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