The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_timeout.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      From: @(#)kern_clock.c  8.5 (Berkeley) 1/21/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD$");
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/callout.h>
   43 #include <sys/condvar.h>
   44 #include <sys/kernel.h>
   45 #include <sys/ktr.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 #include <sys/sysctl.h>
   49 
   50 static int avg_depth;
   51 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
   52     "Average number of items examined per softclock call. Units = 1/1000");
   53 static int avg_gcalls;
   54 SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
   55     "Average number of Giant callouts made per softclock call. Units = 1/1000");
   56 static int avg_mpcalls;
   57 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
   58     "Average number of MP callouts made per softclock call. Units = 1/1000");
   59 /*
   60  * TODO:
   61  *      allocate more timeout table slots when table overflows.
   62  */
   63 
   64 /* Exported to machdep.c and/or kern_clock.c.  */
   65 struct callout *callout;
   66 struct callout_list callfree;
   67 int callwheelsize, callwheelbits, callwheelmask;
   68 struct callout_tailq *callwheel;
   69 int softticks;                  /* Like ticks, but for softclock(). */
   70 struct mtx callout_lock;
   71 #ifdef DIAGNOSTIC
   72 struct mtx dont_sleep_in_callout;
   73 #endif
   74 
   75 static struct callout *nextsoftcheck;   /* Next callout to be checked. */
   76 
   77 /**
   78  * Locked by callout_lock:
   79  *   curr_callout    - If a callout is in progress, it is curr_callout.
   80  *                     If curr_callout is non-NULL, threads waiting on
   81  *                     callout_wait will be woken up as soon as the 
   82  *                     relevant callout completes.
   83  *   curr_cancelled  - Changing to 1 with both callout_lock and Giant held
   84  *                     guarantees that the current callout will not run.
   85  *                     The softclock() function sets this to 0 before it
   86  *                     drops callout_lock to acquire Giant, and it calls
   87  *                     the handler only if curr_cancelled still 0 when
   88  *                     Giant is successfully acquired.
   89  *   wakeup_ctr      - Incremented every time a thread wants to wait
   90  *                     for a callout to complete.  Modified only when
   91  *                     curr_callout is non-NULL.
   92  *   wakeup_needed   - If a thread is waiting on callout_wait, then
   93  *                     wakeup_needed is nonzero.  Increased only when
   94  *                     cutt_callout is non-NULL.
   95  */
   96 static struct callout *curr_callout;
   97 static int curr_cancelled;
   98 static int wakeup_ctr;
   99 static int wakeup_needed;
  100 
  101 /**
  102  * Locked by callout_wait_lock:
  103  *   callout_wait    - If wakeup_needed is set, callout_wait will be
  104  *                     triggered after the current callout finishes.
  105  *   wakeup_done_ctr - Set to the current value of wakeup_ctr after
  106  *                     callout_wait is triggered.
  107  */
  108 static struct mtx callout_wait_lock;
  109 static struct cv callout_wait;
  110 static int wakeup_done_ctr;
  111 
  112 /*
  113  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  114  *
  115  *      This code is called very early in the kernel initialization sequence,
  116  *      and may be called more then once.
  117  */
  118 caddr_t
  119 kern_timeout_callwheel_alloc(caddr_t v)
  120 {
  121         /*
  122          * Calculate callout wheel size
  123          */
  124         for (callwheelsize = 1, callwheelbits = 0;
  125              callwheelsize < ncallout;
  126              callwheelsize <<= 1, ++callwheelbits)
  127                 ;
  128         callwheelmask = callwheelsize - 1;
  129 
  130         callout = (struct callout *)v;
  131         v = (caddr_t)(callout + ncallout);
  132         callwheel = (struct callout_tailq *)v;
  133         v = (caddr_t)(callwheel + callwheelsize);
  134         return(v);
  135 }
  136 
  137 /*
  138  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  139  *                                 space.
  140  *
  141  *      This code is called just once, after the space reserved for the
  142  *      callout wheel has been finalized.
  143  */
  144 void
  145 kern_timeout_callwheel_init(void)
  146 {
  147         int i;
  148 
  149         SLIST_INIT(&callfree);
  150         for (i = 0; i < ncallout; i++) {
  151                 callout_init(&callout[i], 0);
  152                 callout[i].c_flags = CALLOUT_LOCAL_ALLOC;
  153                 SLIST_INSERT_HEAD(&callfree, &callout[i], c_links.sle);
  154         }
  155         for (i = 0; i < callwheelsize; i++) {
  156                 TAILQ_INIT(&callwheel[i]);
  157         }
  158         mtx_init(&callout_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  159 #ifdef DIAGNOSTIC
  160         mtx_init(&dont_sleep_in_callout, "dont_sleep_in_callout", NULL, MTX_DEF);
  161 #endif
  162         mtx_init(&callout_wait_lock, "callout_wait_lock", NULL, MTX_DEF);
  163         cv_init(&callout_wait, "callout_wait");
  164 }
  165 
  166 /*
  167  * The callout mechanism is based on the work of Adam M. Costello and 
  168  * George Varghese, published in a technical report entitled "Redesigning
  169  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  170  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  171  * used in this implementation was published by G. Varghese and T. Lauck in
  172  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  173  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  174  * the 11th ACM Annual Symposium on Operating Systems Principles,
  175  * Austin, Texas Nov 1987.
  176  */
  177 
  178 /*
  179  * Software (low priority) clock interrupt.
  180  * Run periodic events from timeout queue.
  181  */
  182 void
  183 softclock(void *dummy)
  184 {
  185         struct callout *c;
  186         struct callout_tailq *bucket;
  187         int curticks;
  188         int steps;      /* #steps since we last allowed interrupts */
  189         int depth;
  190         int mpcalls;
  191         int gcalls;
  192         int wakeup_cookie;
  193 #ifdef DIAGNOSTIC
  194         struct bintime bt1, bt2;
  195         struct timespec ts2;
  196         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  197         static timeout_t *lastfunc;
  198 #endif
  199 
  200 #ifndef MAX_SOFTCLOCK_STEPS
  201 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  202 #endif /* MAX_SOFTCLOCK_STEPS */
  203 
  204         mpcalls = 0;
  205         gcalls = 0;
  206         depth = 0;
  207         steps = 0;
  208         mtx_lock_spin(&callout_lock);
  209         while (softticks != ticks) {
  210                 softticks++;
  211                 /*
  212                  * softticks may be modified by hard clock, so cache
  213                  * it while we work on a given bucket.
  214                  */
  215                 curticks = softticks;
  216                 bucket = &callwheel[curticks & callwheelmask];
  217                 c = TAILQ_FIRST(bucket);
  218                 while (c) {
  219                         depth++;
  220                         if (c->c_time != curticks) {
  221                                 c = TAILQ_NEXT(c, c_links.tqe);
  222                                 ++steps;
  223                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  224                                         nextsoftcheck = c;
  225                                         /* Give interrupts a chance. */
  226                                         mtx_unlock_spin(&callout_lock);
  227                                         ;       /* nothing */
  228                                         mtx_lock_spin(&callout_lock);
  229                                         c = nextsoftcheck;
  230                                         steps = 0;
  231                                 }
  232                         } else {
  233                                 void (*c_func)(void *);
  234                                 void *c_arg;
  235                                 int c_flags;
  236 
  237                                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  238                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  239                                 c_func = c->c_func;
  240                                 c_arg = c->c_arg;
  241                                 c_flags = c->c_flags;
  242                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  243                                         c->c_func = NULL;
  244                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  245                                         SLIST_INSERT_HEAD(&callfree, c,
  246                                                           c_links.sle);
  247                                         curr_callout = NULL;
  248                                 } else {
  249                                         c->c_flags =
  250                                             (c->c_flags & ~CALLOUT_PENDING);
  251                                         curr_callout = c;
  252                                 }
  253                                 curr_cancelled = 0;
  254                                 mtx_unlock_spin(&callout_lock);
  255                                 if (!(c_flags & CALLOUT_MPSAFE)) {
  256                                         mtx_lock(&Giant);
  257                                         /*
  258                                          * The callout may have been cancelled
  259                                          * while we switched locks.
  260                                          */
  261                                         if (curr_cancelled) {
  262                                                 mtx_unlock(&Giant);
  263                                                 mtx_lock_spin(&callout_lock);
  264                                                 goto done_locked;
  265                                         }
  266                                         /* The callout cannot be stopped now. */
  267                                         curr_cancelled = 1;
  268                                         gcalls++;
  269                                         CTR1(KTR_CALLOUT, "callout %p", c_func);
  270                                 } else {
  271                                         mpcalls++;
  272                                         CTR1(KTR_CALLOUT, "callout mpsafe %p",
  273                                             c_func);
  274                                 }
  275 #ifdef DIAGNOSTIC
  276                                 binuptime(&bt1);
  277                                 mtx_lock(&dont_sleep_in_callout);
  278 #endif
  279                                 c_func(c_arg);
  280 #ifdef DIAGNOSTIC
  281                                 mtx_unlock(&dont_sleep_in_callout);
  282                                 binuptime(&bt2);
  283                                 bintime_sub(&bt2, &bt1);
  284                                 if (bt2.frac > maxdt) {
  285                                         if (lastfunc != c_func ||
  286                                             bt2.frac > maxdt * 2) {
  287                                                 bintime2timespec(&bt2, &ts2);
  288                                                 printf(
  289                         "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  290                                                     c_func, c_arg,
  291                                                     (intmax_t)ts2.tv_sec,
  292                                                     ts2.tv_nsec);
  293                                         }
  294                                         maxdt = bt2.frac;
  295                                         lastfunc = c_func;
  296                                 }
  297 #endif
  298                                 if (!(c_flags & CALLOUT_MPSAFE))
  299                                         mtx_unlock(&Giant);
  300                                 mtx_lock_spin(&callout_lock);
  301 done_locked:
  302                                 curr_callout = NULL;
  303                                 if (wakeup_needed) {
  304                                         /*
  305                                          * There might be someone waiting
  306                                          * for the callout to complete.
  307                                          */
  308                                         wakeup_cookie = wakeup_ctr;
  309                                         mtx_unlock_spin(&callout_lock);
  310                                         mtx_lock(&callout_wait_lock);
  311                                         cv_broadcast(&callout_wait);
  312                                         wakeup_done_ctr = wakeup_cookie;
  313                                         mtx_unlock(&callout_wait_lock);
  314                                         mtx_lock_spin(&callout_lock);
  315                                         wakeup_needed = 0;
  316                                 }
  317                                 steps = 0;
  318                                 c = nextsoftcheck;
  319                         }
  320                 }
  321         }
  322         avg_depth += (depth * 1000 - avg_depth) >> 8;
  323         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  324         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  325         nextsoftcheck = NULL;
  326         mtx_unlock_spin(&callout_lock);
  327 }
  328 
  329 /*
  330  * timeout --
  331  *      Execute a function after a specified length of time.
  332  *
  333  * untimeout --
  334  *      Cancel previous timeout function call.
  335  *
  336  * callout_handle_init --
  337  *      Initialize a handle so that using it with untimeout is benign.
  338  *
  339  *      See AT&T BCI Driver Reference Manual for specification.  This
  340  *      implementation differs from that one in that although an 
  341  *      identification value is returned from timeout, the original
  342  *      arguments to timeout as well as the identifier are used to
  343  *      identify entries for untimeout.
  344  */
  345 struct callout_handle
  346 timeout(ftn, arg, to_ticks)
  347         timeout_t *ftn;
  348         void *arg;
  349         int to_ticks;
  350 {
  351         struct callout *new;
  352         struct callout_handle handle;
  353 
  354         mtx_lock_spin(&callout_lock);
  355 
  356         /* Fill in the next free callout structure. */
  357         new = SLIST_FIRST(&callfree);
  358         if (new == NULL)
  359                 /* XXX Attempt to malloc first */
  360                 panic("timeout table full");
  361         SLIST_REMOVE_HEAD(&callfree, c_links.sle);
  362         
  363         callout_reset(new, to_ticks, ftn, arg);
  364 
  365         handle.callout = new;
  366         mtx_unlock_spin(&callout_lock);
  367         return (handle);
  368 }
  369 
  370 void
  371 untimeout(ftn, arg, handle)
  372         timeout_t *ftn;
  373         void *arg;
  374         struct callout_handle handle;
  375 {
  376 
  377         /*
  378          * Check for a handle that was initialized
  379          * by callout_handle_init, but never used
  380          * for a real timeout.
  381          */
  382         if (handle.callout == NULL)
  383                 return;
  384 
  385         mtx_lock_spin(&callout_lock);
  386         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  387                 callout_stop(handle.callout);
  388         mtx_unlock_spin(&callout_lock);
  389 }
  390 
  391 void
  392 callout_handle_init(struct callout_handle *handle)
  393 {
  394         handle->callout = NULL;
  395 }
  396 
  397 /*
  398  * New interface; clients allocate their own callout structures.
  399  *
  400  * callout_reset() - establish or change a timeout
  401  * callout_stop() - disestablish a timeout
  402  * callout_init() - initialize a callout structure so that it can
  403  *      safely be passed to callout_reset() and callout_stop()
  404  *
  405  * <sys/callout.h> defines three convenience macros:
  406  *
  407  * callout_active() - returns truth if callout has not been serviced
  408  * callout_pending() - returns truth if callout is still waiting for timeout
  409  * callout_deactivate() - marks the callout as having been serviced
  410  */
  411 void
  412 callout_reset(c, to_ticks, ftn, arg)
  413         struct  callout *c;
  414         int     to_ticks;
  415         void    (*ftn)(void *);
  416         void    *arg;
  417 {
  418 
  419         mtx_lock_spin(&callout_lock);
  420         if (c == curr_callout) {
  421                 /*
  422                  * We're being asked to reschedule a callout which is
  423                  * currently in progress.  If there is a mutex then we
  424                  * can cancel the callout if it has not really started.
  425                  */
  426                 if ((c->c_flags & CALLOUT_MPSAFE) == 0 && !curr_cancelled)
  427                         curr_cancelled = 1;
  428                 if (wakeup_needed) {
  429                         /*
  430                          * Someone has called callout_drain to kill this
  431                          * callout.  Don't reschedule.
  432                          */
  433                         mtx_unlock_spin(&callout_lock);
  434                         return;
  435                 }
  436         }
  437         if (c->c_flags & CALLOUT_PENDING) {
  438                 if (nextsoftcheck == c) {
  439                         nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  440                 }
  441                 TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c,
  442                     c_links.tqe);
  443 
  444                 /*
  445                  * Part of the normal "stop a pending callout" process
  446                  * is to clear the CALLOUT_ACTIVE and CALLOUT_PENDING
  447                  * flags.  We're not going to bother doing that here,
  448                  * because we're going to be setting those flags ten lines
  449                  * after this point, and we're holding callout_lock
  450                  * between now and then.
  451                  */
  452         }
  453 
  454         /*
  455          * We could unlock callout_lock here and lock it again before the
  456          * TAILQ_INSERT_TAIL, but there's no point since doing this setup
  457          * doesn't take much time.
  458          */
  459         if (to_ticks <= 0)
  460                 to_ticks = 1;
  461 
  462         c->c_arg = arg;
  463         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  464         c->c_func = ftn;
  465         c->c_time = ticks + to_ticks;
  466         TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
  467                           c, c_links.tqe);
  468         mtx_unlock_spin(&callout_lock);
  469 }
  470 
  471 int
  472 _callout_stop_safe(c, safe)
  473         struct  callout *c;
  474         int     safe;
  475 {
  476         int use_mtx, wakeup_cookie;
  477 
  478         if (!safe && (c->c_flags & CALLOUT_MPSAFE) == 0) {
  479                 use_mtx = mtx_owned(&Giant);
  480         } else {
  481                 use_mtx = 0;
  482         }
  483 
  484         mtx_lock_spin(&callout_lock);
  485         /*
  486          * Don't attempt to delete a callout that's not on the queue.
  487          */
  488         if (!(c->c_flags & CALLOUT_PENDING)) {
  489                 c->c_flags &= ~CALLOUT_ACTIVE;
  490                 if (c != curr_callout) {
  491                         mtx_unlock_spin(&callout_lock);
  492                         return (0);
  493                 }
  494                 if (safe) {
  495                         /* We need to wait until the callout is finished. */
  496                         wakeup_needed = 1;
  497                         wakeup_cookie = wakeup_ctr++;
  498                         mtx_unlock_spin(&callout_lock);
  499                         mtx_lock(&callout_wait_lock);
  500 
  501                         /*
  502                          * Check to make sure that softclock() didn't
  503                          * do the wakeup in between our dropping
  504                          * callout_lock and picking up callout_wait_lock
  505                          */
  506                         if (wakeup_cookie - wakeup_done_ctr > 0)
  507                                 cv_wait(&callout_wait, &callout_wait_lock);
  508 
  509                         mtx_unlock(&callout_wait_lock);
  510                 } else if (use_mtx && !curr_cancelled) {
  511                         /* We can stop the callout before it runs. */
  512                         curr_cancelled = 1;
  513                         mtx_unlock_spin(&callout_lock);
  514                         return (1);
  515                 } else
  516                         mtx_unlock_spin(&callout_lock);
  517                 return (0);
  518         }
  519         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  520 
  521         if (nextsoftcheck == c) {
  522                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  523         }
  524         TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
  525 
  526         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  527                 c->c_func = NULL;
  528                 SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
  529         }
  530         mtx_unlock_spin(&callout_lock);
  531         return (1);
  532 }
  533 
  534 void
  535 callout_init(c, mpsafe)
  536         struct  callout *c;
  537         int mpsafe;
  538 {
  539         bzero(c, sizeof *c);
  540         if (mpsafe)
  541                 c->c_flags |= CALLOUT_MPSAFE;
  542 }
  543 
  544 #ifdef APM_FIXUP_CALLTODO
  545 /* 
  546  * Adjust the kernel calltodo timeout list.  This routine is used after 
  547  * an APM resume to recalculate the calltodo timer list values with the 
  548  * number of hz's we have been sleeping.  The next hardclock() will detect 
  549  * that there are fired timers and run softclock() to execute them.
  550  *
  551  * Please note, I have not done an exhaustive analysis of what code this
  552  * might break.  I am motivated to have my select()'s and alarm()'s that
  553  * have expired during suspend firing upon resume so that the applications
  554  * which set the timer can do the maintanence the timer was for as close
  555  * as possible to the originally intended time.  Testing this code for a 
  556  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  557  * firing, which seemed independant on whether the suspend was 2 hours or
  558  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  559  */
  560 void
  561 adjust_timeout_calltodo(time_change)
  562     struct timeval *time_change;
  563 {
  564         register struct callout *p;
  565         unsigned long delta_ticks;
  566 
  567         /* 
  568          * How many ticks were we asleep?
  569          * (stolen from tvtohz()).
  570          */
  571 
  572         /* Don't do anything */
  573         if (time_change->tv_sec < 0)
  574                 return;
  575         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  576                 delta_ticks = (time_change->tv_sec * 1000000 +
  577                                time_change->tv_usec + (tick - 1)) / tick + 1;
  578         else if (time_change->tv_sec <= LONG_MAX / hz)
  579                 delta_ticks = time_change->tv_sec * hz +
  580                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  581         else
  582                 delta_ticks = LONG_MAX;
  583 
  584         if (delta_ticks > INT_MAX)
  585                 delta_ticks = INT_MAX;
  586 
  587         /* 
  588          * Now rip through the timer calltodo list looking for timers
  589          * to expire.
  590          */
  591 
  592         /* don't collide with softclock() */
  593         mtx_lock_spin(&callout_lock);
  594         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  595                 p->c_time -= delta_ticks;
  596 
  597                 /* Break if the timer had more time on it than delta_ticks */
  598                 if (p->c_time > 0)
  599                         break;
  600 
  601                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  602                 delta_ticks = -p->c_time;
  603         }
  604         mtx_unlock_spin(&callout_lock);
  605 
  606         return;
  607 }
  608 #endif /* APM_FIXUP_CALLTODO */

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