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