sec > 0 && ts->tv_nsec < 0) {
461 ts->tv_sec--;
462 ts->tv_nsec += NS_PER_SEC;
463 }
464 if (ts->tv_sec < 0 && ts->tv_nsec > 0) {
465 ts->tv_sec++;
466 ts->tv_nsec -= NS_PER_SEC;
467 }
468 }
469
ts_to_nsec(struct timespec * ts,nsec_t * ns)470 int ts_to_nsec(struct timespec *ts, nsec_t * ns)
471 {
472 struct timespec t;
473 if (ts == NULL) {
474 /* FIXME: write a real error logging system */
475 printf("ERROR in %s: ts is NULL\n", __FUNCTION__);
476 return -1;
477 }
478 t.tv_sec = ts->tv_sec;
479 t.tv_nsec = ts->tv_nsec;
480 ts_normalize(&t);
481
482 if (t.tv_sec <= 0 && t.tv_nsec < 0) {
483 printf("ERROR in %s: ts is negative\n", __FUNCTION__);
484 return -1;
485 }
486
487 *ns = (nsec_t) ts->tv_sec * NS_PER_SEC + ts->tv_nsec;
488 return 0;
489 }
490
nsec_to_ts(nsec_t ns,struct timespec * ts)491 void nsec_to_ts(nsec_t ns, struct timespec *ts)
492 {
493 if (ts == NULL) {
494 /* FIXME: write a real error logging system */
495 printf("ERROR in %s: ts is NULL\n", __FUNCTION__);
496 return;
497 }
498 ts->tv_sec = ns / NS_PER_SEC;
499 ts->tv_nsec = ns % NS_PER_SEC;
500 }
501
502 /* return difference in microseconds */
tsc_minus(unsigned long long tsc_start,unsigned long long tsc_end)503 unsigned long long tsc_minus(unsigned long long tsc_start,
504 unsigned long long tsc_end)
505 {
506 unsigned long long delta;
507 if (tsc_start <= tsc_end)
508 delta = tsc_end - tsc_start;
509 else {
510 delta = ULL_MAX - (tsc_end - tsc_start) + 1;
511 printf("TSC wrapped, delta=%llu\n", delta);
512 }
513 return delta;
514 }
515
rt_nanosleep_until(nsec_t ns)516 void rt_nanosleep_until(nsec_t ns)
517 {
518 struct timespec ts_sleep, ts_rem;
519 int rc;
520 nsec_to_ts(ns, &ts_sleep);
521 rc = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &ts_sleep,
522 &ts_rem);
523 /* FIXME: when should we display the remainder ? */
524 if (rc != 0) {
525 printf("WARNING: rt_nanosleep() returned early by %d s %d ns\n",
526 (int)ts_rem.tv_sec, (int)ts_rem.tv_nsec);
527 }
528 }
529
rt_nanosleep(nsec_t ns)530 void rt_nanosleep(nsec_t ns)
531 {
532 struct timespec ts_sleep, ts_rem;
533 int rc;
534 nsec_to_ts(ns, &ts_sleep);
535 rc = clock_nanosleep(CLOCK_MONOTONIC, 0, &ts_sleep, &ts_rem);
536 /* FIXME: when should we display the remainder ? */
537 if (rc != 0) {
538 printf("WARNING: rt_nanosleep() returned early by %d s %d ns\n",
539 (int)ts_rem.tv_sec, (int)ts_rem.tv_nsec);
540 }
541 }
542
rt_gettime(void)543 nsec_t rt_gettime(void)
544 {
545 struct timespec ts;
546 nsec_t ns;
547 int rc;
548
549 rc = clock_gettime(CLOCK_MONOTONIC, &ts);
550 if (rc != 0) {
551 printf("ERROR in %s: clock_gettime() returned %d\n",
552 __FUNCTION__, rc);
553 perror("clock_gettime() failed");
554 return 0;
555 }
556
557 ts_to_nsec(&ts, &ns);
558 return ns;
559 }
560
busy_work_ms(int ms)561 void *busy_work_ms(int ms)
562 {
563 busy_work_us(ms * US_PER_MS);
564 return NULL;
565 }
566
busy_work_us(int us)567 void *busy_work_us(int us)
568 {
569 volatile int i;
570 nsec_t start, now;
571 int delta; /* time in us */
572
573 i = us * iters_per_us;
574
575 start = rt_gettime();
576 while (--i > 0) {
577 continue;
578 }
579 now = rt_gettime();
580
581 delta = (now - start) / NS_PER_US;
582 /* uncomment to tune to your machine */
583 /* printf("busy_work_us requested: %dus actual: %dus\n", us, delta); */
584 return NULL;
585 }
586
init_pi_mutex(pthread_mutex_t * m)587 void init_pi_mutex(pthread_mutex_t * m)
588 {
589 #if HAS_PRIORITY_INHERIT
590 pthread_mutexattr_t attr;
591 int ret;
592 int protocol;
593
594 if ((ret = pthread_mutexattr_init(&attr)) != 0) {
595 printf("Failed to init mutexattr: %d (%s)\n", ret,
596 strerror(ret));
597 };
598 if (_use_pi
599 && (ret =
600 pthread_mutexattr_setprotocol(&attr,
601 PTHREAD_PRIO_INHERIT)) != 0) {
602 printf("Can't set protocol prio inherit: %d (%s)\n", ret,
603 strerror(ret));
604 }
605 if ((ret = pthread_mutexattr_getprotocol(&attr, &protocol)) != 0) {
606 printf("Can't get mutexattr protocol: %d (%s)\n", ret,
607 strerror(ret));
608 }
609 if ((ret = pthread_mutex_init(m, &attr)) != 0) {
610 printf("Failed to init mutex: %d (%s)\n", ret, strerror(ret));
611 }
612 #endif
613
614 /* FIXME: does any of this need to be destroyed ? */
615 }
616
617 /* Write the entirety of data. Complain if unable to do so. */
write_or_complain(int fd,const void * data,size_t len)618 static void write_or_complain(int fd, const void *data, size_t len)
619 {
620 const char *remaining = data;
621
622 while (len > 0) {
623 ssize_t ret = write(fd, remaining, len);
624 if (ret <= 0) {
625 if (errno != EAGAIN && errno != EINTR) {
626 perror("write");
627 return;
628 }
629 } else {
630 remaining += ret;
631 len -= ret;
632 }
633 }
634 }
635
636 /* Write the given data to the existing file specified by pathname. Complain
637 * if unable to do so. */
write_file(const char * pathname,const void * data,size_t len)638 static void write_file(const char *pathname, const void *data, size_t len)
639 {
640 int fd = open(pathname, O_WRONLY);
641 if (fd < 0) {
642 printf("Failed to open file \"%s\": %d (%s)\n",
643 pathname, errno, strerror(errno));
644 return;
645 }
646
647 write_or_complain(fd, data, len);
648
649 if (close(fd) < 0) {
650 printf("Failed to close file \"%s\": %d (%s)\n",
651 pathname, errno, strerror(errno));
652 }
653 }
654
655 /* Write the given '\0'-terminated string to the existing file specified by
656 * pathname. Complain if unable to do so. */
write_string_to_file(const char * pathname,const char * string)657 static void write_string_to_file(const char *pathname, const char *string)
658 {
659 write_file(pathname, string, strlen(string));
660 }
661
read_and_print(const char * pathname,int output_fd)662 static void read_and_print(const char *pathname, int output_fd)
663 {
664 char data[4096];
665 int fd = open(pathname, O_RDONLY);
666 if (fd < 0) {
667 printf("Failed to open file \"%s\": %d (%s)\n",
668 pathname, errno, strerror(errno));
669 return;
670 }
671
672 while (1) {
673 ssize_t ret = read(fd, data, sizeof(data));
674 if (ret < 0) {
675 if (errno != EAGAIN && errno != EINTR) {
676 printf
677 ("Failed to read from file \"%s\": %d (%s)\n",
678 pathname, errno, strerror(errno));
679 break;
680 }
681 } else if (ret == 0)
682 break;
683 else
684 write_or_complain(output_fd, data, ret);
685 }
686
687 if (close(fd) < 0) {
688 printf("Failed to close file \"%s\": %d (%s)\n",
689 pathname, errno, strerror(errno));
690 }
691 }
692
latency_trace_enable(void)693 void latency_trace_enable(void)
694 {
695 printf("Enabling latency tracer.\n");
696 write_string_to_file("/proc/sys/kernel/trace_use_raw_cycles", "1");
697 write_string_to_file("/proc/sys/kernel/trace_all_cpus", "1");
698 write_string_to_file("/proc/sys/kernel/trace_enabled", "1");
699 write_string_to_file("/proc/sys/kernel/trace_freerunning", "1");
700 write_string_to_file("/proc/sys/kernel/trace_print_on_crash", "0");
701 write_string_to_file("/proc/sys/kernel/trace_user_triggered", "1");
702 write_string_to_file("/proc/sys/kernel/trace_user_trigger_irq", "-1");
703 write_string_to_file("/proc/sys/kernel/trace_verbose", "0");
704 write_string_to_file("/proc/sys/kernel/preempt_thresh", "0");
705 write_string_to_file("/proc/sys/kernel/wakeup_timing", "0");
706 write_string_to_file("/proc/sys/kernel/mcount_enabled", "1");
707 write_string_to_file("/proc/sys/kernel/preempt_max_latency", "0");
708 }
709
710 #ifndef PR_SET_TRACING
711 #define PR_SET_TRACING 0
712 #endif
713
latency_trace_start(void)714 void latency_trace_start(void)
715 {
716 if (prctl(PR_SET_TRACING, 1) < 0)
717 perror("Failed to start tracing");
718 }
719
latency_trace_stop(void)720 void latency_trace_stop(void)
721 {
722 if (prctl(PR_SET_TRACING, 0) < 0)
723 perror("Failed to stop tracing");
724 }
725
latency_trace_print(void)726 void latency_trace_print(void)
727 {
728 read_and_print("/proc/latency_trace", STDOUT_FILENO);
729 }
730