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/5.3/sys/kern/kern_timeout.c 136588 2004-10-16 08:43:07Z cvs2svn $");
   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  *   wakeup_ctr      - Incremented every time a thread wants to wait
   84  *                     for a callout to complete.  Modified only when
   85  *                     curr_callout is non-NULL.
   86  *   wakeup_needed   - If a thread is waiting on callout_wait, then
   87  *                     wakeup_needed is nonzero.  Increased only when
   88  *                     cutt_callout is non-NULL.
   89  */
   90 static struct callout *curr_callout;
   91 static int wakeup_ctr;
   92 static int wakeup_needed;
   93 
   94 /*-
   95  * Locked by callout_wait_lock:
   96  *   callout_wait    - If wakeup_needed is set, callout_wait will be
   97  *                     triggered after the current callout finishes.
   98  *   wakeup_done_ctr - Set to the current value of wakeup_ctr after
   99  *                     callout_wait is triggered.
  100  */
  101 static struct mtx callout_wait_lock;
  102 static struct cv callout_wait;
  103 static int wakeup_done_ctr;
  104 
  105 /*
  106  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  107  *
  108  *      This code is called very early in the kernel initialization sequence,
  109  *      and may be called more then once.
  110  */
  111 caddr_t
  112 kern_timeout_callwheel_alloc(caddr_t v)
  113 {
  114         /*
  115          * Calculate callout wheel size
  116          */
  117         for (callwheelsize = 1, callwheelbits = 0;
  118              callwheelsize < ncallout;
  119              callwheelsize <<= 1, ++callwheelbits)
  120                 ;
  121         callwheelmask = callwheelsize - 1;
  122 
  123         callout = (struct callout *)v;
  124         v = (caddr_t)(callout + ncallout);
  125         callwheel = (struct callout_tailq *)v;
  126         v = (caddr_t)(callwheel + callwheelsize);
  127         return(v);
  128 }
  129 
  130 /*
  131  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  132  *                                 space.
  133  *
  134  *      This code is called just once, after the space reserved for the
  135  *      callout wheel has been finalized.
  136  */
  137 void
  138 kern_timeout_callwheel_init(void)
  139 {
  140         int i;
  141 
  142         SLIST_INIT(&callfree);
  143         for (i = 0; i < ncallout; i++) {
  144                 callout_init(&callout[i], 0);
  145                 callout[i].c_flags = CALLOUT_LOCAL_ALLOC;
  146                 SLIST_INSERT_HEAD(&callfree, &callout[i], c_links.sle);
  147         }
  148         for (i = 0; i < callwheelsize; i++) {
  149                 TAILQ_INIT(&callwheel[i]);
  150         }
  151         mtx_init(&callout_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  152 #ifdef DIAGNOSTIC
  153         mtx_init(&dont_sleep_in_callout, "dont_sleep_in_callout", NULL, MTX_DEF);
  154 #endif
  155         mtx_init(&callout_wait_lock, "callout_wait_lock", NULL, MTX_DEF);
  156         cv_init(&callout_wait, "callout_wait");
  157 }
  158 
  159 /*
  160  * The callout mechanism is based on the work of Adam M. Costello and 
  161  * George Varghese, published in a technical report entitled "Redesigning
  162  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  163  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  164  * used in this implementation was published by G. Varghese and T. Lauck in
  165  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  166  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  167  * the 11th ACM Annual Symposium on Operating Systems Principles,
  168  * Austin, Texas Nov 1987.
  169  */
  170 
  171 /*
  172  * Software (low priority) clock interrupt.
  173  * Run periodic events from timeout queue.
  174  */
  175 void
  176 softclock(void *dummy)
  177 {
  178         struct callout *c;
  179         struct callout_tailq *bucket;
  180         int curticks;
  181         int steps;      /* #steps since we last allowed interrupts */
  182         int depth;
  183         int mpcalls;
  184         int gcalls;
  185         int wakeup_cookie;
  186 #ifdef DIAGNOSTIC
  187         struct bintime bt1, bt2;
  188         struct timespec ts2;
  189         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  190         static timeout_t *lastfunc;
  191 #endif
  192 
  193 #ifndef MAX_SOFTCLOCK_STEPS
  194 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  195 #endif /* MAX_SOFTCLOCK_STEPS */
  196 
  197         mpcalls = 0;
  198         gcalls = 0;
  199         depth = 0;
  200         steps = 0;
  201         mtx_lock_spin(&callout_lock);
  202         while (softticks != ticks) {
  203                 softticks++;
  204                 /*
  205                  * softticks may be modified by hard clock, so cache
  206                  * it while we work on a given bucket.
  207                  */
  208                 curticks = softticks;
  209                 bucket = &callwheel[curticks & callwheelmask];
  210                 c = TAILQ_FIRST(bucket);
  211                 while (c) {
  212                         depth++;
  213                         if (c->c_time != curticks) {
  214                                 c = TAILQ_NEXT(c, c_links.tqe);
  215                                 ++steps;
  216                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  217                                         nextsoftcheck = c;
  218                                         /* Give interrupts a chance. */
  219                                         mtx_unlock_spin(&callout_lock);
  220                                         ;       /* nothing */
  221                                         mtx_lock_spin(&callout_lock);
  222                                         c = nextsoftcheck;
  223                                         steps = 0;
  224                                 }
  225                         } else {
  226                                 void (*c_func)(void *);
  227                                 void *c_arg;
  228                                 int c_flags;
  229 
  230                                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  231                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  232                                 c_func = c->c_func;
  233                                 c_arg = c->c_arg;
  234                                 c_flags = c->c_flags;
  235                                 c->c_func = NULL;
  236                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  237                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  238                                         SLIST_INSERT_HEAD(&callfree, c,
  239                                                           c_links.sle);
  240                                 } else {
  241                                         c->c_flags =
  242                                             (c->c_flags & ~CALLOUT_PENDING);
  243                                 }
  244                                 curr_callout = c;
  245                                 mtx_unlock_spin(&callout_lock);
  246                                 if (!(c_flags & CALLOUT_MPSAFE)) {
  247                                         mtx_lock(&Giant);
  248                                         gcalls++;
  249                                         CTR1(KTR_CALLOUT, "callout %p", c_func);
  250                                 } else {
  251                                         mpcalls++;
  252                                         CTR1(KTR_CALLOUT, "callout mpsafe %p",
  253                                             c_func);
  254                                 }
  255 #ifdef DIAGNOSTIC
  256                                 binuptime(&bt1);
  257                                 mtx_lock(&dont_sleep_in_callout);
  258 #endif
  259                                 c_func(c_arg);
  260 #ifdef DIAGNOSTIC
  261                                 mtx_unlock(&dont_sleep_in_callout);
  262                                 binuptime(&bt2);
  263                                 bintime_sub(&bt2, &bt1);
  264                                 if (bt2.frac > maxdt) {
  265                                         if (lastfunc != c_func ||
  266                                             bt2.frac > maxdt * 2) {
  267                                                 bintime2timespec(&bt2, &ts2);
  268                                                 printf(
  269                         "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  270                                                     c_func, c_arg,
  271                                                     (intmax_t)ts2.tv_sec,
  272                                                     ts2.tv_nsec);
  273                                         }
  274                                         maxdt = bt2.frac;
  275                                         lastfunc = c_func;
  276                                 }
  277 #endif
  278                                 if (!(c_flags & CALLOUT_MPSAFE))
  279                                         mtx_unlock(&Giant);
  280                                 mtx_lock_spin(&callout_lock);
  281                                 curr_callout = NULL;
  282                                 if (wakeup_needed) {
  283                                         /*
  284                                          * There might be someone waiting
  285                                          * for the callout to complete.
  286                                          */
  287                                         wakeup_cookie = wakeup_ctr;
  288                                         mtx_unlock_spin(&callout_lock);
  289                                         mtx_lock(&callout_wait_lock);
  290                                         cv_broadcast(&callout_wait);
  291                                         wakeup_done_ctr = wakeup_cookie;
  292                                         mtx_unlock(&callout_wait_lock);
  293                                         mtx_lock_spin(&callout_lock);
  294                                         wakeup_needed = 0;
  295                                 }
  296                                 steps = 0;
  297                                 c = nextsoftcheck;
  298                         }
  299                 }
  300         }
  301         avg_depth += (depth * 1000 - avg_depth) >> 8;
  302         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  303         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  304         nextsoftcheck = NULL;
  305         mtx_unlock_spin(&callout_lock);
  306 }
  307 
  308 /*
  309  * timeout --
  310  *      Execute a function after a specified length of time.
  311  *
  312  * untimeout --
  313  *      Cancel previous timeout function call.
  314  *
  315  * callout_handle_init --
  316  *      Initialize a handle so that using it with untimeout is benign.
  317  *
  318  *      See AT&T BCI Driver Reference Manual for specification.  This
  319  *      implementation differs from that one in that although an 
  320  *      identification value is returned from timeout, the original
  321  *      arguments to timeout as well as the identifier are used to
  322  *      identify entries for untimeout.
  323  */
  324 struct callout_handle
  325 timeout(ftn, arg, to_ticks)
  326         timeout_t *ftn;
  327         void *arg;
  328         int to_ticks;
  329 {
  330         struct callout *new;
  331         struct callout_handle handle;
  332 
  333         mtx_lock_spin(&callout_lock);
  334 
  335         /* Fill in the next free callout structure. */
  336         new = SLIST_FIRST(&callfree);
  337         if (new == NULL)
  338                 /* XXX Attempt to malloc first */
  339                 panic("timeout table full");
  340         SLIST_REMOVE_HEAD(&callfree, c_links.sle);
  341         
  342         callout_reset(new, to_ticks, ftn, arg);
  343 
  344         handle.callout = new;
  345         mtx_unlock_spin(&callout_lock);
  346         return (handle);
  347 }
  348 
  349 void
  350 untimeout(ftn, arg, handle)
  351         timeout_t *ftn;
  352         void *arg;
  353         struct callout_handle handle;
  354 {
  355 
  356         /*
  357          * Check for a handle that was initialized
  358          * by callout_handle_init, but never used
  359          * for a real timeout.
  360          */
  361         if (handle.callout == NULL)
  362                 return;
  363 
  364         mtx_lock_spin(&callout_lock);
  365         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  366                 callout_stop(handle.callout);
  367         mtx_unlock_spin(&callout_lock);
  368 }
  369 
  370 void
  371 callout_handle_init(struct callout_handle *handle)
  372 {
  373         handle->callout = NULL;
  374 }
  375 
  376 /*
  377  * New interface; clients allocate their own callout structures.
  378  *
  379  * callout_reset() - establish or change a timeout
  380  * callout_stop() - disestablish a timeout
  381  * callout_init() - initialize a callout structure so that it can
  382  *      safely be passed to callout_reset() and callout_stop()
  383  *
  384  * <sys/callout.h> defines three convenience macros:
  385  *
  386  * callout_active() - returns truth if callout has not been serviced
  387  * callout_pending() - returns truth if callout is still waiting for timeout
  388  * callout_deactivate() - marks the callout as having been serviced
  389  */
  390 void
  391 callout_reset(c, to_ticks, ftn, arg)
  392         struct  callout *c;
  393         int     to_ticks;
  394         void    (*ftn)(void *);
  395         void    *arg;
  396 {
  397 
  398         mtx_lock_spin(&callout_lock);
  399         if (c == curr_callout && wakeup_needed) {
  400                 /*
  401                  * We're being asked to reschedule a callout which is
  402                  * currently in progress, and someone has called
  403                  * callout_drain to kill that callout.  Don't reschedule.
  404                  */
  405                 mtx_unlock_spin(&callout_lock);
  406                 return;
  407         }
  408         if (c->c_flags & CALLOUT_PENDING) {
  409                 if (nextsoftcheck == c) {
  410                         nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  411                 }
  412                 TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c,
  413                     c_links.tqe);
  414 
  415                 /*
  416                  * Part of the normal "stop a pending callout" process
  417                  * is to clear the CALLOUT_ACTIVE and CALLOUT_PENDING
  418                  * flags.  We're not going to bother doing that here,
  419                  * because we're going to be setting those flags ten lines
  420                  * after this point, and we're holding callout_lock
  421                  * between now and then.
  422                  */
  423         }
  424 
  425         /*
  426          * We could unlock callout_lock here and lock it again before the
  427          * TAILQ_INSERT_TAIL, but there's no point since doing this setup
  428          * doesn't take much time.
  429          */
  430         if (to_ticks <= 0)
  431                 to_ticks = 1;
  432 
  433         c->c_arg = arg;
  434         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  435         c->c_func = ftn;
  436         c->c_time = ticks + to_ticks;
  437         TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
  438                           c, c_links.tqe);
  439         mtx_unlock_spin(&callout_lock);
  440 }
  441 
  442 int
  443 _callout_stop_safe(c, safe)
  444         struct  callout *c;
  445         int     safe;
  446 {
  447         int wakeup_cookie;
  448 
  449         mtx_lock_spin(&callout_lock);
  450         /*
  451          * Don't attempt to delete a callout that's not on the queue.
  452          */
  453         if (!(c->c_flags & CALLOUT_PENDING)) {
  454                 c->c_flags &= ~CALLOUT_ACTIVE;
  455                 if (c == curr_callout && safe) {
  456                         /* We need to wait until the callout is finished. */
  457                         wakeup_needed = 1;
  458                         wakeup_cookie = wakeup_ctr++;
  459                         mtx_unlock_spin(&callout_lock);
  460                         mtx_lock(&callout_wait_lock);
  461 
  462                         /*
  463                          * Check to make sure that softclock() didn't
  464                          * do the wakeup in between our dropping
  465                          * callout_lock and picking up callout_wait_lock
  466                          */
  467                         if (wakeup_cookie - wakeup_done_ctr > 0)
  468                                 cv_wait(&callout_wait, &callout_wait_lock);
  469 
  470                         mtx_unlock(&callout_wait_lock);
  471                 } else
  472                         mtx_unlock_spin(&callout_lock);
  473                 return (0);
  474         }
  475         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  476 
  477         if (nextsoftcheck == c) {
  478                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  479         }
  480         TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
  481         c->c_func = NULL;
  482 
  483         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  484                 SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
  485         }
  486         mtx_unlock_spin(&callout_lock);
  487         return (1);
  488 }
  489 
  490 void
  491 callout_init(c, mpsafe)
  492         struct  callout *c;
  493         int mpsafe;
  494 {
  495         bzero(c, sizeof *c);
  496         if (mpsafe)
  497                 c->c_flags |= CALLOUT_MPSAFE;
  498 }
  499 
  500 #ifdef APM_FIXUP_CALLTODO
  501 /* 
  502  * Adjust the kernel calltodo timeout list.  This routine is used after 
  503  * an APM resume to recalculate the calltodo timer list values with the 
  504  * number of hz's we have been sleeping.  The next hardclock() will detect 
  505  * that there are fired timers and run softclock() to execute them.
  506  *
  507  * Please note, I have not done an exhaustive analysis of what code this
  508  * might break.  I am motivated to have my select()'s and alarm()'s that
  509  * have expired during suspend firing upon resume so that the applications
  510  * which set the timer can do the maintanence the timer was for as close
  511  * as possible to the originally intended time.  Testing this code for a 
  512  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  513  * firing, which seemed independant on whether the suspend was 2 hours or
  514  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  515  */
  516 void
  517 adjust_timeout_calltodo(time_change)
  518     struct timeval *time_change;
  519 {
  520         register struct callout *p;
  521         unsigned long delta_ticks;
  522 
  523         /* 
  524          * How many ticks were we asleep?
  525          * (stolen from tvtohz()).
  526          */
  527 
  528         /* Don't do anything */
  529         if (time_change->tv_sec < 0)
  530                 return;
  531         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  532                 delta_ticks = (time_change->tv_sec * 1000000 +
  533                                time_change->tv_usec + (tick - 1)) / tick + 1;
  534         else if (time_change->tv_sec <= LONG_MAX / hz)
  535                 delta_ticks = time_change->tv_sec * hz +
  536                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  537         else
  538                 delta_ticks = LONG_MAX;
  539 
  540         if (delta_ticks > INT_MAX)
  541                 delta_ticks = INT_MAX;
  542 
  543         /* 
  544          * Now rip through the timer calltodo list looking for timers
  545          * to expire.
  546          */
  547 
  548         /* don't collide with softclock() */
  549         mtx_lock_spin(&callout_lock);
  550         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  551                 p->c_time -= delta_ticks;
  552 
  553                 /* Break if the timer had more time on it than delta_ticks */
  554                 if (p->c_time > 0)
  555                         break;
  556 
  557                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  558                 delta_ticks = -p->c_time;
  559         }
  560         mtx_unlock_spin(&callout_lock);
  561 
  562         return;
  563 }
  564 #endif /* APM_FIXUP_CALLTODO */

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