lib/timeval.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "timeval.h"
  19 #include <assert.h>
  20 #include <errno.h>
  21 #if HAVE_EXECINFO_H
  22 #include <execinfo.h>
  23 #endif
  24 #include <poll.h>
  25 #include <signal.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <sys/time.h>
  29 #include <sys/resource.h>
  30 #include <unistd.h>
  31 #include "coverage.h"
  32 #include "dummy.h"
  33 #include "dynamic-string.h"
  34 #include "fatal-signal.h"
  35 #include "hash.h"
  36 #include "hmap.h"
  37 #include "signals.h"
  38 #include "unixctl.h"
  39 #include "util.h"
  40 #include "vlog.h"
  41
  42 VLOG_DEFINE_THIS_MODULE(timeval);
  43
  44 /* The clock to use for measuring time intervals.  This is CLOCK_MONOTONIC by
  45  * preference, but on systems that don't have a monotonic clock we fall back
  46  * to CLOCK_REALTIME. */
  47 static clockid_t monotonic_clock;
  48
  49 /* Has a timer tick occurred? Only relevant if CACHE_TIME is true.
  50  *
  51  * We initialize these to true to force time_init() to get called on the first
  52  * call to time_msec() or another function that queries the current time. */
  53 static volatile sig_atomic_t wall_tick = true;
  54 static volatile sig_atomic_t monotonic_tick = true;
  55
  56 /* The current time, as of the last refresh. */
  57 static struct timespec wall_time;
  58 static struct timespec monotonic_time;
  59
  60 /* The monotonic time at which the time module was initialized. */
  61 static long long int boot_time;
  62
  63 /* features for use by unit tests. */
  64 static struct timespec warp_offset; /* Offset added to monotonic_time. */
  65 static bool time_stopped;           /* Disables real-time updates, if true. */
  66
  67 /* Time in milliseconds at which to die with SIGALRM (if not LLONG_MAX). */
  68 static long long int deadline = LLONG_MAX;
  69
  70 struct trace {
  71     void *backtrace[32]; /* Populated by backtrace(). */
  72     size_t n_frames;     /* Number of frames in 'backtrace'. */
  73
  74     /* format_backtraces() helper data. */
  75     struct hmap_node node;
  76     size_t count;
  77 };
  78
  79 #define MAX_TRACES 50
  80 static struct trace traces[MAX_TRACES];
  81 static size_t trace_head = 0;
  82
  83 static void set_up_timer(void);
  84 static void set_up_signal(int flags);
  85 static void sigalrm_handler(int);
  86 static void refresh_wall_if_ticked(void);
  87 static void refresh_monotonic_if_ticked(void);
  88 static void block_sigalrm(sigset_t *);
  89 static void unblock_sigalrm(const sigset_t *);
  90 static void log_poll_interval(long long int last_wakeup);
  91 static struct rusage *get_recent_rusage(void);
  92 static void refresh_rusage(void);
  93 static void timespec_add(struct timespec *sum,
  94                          const struct timespec *a, const struct timespec *b);
  95 static unixctl_cb_func backtrace_cb;
  96
  97 #ifndef HAVE_EXECINFO_H
  98 #define HAVE_EXECINFO_H 0
  99
 100 static int
 101 backtrace(void **buffer OVS_UNUSED, int size OVS_UNUSED)
 102 {
 103     NOT_REACHED();
 104 }
 105
 106 static char **
 107 backtrace_symbols(void *const *buffer OVS_UNUSED, int size OVS_UNUSED)
 108 {
 109     NOT_REACHED();
 110 }
 111 #endif
 112
 113 /* Initializes the timetracking module, if not already initialized. */
 114 static void
 115 time_init(void)
 116 {
 117     static bool inited;
 118
 119     if (inited) {
 120         return;
 121     }
 122     inited = true;
 123
 124     /* The implementation of backtrace() in glibc does some one time
 125      * initialization which is not signal safe.  This can cause deadlocks if
 126      * run from the signal handler.  As a workaround, force the initialization
 127      * to happen here. */
 128     if (HAVE_EXECINFO_H) {
 129         void *bt[1];
 130
 131         backtrace(bt, ARRAY_SIZE(bt));
 132     }
 133
 134     memset(traces, 0, sizeof traces);
 135
 136     if (HAVE_EXECINFO_H && CACHE_TIME) {
 137         unixctl_command_register("backtrace", "", 0, 0, backtrace_cb, NULL);
 138     }
 139
 140     coverage_init();
 141
 142     if (!clock_gettime(CLOCK_MONOTONIC, &monotonic_time)) {
 143         monotonic_clock = CLOCK_MONOTONIC;
 144     } else {
 145         monotonic_clock = CLOCK_REALTIME;
 146         VLOG_DBG("monotonic timer not available");
 147     }
 148
 149     set_up_signal(SA_RESTART);
 150     set_up_timer();
 151
 152     boot_time = time_msec();
 153 }
 154
 155 static void
 156 set_up_signal(int flags)
 157 {
 158     struct sigaction sa;
 159
 160     memset(&sa, 0, sizeof sa);
 161     sa.sa_handler = sigalrm_handler;
 162     sigemptyset(&sa.sa_mask);
 163     sa.sa_flags = flags;
 164     xsigaction(SIGALRM, &sa, NULL);
 165 }
 166
 167 /* Remove SA_RESTART from the flags for SIGALRM, so that any system call that
 168  * is interrupted by the periodic timer interrupt will return EINTR instead of
 169  * continuing after the signal handler returns.
 170  *
 171  * time_disable_restart() and time_enable_restart() may be usefully wrapped
 172  * around function calls that might otherwise block forever unless interrupted
 173  * by a signal, e.g.:
 174  *
 175  *   time_disable_restart();
 176  *   fcntl(fd, F_SETLKW, &lock);
 177  *   time_enable_restart();
 178  */
 179 void
 180 time_disable_restart(void)
 181 {
 182     time_init();
 183     set_up_signal(0);
 184 }
 185
 186 /* Add SA_RESTART to the flags for SIGALRM, so that any system call that
 187  * is interrupted by the periodic timer interrupt will continue after the
 188  * signal handler returns instead of returning EINTR. */
 189 void
 190 time_enable_restart(void)
 191 {
 192     time_init();
 193     set_up_signal(SA_RESTART);
 194 }
 195
 196 static void
 197 set_up_timer(void)
 198 {
 199     static timer_t timer_id;    /* "static" to avoid apparent memory leak. */
 200     struct itimerspec itimer;
 201
 202     if (!CACHE_TIME) {
 203         return;
 204     }
 205
 206     if (timer_create(monotonic_clock, NULL, &timer_id)) {
 207         VLOG_FATAL("timer_create failed (%s)", strerror(errno));
 208     }
 209
 210     itimer.it_interval.tv_sec = 0;
 211     itimer.it_interval.tv_nsec = TIME_UPDATE_INTERVAL * 1000 * 1000;
 212     itimer.it_value = itimer.it_interval;
 213
 214     if (timer_settime(timer_id, 0, &itimer, NULL)) {
 215         VLOG_FATAL("timer_settime failed (%s)", strerror(errno));
 216     }
 217 }
 218
 219 /* Set up the interval timer, to ensure that time advances even without calling
 220  * time_refresh().
 221  *
 222  * A child created with fork() does not inherit the parent's interval timer, so
 223  * this function needs to be called from the child after fork(). */
 224 void
 225 time_postfork(void)
 226 {
 227     time_init();
 228     set_up_timer();
 229 }
 230
 231 static void
 232 refresh_wall(void)
 233 {
 234     time_init();
 235     clock_gettime(CLOCK_REALTIME, &wall_time);
 236     wall_tick = false;
 237 }
 238
 239 static void
 240 refresh_monotonic(void)
 241 {
 242     time_init();
 243
 244     if (!time_stopped) {
 245         if (monotonic_clock == CLOCK_MONOTONIC) {
 246             clock_gettime(monotonic_clock, &monotonic_time);
 247         } else {
 248             refresh_wall_if_ticked();
 249             monotonic_time = wall_time;
 250         }
 251         timespec_add(&monotonic_time, &monotonic_time, &warp_offset);
 252
 253         monotonic_tick = false;
 254     }
 255 }
 256
 257 /* Forces a refresh of the current time from the kernel.  It is not usually
 258  * necessary to call this function, since the time will be refreshed
 259  * automatically at least every TIME_UPDATE_INTERVAL milliseconds.  If
 260  * CACHE_TIME is false, we will always refresh the current time so this
 261  * function has no effect. */
 262 void
 263 time_refresh(void)
 264 {
 265     wall_tick = monotonic_tick = true;
 266 }
 267
 268 /* Returns a monotonic timer, in seconds. */
 269 time_t
 270 time_now(void)
 271 {
 272     refresh_monotonic_if_ticked();
 273     return monotonic_time.tv_sec;
 274 }
 275
 276 /* Returns the current time, in seconds. */
 277 time_t
 278 time_wall(void)
 279 {
 280     refresh_wall_if_ticked();
 281     return wall_time.tv_sec;
 282 }
 283
 284 /* Returns a monotonic timer, in ms (within TIME_UPDATE_INTERVAL ms). */
 285 long long int
 286 time_msec(void)
 287 {
 288     refresh_monotonic_if_ticked();
 289     return timespec_to_msec(&monotonic_time);
 290 }
 291
 292 /* Returns the current time, in ms (within TIME_UPDATE_INTERVAL ms). */
 293 long long int
 294 time_wall_msec(void)
 295 {
 296     refresh_wall_if_ticked();
 297     return timespec_to_msec(&wall_time);
 298 }
 299
 300 /* Stores a monotonic timer, accurate within TIME_UPDATE_INTERVAL ms, into
 301  * '*ts'. */
 302 void
 303 time_timespec(struct timespec *ts)
 304 {
 305     refresh_monotonic_if_ticked();
 306     *ts = monotonic_time;
 307 }
 308
 309 /* Stores the current time, accurate within TIME_UPDATE_INTERVAL ms, into
 310  * '*ts'. */
 311 void
 312 time_wall_timespec(struct timespec *ts)
 313 {
 314     refresh_wall_if_ticked();
 315     *ts = wall_time;
 316 }
 317
 318 /* Configures the program to die with SIGALRM 'secs' seconds from now, if
 319  * 'secs' is nonzero, or disables the feature if 'secs' is zero. */
 320 void
 321 time_alarm(unsigned int secs)
 322 {
 323     long long int now;
 324     long long int msecs;
 325
 326     sigset_t oldsigs;
 327
 328     time_init();
 329     time_refresh();
 330
 331     now = time_msec();
 332     msecs = secs * 1000;
 333
 334     block_sigalrm(&oldsigs);
 335     deadline = now < LLONG_MAX - msecs ? now + msecs : LLONG_MAX;
 336     unblock_sigalrm(&oldsigs);
 337 }
 338
 339 /* Like poll(), except:
 340  *
 341  *      - The timeout is specified as an absolute time, as defined by
 342  *        time_msec(), instead of a duration.
 343  *
 344  *      - On error, returns a negative error code (instead of setting errno).
 345  *
 346  *      - If interrupted by a signal, retries automatically until the original
 347  *        timeout is reached.  (Because of this property, this function will
 348  *        never return -EINTR.)
 349  *
 350  *      - As a side effect, refreshes the current time (like time_refresh()).
 351  *
 352  * Stores the number of milliseconds elapsed during poll in '*elapsed'. */
 353 int
 354 time_poll(struct pollfd *pollfds, int n_pollfds, long long int timeout_when,
 355           int *elapsed)
 356 {
 357     static long long int last_wakeup = 0;
 358     long long int start;
 359     sigset_t oldsigs;
 360     bool blocked;
 361     int retval;
 362
 363     time_refresh();
 364     if (last_wakeup) {
 365         log_poll_interval(last_wakeup);
 366     }
 367     coverage_clear();
 368     start = time_msec();
 369     blocked = false;
 370
 371     timeout_when = MIN(timeout_when, deadline);
 372
 373     for (;;) {
 374         long long int now = time_msec();
 375         int time_left;
 376
 377         if (now >= timeout_when) {
 378             time_left = 0;
 379         } else if ((unsigned long long int) timeout_when - now > INT_MAX) {
 380             time_left = INT_MAX;
 381         } else {
 382             time_left = timeout_when - now;
 383         }
 384
 385         retval = poll(pollfds, n_pollfds, time_left);
 386         if (retval < 0) {
 387             retval = -errno;
 388         }
 389
 390         time_refresh();
 391         if (deadline <= time_msec()) {
 392             fatal_signal_handler(SIGALRM);
 393             if (retval < 0) {
 394                 retval = 0;
 395             }
 396             break;
 397         }
 398
 399         if (retval != -EINTR) {
 400             break;
 401         }
 402
 403         if (!blocked && CACHE_TIME) {
 404             block_sigalrm(&oldsigs);
 405             blocked = true;
 406         }
 407     }
 408     if (blocked) {
 409         unblock_sigalrm(&oldsigs);
 410     }
 411     last_wakeup = time_msec();
 412     refresh_rusage();
 413     *elapsed = last_wakeup - start;
 414     return retval;
 415 }
 416
 417 static void
 418 sigalrm_handler(int sig_nr OVS_UNUSED)
 419 {
 420     wall_tick = true;
 421     monotonic_tick = true;
 422
 423     if (HAVE_EXECINFO_H && CACHE_TIME) {
 424         struct trace *trace = &traces[trace_head];
 425
 426         trace->n_frames = backtrace(trace->backtrace,
 427                                     ARRAY_SIZE(trace->backtrace));
 428         trace_head = (trace_head + 1) % MAX_TRACES;
 429     }
 430 }
 431
 432 static void
 433 refresh_wall_if_ticked(void)
 434 {
 435     if (!CACHE_TIME || wall_tick) {
 436         refresh_wall();
 437     }
 438 }
 439
 440 static void
 441 refresh_monotonic_if_ticked(void)
 442 {
 443     if (!CACHE_TIME || monotonic_tick) {
 444         refresh_monotonic();
 445     }
 446 }
 447
 448 static void
 449 block_sigalrm(sigset_t *oldsigs)
 450 {
 451     sigset_t sigalrm;
 452     sigemptyset(&sigalrm);
 453     sigaddset(&sigalrm, SIGALRM);
 454     xsigprocmask(SIG_BLOCK, &sigalrm, oldsigs);
 455 }
 456
 457 static void
 458 unblock_sigalrm(const sigset_t *oldsigs)
 459 {
 460     xsigprocmask(SIG_SETMASK, oldsigs, NULL);
 461 }
 462
 463 long long int
 464 timespec_to_msec(const struct timespec *ts)
 465 {
 466     return (long long int) ts->tv_sec * 1000 + ts->tv_nsec / (1000 * 1000);
 467 }
 468
 469 long long int
 470 timeval_to_msec(const struct timeval *tv)
 471 {
 472     return (long long int) tv->tv_sec * 1000 + tv->tv_usec / 1000;
 473 }
 474
 475 /* Returns the monotonic time at which the "time" module was initialized, in
 476  * milliseconds(). */
 477 long long int
 478 time_boot_msec(void)
 479 {
 480     time_init();
 481     return boot_time;
 482 }
 483
 484 void
 485 xgettimeofday(struct timeval *tv)
 486 {
 487     if (gettimeofday(tv, NULL) == -1) {
 488         VLOG_FATAL("gettimeofday failed (%s)", strerror(errno));
 489     }
 490 }
 491
 492 static long long int
 493 timeval_diff_msec(const struct timeval *a, const struct timeval *b)
 494 {
 495     return timeval_to_msec(a) - timeval_to_msec(b);
 496 }
 497
 498 static void
 499 timespec_add(struct timespec *sum,
 500              const struct timespec *a,
 501              const struct timespec *b)
 502 {
 503     struct timespec tmp;
 504
 505     tmp.tv_sec = a->tv_sec + b->tv_sec;
 506     tmp.tv_nsec = a->tv_nsec + b->tv_nsec;
 507     if (tmp.tv_nsec >= 1000 * 1000 * 1000) {
 508         tmp.tv_nsec -= 1000 * 1000 * 1000;
 509         tmp.tv_sec++;
 510     }
 511
 512     *sum = tmp;
 513 }
 514
 515 static void
 516 log_poll_interval(long long int last_wakeup)
 517 {
 518     long long int interval = time_msec() - last_wakeup;
 519
 520     if (interval >= 1000) {
 521         const struct rusage *last_rusage = get_recent_rusage();
 522         struct rusage rusage;
 523
 524         getrusage(RUSAGE_SELF, &rusage);
 525         VLOG_WARN("Unreasonably long %lldms poll interval"
 526                   " (%lldms user, %lldms system)",
 527                   interval,
 528                   timeval_diff_msec(&rusage.ru_utime,
 529                                     &last_rusage->ru_utime),
 530                   timeval_diff_msec(&rusage.ru_stime,
 531                                     &last_rusage->ru_stime));
 532         if (rusage.ru_minflt > last_rusage->ru_minflt
 533             || rusage.ru_majflt > last_rusage->ru_majflt) {
 534             VLOG_WARN("faults: %ld minor, %ld major",
 535                       rusage.ru_minflt - last_rusage->ru_minflt,
 536                       rusage.ru_majflt - last_rusage->ru_majflt);
 537         }
 538         if (rusage.ru_inblock > last_rusage->ru_inblock
 539             || rusage.ru_oublock > last_rusage->ru_oublock) {
 540             VLOG_WARN("disk: %ld reads, %ld writes",
 541                       rusage.ru_inblock - last_rusage->ru_inblock,
 542                       rusage.ru_oublock - last_rusage->ru_oublock);
 543         }
 544         if (rusage.ru_nvcsw > last_rusage->ru_nvcsw
 545             || rusage.ru_nivcsw > last_rusage->ru_nivcsw) {
 546             VLOG_WARN("context switches: %ld voluntary, %ld involuntary",
 547                       rusage.ru_nvcsw - last_rusage->ru_nvcsw,
 548                       rusage.ru_nivcsw - last_rusage->ru_nivcsw);
 549         }
 550         coverage_log();
 551     }
 552 }
 553 \f
 554 /* CPU usage tracking. */
 555
 556 struct cpu_usage {
 557     long long int when;         /* Time that this sample was taken. */
 558     unsigned long long int cpu; /* Total user+system CPU usage when sampled. */
 559 };
 560
 561 static struct rusage recent_rusage;
 562 static struct cpu_usage older = { LLONG_MIN, 0 };
 563 static struct cpu_usage newer = { LLONG_MIN, 0 };
 564 static int cpu_usage = -1;
 565
 566 static struct rusage *
 567 get_recent_rusage(void)
 568 {
 569     return &recent_rusage;
 570 }
 571
 572 static void
 573 refresh_rusage(void)
 574 {
 575     long long int now;
 576
 577     now = time_msec();
 578     getrusage(RUSAGE_SELF, &recent_rusage);
 579
 580     if (now >= newer.when + 3 * 1000) {
 581         older = newer;
 582         newer.when = now;
 583         newer.cpu = (timeval_to_msec(&recent_rusage.ru_utime) +
 584                      timeval_to_msec(&recent_rusage.ru_stime));
 585
 586         if (older.when != LLONG_MIN && newer.cpu > older.cpu) {
 587             unsigned int dividend = newer.cpu - older.cpu;
 588             unsigned int divisor = (newer.when - older.when) / 100;
 589             cpu_usage = divisor > 0 ? dividend / divisor : -1;
 590         } else {
 591             cpu_usage = -1;
 592         }
 593     }
 594 }
 595
 596 /* Returns an estimate of this process's CPU usage, as a percentage, over the
 597  * past few seconds of wall-clock time.  Returns -1 if no estimate is available
 598  * (which will happen if the process has not been running long enough to have
 599  * an estimate, and can happen for other reasons as well). */
 600 int
 601 get_cpu_usage(void)
 602 {
 603     return cpu_usage;
 604 }
 605
 606 static uint32_t
 607 hash_trace(struct trace *trace)
 608 {
 609     return hash_bytes(trace->backtrace,
 610                       trace->n_frames * sizeof *trace->backtrace, 0);
 611 }
 612
 613 static struct trace *
 614 trace_map_lookup(struct hmap *trace_map, struct trace *key)
 615 {
 616     struct trace *value;
 617
 618     HMAP_FOR_EACH_WITH_HASH (value, node, hash_trace(key), trace_map) {
 619         if (key->n_frames == value->n_frames
 620             && !memcmp(key->backtrace, value->backtrace,
 621                        key->n_frames * sizeof *key->backtrace)) {
 622             return value;
 623         }
 624     }
 625     return NULL;
 626 }
 627
 628 /*  Appends a string to 'ds' representing backtraces recorded at regular
 629  *  intervals in the recent past.  This information can be used to get a sense
 630  *  of what the process has been spending the majority of time doing.  Will
 631  *  ommit any backtraces which have not occurred at least 'min_count' times. */
 632 void
 633 format_backtraces(struct ds *ds, size_t min_count)
 634 {
 635     time_init();
 636
 637     if (HAVE_EXECINFO_H && CACHE_TIME) {
 638         struct hmap trace_map = HMAP_INITIALIZER(&trace_map);
 639         struct trace *trace, *next;
 640         sigset_t oldsigs;
 641         size_t i;
 642
 643         block_sigalrm(&oldsigs);
 644
 645         for (i = 0; i < MAX_TRACES; i++) {
 646             struct trace *trace = &traces[i];
 647             struct trace *map_trace;
 648
 649             if (!trace->n_frames) {
 650                 continue;
 651             }
 652
 653             map_trace = trace_map_lookup(&trace_map, trace);
 654             if (map_trace) {
 655                 map_trace->count++;
 656             } else {
 657                 hmap_insert(&trace_map, &trace->node, hash_trace(trace));
 658                 trace->count = 1;
 659             }
 660         }
 661
 662         HMAP_FOR_EACH_SAFE (trace, next, node, &trace_map) {
 663             char **frame_strs;
 664             size_t j;
 665
 666             hmap_remove(&trace_map, &trace->node);
 667
 668             if (trace->count < min_count) {
 669                 continue;
 670             }
 671
 672             frame_strs = backtrace_symbols(trace->backtrace, trace->n_frames);
 673
 674             ds_put_format(ds, "Count %zu\n", trace->count);
 675             for (j = 0; j < trace->n_frames; j++) {
 676                 ds_put_format(ds, "%s\n", frame_strs[j]);
 677             }
 678             ds_put_cstr(ds, "\n");
 679
 680             free(frame_strs);
 681         }
 682         hmap_destroy(&trace_map);
 683
 684         ds_chomp(ds, '\n');
 685         unblock_sigalrm(&oldsigs);
 686     }
 687 }
 688 \f
 689 /* Unixctl interface. */
 690
 691 /* "time/stop" stops the monotonic time returned by e.g. time_msec() from
 692  * advancing, except due to later calls to "time/warp". */
 693 static void
 694 timeval_stop_cb(struct unixctl_conn *conn,
 695                  int argc OVS_UNUSED, const char *argv[] OVS_UNUSED,
 696                  void *aux OVS_UNUSED)
 697 {
 698     time_stopped = true;
 699     unixctl_command_reply(conn, NULL);
 700 }
 701
 702 /* "time/warp MSECS" advances the current monotonic time by the specified
 703  * number of milliseconds.  Unless "time/stop" has also been executed, the
 704  * monotonic clock continues to tick forward at the normal rate afterward.
 705  *
 706  * Does not affect wall clock readings. */
 707 static void
 708 timeval_warp_cb(struct unixctl_conn *conn,
 709                 int argc OVS_UNUSED, const char *argv[], void *aux OVS_UNUSED)
 710 {
 711     struct timespec ts;
 712     int msecs;
 713
 714     msecs = atoi(argv[1]);
 715     if (msecs <= 0) {
 716         unixctl_command_reply_error(conn, "invalid MSECS");
 717         return;
 718     }
 719
 720     ts.tv_sec = msecs / 1000;
 721     ts.tv_nsec = (msecs % 1000) * 1000 * 1000;
 722     timespec_add(&warp_offset, &warp_offset, &ts);
 723     timespec_add(&monotonic_time, &monotonic_time, &ts);
 724     unixctl_command_reply(conn, "warped");
 725 }
 726
 727 static void
 728 backtrace_cb(struct unixctl_conn *conn,
 729              int argc OVS_UNUSED, const char *argv[] OVS_UNUSED,
 730              void *aux OVS_UNUSED)
 731 {
 732     struct ds ds = DS_EMPTY_INITIALIZER;
 733
 734     assert(HAVE_EXECINFO_H && CACHE_TIME);
 735     format_backtraces(&ds, 0);
 736     unixctl_command_reply(conn, ds_cstr(&ds));
 737     ds_destroy(&ds);
 738 }
 739
 740 void
 741 timeval_dummy_register(void)
 742 {
 743     unixctl_command_register("time/stop", "", 0, 0, timeval_stop_cb, NULL);
 744     unixctl_command_register("time/warp", "MSECS", 1, 1,
 745                              timeval_warp_cb, NULL);
 746 }