The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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: releng/6.0/sys/kern/kern_timeout.c 150591 2005-09-26 19:49:12Z jhb $");
   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/proc.h>
   49 #include <sys/sysctl.h>
   50 
   51 static int avg_depth;
   52 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
   53     "Average number of items examined per softclock call. Units = 1/1000");
   54 static int avg_gcalls;
   55 SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
   56     "Average number of Giant callouts made per softclock call. Units = 1/1000");
   57 static int avg_mtxcalls;
   58 SYSCTL_INT(_debug, OID_AUTO, to_avg_mtxcalls, CTLFLAG_RD, &avg_mtxcalls, 0,
   59     "Average number of mtx callouts made per softclock call. Units = 1/1000");
   60 static int avg_mpcalls;
   61 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
   62     "Average number of MP callouts made per softclock call. Units = 1/1000");
   63 /*
   64  * TODO:
   65  *      allocate more timeout table slots when table overflows.
   66  */
   67 
   68 /* Exported to machdep.c and/or kern_clock.c.  */
   69 struct callout *callout;
   70 struct callout_list callfree;
   71 int callwheelsize, callwheelbits, callwheelmask;
   72 struct callout_tailq *callwheel;
   73 int softticks;                  /* Like ticks, but for softclock(). */
   74 struct mtx callout_lock;
   75 
   76 static struct callout *nextsoftcheck;   /* Next callout to be checked. */
   77 
   78 /**
   79  * Locked by callout_lock:
   80  *   curr_callout    - If a callout is in progress, it is curr_callout.
   81  *                     If curr_callout is non-NULL, threads waiting on
   82  *                     callout_wait will be woken up as soon as the 
   83  *                     relevant callout completes.
   84  *   curr_cancelled  - Changing to 1 with both callout_lock and c_mtx held
   85  *                     guarantees that the current callout will not run.
   86  *                     The softclock() function sets this to 0 before it
   87  *                     drops callout_lock to acquire c_mtx, and it calls
   88  *                     the handler only if curr_cancelled still 0 when
   89  *                     c_mtx is successfully acquired.
   90  *   wakeup_ctr      - Incremented every time a thread wants to wait
   91  *                     for a callout to complete.  Modified only when
   92  *                     curr_callout is non-NULL.
   93  *   wakeup_needed   - If a thread is waiting on callout_wait, then
   94  *                     wakeup_needed is nonzero.  Increased only when
   95  *                     cutt_callout is non-NULL.
   96  */
   97 static struct callout *curr_callout;
   98 static int curr_cancelled;
   99 static int wakeup_ctr;
  100 static int wakeup_needed;
  101 
  102 /**
  103  * Locked by callout_wait_lock:
  104  *   callout_wait    - If wakeup_needed is set, callout_wait will be
  105  *                     triggered after the current callout finishes.
  106  *   wakeup_done_ctr - Set to the current value of wakeup_ctr after
  107  *                     callout_wait is triggered.
  108  */
  109 static struct mtx callout_wait_lock;
  110 static struct cv callout_wait;
  111 static int wakeup_done_ctr;
  112 
  113 /*
  114  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  115  *
  116  *      This code is called very early in the kernel initialization sequence,
  117  *      and may be called more then once.
  118  */
  119 caddr_t
  120 kern_timeout_callwheel_alloc(caddr_t v)
  121 {
  122         /*
  123          * Calculate callout wheel size
  124          */
  125         for (callwheelsize = 1, callwheelbits = 0;
  126              callwheelsize < ncallout;
  127              callwheelsize <<= 1, ++callwheelbits)
  128                 ;
  129         callwheelmask = callwheelsize - 1;
  130 
  131         callout = (struct callout *)v;
  132         v = (caddr_t)(callout + ncallout);
  133         callwheel = (struct callout_tailq *)v;
  134         v = (caddr_t)(callwheel + callwheelsize);
  135         return(v);
  136 }
  137 
  138 /*
  139  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  140  *                                 space.
  141  *
  142  *      This code is called just once, after the space reserved for the
  143  *      callout wheel has been finalized.
  144  */
  145 void
  146 kern_timeout_callwheel_init(void)
  147 {
  148         int i;
  149 
  150         SLIST_INIT(&callfree);
  151         for (i = 0; i < ncallout; i++) {
  152                 callout_init(&callout[i], 0);
  153                 callout[i].c_flags = CALLOUT_LOCAL_ALLOC;
  154                 SLIST_INSERT_HEAD(&callfree, &callout[i], c_links.sle);
  155         }
  156         for (i = 0; i < callwheelsize; i++) {
  157                 TAILQ_INIT(&callwheel[i]);
  158         }
  159         mtx_init(&callout_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  160         mtx_init(&callout_wait_lock, "callout_wait_lock", NULL, MTX_DEF);
  161         cv_init(&callout_wait, "callout_wait");
  162 }
  163 
  164 /*
  165  * The callout mechanism is based on the work of Adam M. Costello and 
  166  * George Varghese, published in a technical report entitled "Redesigning
  167  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  168  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  169  * used in this implementation was published by G. Varghese and T. Lauck in
  170  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  171  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  172  * the 11th ACM Annual Symposium on Operating Systems Principles,
  173  * Austin, Texas Nov 1987.
  174  */
  175 
  176 /*
  177  * Software (low priority) clock interrupt.
  178  * Run periodic events from timeout queue.
  179  */
  180 void
  181 softclock(void *dummy)
  182 {
  183         struct callout *c;
  184         struct callout_tailq *bucket;
  185         int curticks;
  186         int steps;      /* #steps since we last allowed interrupts */
  187         int depth;
  188         int mpcalls;
  189         int mtxcalls;
  190         int gcalls;
  191         int wakeup_cookie;
  192 #ifdef DIAGNOSTIC
  193         struct bintime bt1, bt2;
  194         struct timespec ts2;
  195         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  196         static timeout_t *lastfunc;
  197 #endif
  198 
  199 #ifndef MAX_SOFTCLOCK_STEPS
  200 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  201 #endif /* MAX_SOFTCLOCK_STEPS */
  202 
  203         mpcalls = 0;
  204         mtxcalls = 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                                 struct mtx *c_mtx;
  236                                 int c_flags;
  237 
  238                                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  239                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  240                                 c_func = c->c_func;
  241                                 c_arg = c->c_arg;
  242                                 c_mtx = c->c_mtx;
  243                                 c_flags = c->c_flags;
  244                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  245                                         c->c_func = NULL;
  246                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  247                                         SLIST_INSERT_HEAD(&callfree, c,
  248                                                           c_links.sle);
  249                                         curr_callout = NULL;
  250                                 } else {
  251                                         c->c_flags =
  252                                             (c->c_flags & ~CALLOUT_PENDING);
  253                                         curr_callout = c;
  254                                 }
  255                                 curr_cancelled = 0;
  256                                 mtx_unlock_spin(&callout_lock);
  257                                 if (c_mtx != NULL) {
  258                                         mtx_lock(c_mtx);
  259                                         /*
  260                                          * The callout may have been cancelled
  261                                          * while we switched locks.
  262                                          */
  263                                         if (curr_cancelled) {
  264                                                 mtx_unlock(c_mtx);
  265                                                 mtx_lock_spin(&callout_lock);
  266                                                 goto done_locked;
  267                                         }
  268                                         /* The callout cannot be stopped now. */
  269                                         curr_cancelled = 1;
  270 
  271                                         if (c_mtx == &Giant) {
  272                                                 gcalls++;
  273                                                 CTR1(KTR_CALLOUT, "callout %p",
  274                                                     c_func);
  275                                         } else {
  276                                                 mtxcalls++;
  277                                                 CTR1(KTR_CALLOUT,
  278                                                     "callout mtx %p",
  279                                                     c_func);
  280                                         }
  281                                 } else {
  282                                         mpcalls++;
  283                                         CTR1(KTR_CALLOUT, "callout mpsafe %p",
  284                                             c_func);
  285                                 }
  286 #ifdef DIAGNOSTIC
  287                                 binuptime(&bt1);
  288 #endif
  289                                 THREAD_NO_SLEEPING();
  290                                 c_func(c_arg);
  291                                 THREAD_SLEEPING_OK();
  292 #ifdef DIAGNOSTIC
  293                                 binuptime(&bt2);
  294                                 bintime_sub(&bt2, &bt1);
  295                                 if (bt2.frac > maxdt) {
  296                                         if (lastfunc != c_func ||
  297                                             bt2.frac > maxdt * 2) {
  298                                                 bintime2timespec(&bt2, &ts2);
  299                                                 printf(
  300                         "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  301                                                     c_func, c_arg,
  302                                                     (intmax_t)ts2.tv_sec,
  303                                                     ts2.tv_nsec);
  304                                         }
  305                                         maxdt = bt2.frac;
  306                                         lastfunc = c_func;
  307                                 }
  308 #endif
  309                                 if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
  310                                         mtx_unlock(c_mtx);
  311                                 mtx_lock_spin(&callout_lock);
  312 done_locked:
  313                                 curr_callout = NULL;
  314                                 if (wakeup_needed) {
  315                                         /*
  316                                          * There might be someone waiting
  317                                          * for the callout to complete.
  318                                          */
  319                                         wakeup_cookie = wakeup_ctr;
  320                                         mtx_unlock_spin(&callout_lock);
  321                                         mtx_lock(&callout_wait_lock);
  322                                         cv_broadcast(&callout_wait);
  323                                         wakeup_done_ctr = wakeup_cookie;
  324                                         mtx_unlock(&callout_wait_lock);
  325                                         mtx_lock_spin(&callout_lock);
  326                                         wakeup_needed = 0;
  327                                 }
  328                                 steps = 0;
  329                                 c = nextsoftcheck;
  330                         }
  331                 }
  332         }
  333         avg_depth += (depth * 1000 - avg_depth) >> 8;
  334         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  335         avg_mtxcalls += (mtxcalls * 1000 - avg_mtxcalls) >> 8;
  336         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  337         nextsoftcheck = NULL;
  338         mtx_unlock_spin(&callout_lock);
  339 }
  340 
  341 /*
  342  * timeout --
  343  *      Execute a function after a specified length of time.
  344  *
  345  * untimeout --
  346  *      Cancel previous timeout function call.
  347  *
  348  * callout_handle_init --
  349  *      Initialize a handle so that using it with untimeout is benign.
  350  *
  351  *      See AT&T BCI Driver Reference Manual for specification.  This
  352  *      implementation differs from that one in that although an 
  353  *      identification value is returned from timeout, the original
  354  *      arguments to timeout as well as the identifier are used to
  355  *      identify entries for untimeout.
  356  */
  357 struct callout_handle
  358 timeout(ftn, arg, to_ticks)
  359         timeout_t *ftn;
  360         void *arg;
  361         int to_ticks;
  362 {
  363         struct callout *new;
  364         struct callout_handle handle;
  365 
  366         mtx_lock_spin(&callout_lock);
  367 
  368         /* Fill in the next free callout structure. */
  369         new = SLIST_FIRST(&callfree);
  370         if (new == NULL)
  371                 /* XXX Attempt to malloc first */
  372                 panic("timeout table full");
  373         SLIST_REMOVE_HEAD(&callfree, c_links.sle);
  374         
  375         callout_reset(new, to_ticks, ftn, arg);
  376 
  377         handle.callout = new;
  378         mtx_unlock_spin(&callout_lock);
  379         return (handle);
  380 }
  381 
  382 void
  383 untimeout(ftn, arg, handle)
  384         timeout_t *ftn;
  385         void *arg;
  386         struct callout_handle handle;
  387 {
  388 
  389         /*
  390          * Check for a handle that was initialized
  391          * by callout_handle_init, but never used
  392          * for a real timeout.
  393          */
  394         if (handle.callout == NULL)
  395                 return;
  396 
  397         mtx_lock_spin(&callout_lock);
  398         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  399                 callout_stop(handle.callout);
  400         mtx_unlock_spin(&callout_lock);
  401 }
  402 
  403 void
  404 callout_handle_init(struct callout_handle *handle)
  405 {
  406         handle->callout = NULL;
  407 }
  408 
  409 /*
  410  * New interface; clients allocate their own callout structures.
  411  *
  412  * callout_reset() - establish or change a timeout
  413  * callout_stop() - disestablish a timeout
  414  * callout_init() - initialize a callout structure so that it can
  415  *      safely be passed to callout_reset() and callout_stop()
  416  *
  417  * <sys/callout.h> defines three convenience macros:
  418  *
  419  * callout_active() - returns truth if callout has not been stopped,
  420  *      drained, or deactivated since the last time the callout was
  421  *      reset.
  422  * callout_pending() - returns truth if callout is still waiting for timeout
  423  * callout_deactivate() - marks the callout as having been serviced
  424  */
  425 int
  426 callout_reset(c, to_ticks, ftn, arg)
  427         struct  callout *c;
  428         int     to_ticks;
  429         void    (*ftn)(void *);
  430         void    *arg;
  431 {
  432         int cancelled = 0;
  433 
  434 #ifdef notyet /* Some callers of timeout() do not hold Giant. */
  435         if (c->c_mtx != NULL)
  436                 mtx_assert(c->c_mtx, MA_OWNED);
  437 #endif
  438 
  439         mtx_lock_spin(&callout_lock);
  440         if (c == curr_callout) {
  441                 /*
  442                  * We're being asked to reschedule a callout which is
  443                  * currently in progress.  If there is a mutex then we
  444                  * can cancel the callout if it has not really started.
  445                  */
  446                 if (c->c_mtx != NULL && !curr_cancelled)
  447                         cancelled = curr_cancelled = 1;
  448                 if (wakeup_needed) {
  449                         /*
  450                          * Someone has called callout_drain to kill this
  451                          * callout.  Don't reschedule.
  452                          */
  453                         mtx_unlock_spin(&callout_lock);
  454                         return (cancelled);
  455                 }
  456         }
  457         if (c->c_flags & CALLOUT_PENDING) {
  458                 if (nextsoftcheck == c) {
  459                         nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  460                 }
  461                 TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c,
  462                     c_links.tqe);
  463 
  464                 cancelled = 1;
  465 
  466                 /*
  467                  * Part of the normal "stop a pending callout" process
  468                  * is to clear the CALLOUT_ACTIVE and CALLOUT_PENDING
  469                  * flags.  We're not going to bother doing that here,
  470                  * because we're going to be setting those flags ten lines
  471                  * after this point, and we're holding callout_lock
  472                  * between now and then.
  473                  */
  474         }
  475 
  476         /*
  477          * We could unlock callout_lock here and lock it again before the
  478          * TAILQ_INSERT_TAIL, but there's no point since doing this setup
  479          * doesn't take much time.
  480          */
  481         if (to_ticks <= 0)
  482                 to_ticks = 1;
  483 
  484         c->c_arg = arg;
  485         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  486         c->c_func = ftn;
  487         c->c_time = ticks + to_ticks;
  488         TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
  489                           c, c_links.tqe);
  490         mtx_unlock_spin(&callout_lock);
  491 
  492         return (cancelled);
  493 }
  494 
  495 int
  496 _callout_stop_safe(c, safe)
  497         struct  callout *c;
  498         int     safe;
  499 {
  500         int use_mtx, wakeup_cookie;
  501 
  502         if (!safe && c->c_mtx != NULL) {
  503 #ifdef notyet /* Some callers do not hold Giant for Giant-locked callouts. */
  504                 mtx_assert(c->c_mtx, MA_OWNED);
  505                 use_mtx = 1;
  506 #else
  507                 use_mtx = mtx_owned(c->c_mtx);
  508 #endif
  509         } else {
  510                 use_mtx = 0;
  511         }
  512 
  513         mtx_lock_spin(&callout_lock);
  514         /*
  515          * Don't attempt to delete a callout that's not on the queue.
  516          */
  517         if (!(c->c_flags & CALLOUT_PENDING)) {
  518                 c->c_flags &= ~CALLOUT_ACTIVE;
  519                 if (c != curr_callout) {
  520                         mtx_unlock_spin(&callout_lock);
  521                         return (0);
  522                 }
  523                 if (safe) {
  524                         /* We need to wait until the callout is finished. */
  525                         wakeup_needed = 1;
  526                         wakeup_cookie = wakeup_ctr++;
  527                         mtx_unlock_spin(&callout_lock);
  528                         mtx_lock(&callout_wait_lock);
  529 
  530                         /*
  531                          * Check to make sure that softclock() didn't
  532                          * do the wakeup in between our dropping
  533                          * callout_lock and picking up callout_wait_lock
  534                          */
  535                         if (wakeup_cookie - wakeup_done_ctr > 0)
  536                                 cv_wait(&callout_wait, &callout_wait_lock);
  537 
  538                         mtx_unlock(&callout_wait_lock);
  539                 } else if (use_mtx && !curr_cancelled) {
  540                         /* We can stop the callout before it runs. */
  541                         curr_cancelled = 1;
  542                         mtx_unlock_spin(&callout_lock);
  543                         return (1);
  544                 } else
  545                         mtx_unlock_spin(&callout_lock);
  546                 return (0);
  547         }
  548         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  549 
  550         if (nextsoftcheck == c) {
  551                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  552         }
  553         TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
  554 
  555         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  556                 c->c_func = NULL;
  557                 SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
  558         }
  559         mtx_unlock_spin(&callout_lock);
  560         return (1);
  561 }
  562 
  563 void
  564 callout_init(c, mpsafe)
  565         struct  callout *c;
  566         int mpsafe;
  567 {
  568         bzero(c, sizeof *c);
  569         if (mpsafe) {
  570                 c->c_mtx = NULL;
  571                 c->c_flags = CALLOUT_RETURNUNLOCKED;
  572         } else {
  573                 c->c_mtx = &Giant;
  574                 c->c_flags = 0;
  575         }
  576 }
  577 
  578 void
  579 callout_init_mtx(c, mtx, flags)
  580         struct  callout *c;
  581         struct  mtx *mtx;
  582         int flags;
  583 {
  584         bzero(c, sizeof *c);
  585         c->c_mtx = mtx;
  586         KASSERT((flags & ~CALLOUT_RETURNUNLOCKED) == 0,
  587             ("callout_init_mtx: bad flags %d", flags));
  588         /* CALLOUT_RETURNUNLOCKED makes no sense without a mutex. */
  589         KASSERT(mtx != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
  590             ("callout_init_mtx: CALLOUT_RETURNUNLOCKED with no mutex"));
  591         c->c_flags = flags & CALLOUT_RETURNUNLOCKED;
  592 }
  593 
  594 #ifdef APM_FIXUP_CALLTODO
  595 /* 
  596  * Adjust the kernel calltodo timeout list.  This routine is used after 
  597  * an APM resume to recalculate the calltodo timer list values with the 
  598  * number of hz's we have been sleeping.  The next hardclock() will detect 
  599  * that there are fired timers and run softclock() to execute them.
  600  *
  601  * Please note, I have not done an exhaustive analysis of what code this
  602  * might break.  I am motivated to have my select()'s and alarm()'s that
  603  * have expired during suspend firing upon resume so that the applications
  604  * which set the timer can do the maintanence the timer was for as close
  605  * as possible to the originally intended time.  Testing this code for a 
  606  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  607  * firing, which seemed independant on whether the suspend was 2 hours or
  608  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  609  */
  610 void
  611 adjust_timeout_calltodo(time_change)
  612     struct timeval *time_change;
  613 {
  614         register struct callout *p;
  615         unsigned long delta_ticks;
  616 
  617         /* 
  618          * How many ticks were we asleep?
  619          * (stolen from tvtohz()).
  620          */
  621 
  622         /* Don't do anything */
  623         if (time_change->tv_sec < 0)
  624                 return;
  625         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  626                 delta_ticks = (time_change->tv_sec * 1000000 +
  627                                time_change->tv_usec + (tick - 1)) / tick + 1;
  628         else if (time_change->tv_sec <= LONG_MAX / hz)
  629                 delta_ticks = time_change->tv_sec * hz +
  630                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  631         else
  632                 delta_ticks = LONG_MAX;
  633 
  634         if (delta_ticks > INT_MAX)
  635                 delta_ticks = INT_MAX;
  636 
  637         /* 
  638          * Now rip through the timer calltodo list looking for timers
  639          * to expire.
  640          */
  641 
  642         /* don't collide with softclock() */
  643         mtx_lock_spin(&callout_lock);
  644         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  645                 p->c_time -= delta_ticks;
  646 
  647                 /* Break if the timer had more time on it than delta_ticks */
  648                 if (p->c_time > 0)
  649                         break;
  650 
  651                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  652                 delta_ticks = -p->c_time;
  653         }
  654         mtx_unlock_spin(&callout_lock);
  655 
  656         return;
  657 }
  658 #endif /* APM_FIXUP_CALLTODO */

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