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  * 3. All advertising materials mentioning features or use of this software
   19  *    must display the following acknowledgement:
   20  *      This product includes software developed by the University of
   21  *      California, Berkeley and its contributors.
   22  * 4. Neither the name of the University nor the names of its contributors
   23  *    may be used to endorse or promote products derived from this software
   24  *    without specific prior written permission.
   25  *
   26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   36  * SUCH DAMAGE.
   37  *
   38  *      From: @(#)kern_clock.c  8.5 (Berkeley) 1/21/94
   39  * $FreeBSD: releng/5.0/sys/kern/kern_timeout.c 102961 2002-09-05 11:42:03Z phk $
   40  */
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/callout.h>
   45 #include <sys/kernel.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 
   49 /*
   50  * TODO:
   51  *      allocate more timeout table slots when table overflows.
   52  */
   53 
   54 /* Exported to machdep.c and/or kern_clock.c.  */
   55 struct callout *callout;
   56 struct callout_list callfree;
   57 int callwheelsize, callwheelbits, callwheelmask;
   58 struct callout_tailq *callwheel;
   59 int softticks;                  /* Like ticks, but for softclock(). */
   60 struct mtx callout_lock;
   61 
   62 static struct callout *nextsoftcheck;   /* Next callout to be checked. */
   63 
   64 /*
   65  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
   66  *
   67  *      This code is called very early in the kernel initialization sequence,
   68  *      and may be called more then once.
   69  */
   70 caddr_t
   71 kern_timeout_callwheel_alloc(caddr_t v)
   72 {
   73         /*
   74          * Calculate callout wheel size
   75          */
   76         for (callwheelsize = 1, callwheelbits = 0;
   77              callwheelsize < ncallout;
   78              callwheelsize <<= 1, ++callwheelbits)
   79                 ;
   80         callwheelmask = callwheelsize - 1;
   81 
   82         callout = (struct callout *)v;
   83         v = (caddr_t)(callout + ncallout);
   84         callwheel = (struct callout_tailq *)v;
   85         v = (caddr_t)(callwheel + callwheelsize);
   86         return(v);
   87 }
   88 
   89 /*
   90  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
   91  *                                 space.
   92  *
   93  *      This code is called just once, after the space reserved for the
   94  *      callout wheel has been finalized.
   95  */
   96 void
   97 kern_timeout_callwheel_init(void)
   98 {
   99         int i;
  100 
  101         SLIST_INIT(&callfree);
  102         for (i = 0; i < ncallout; i++) {
  103                 callout_init(&callout[i], 0);
  104                 callout[i].c_flags = CALLOUT_LOCAL_ALLOC;
  105                 SLIST_INSERT_HEAD(&callfree, &callout[i], c_links.sle);
  106         }
  107         for (i = 0; i < callwheelsize; i++) {
  108                 TAILQ_INIT(&callwheel[i]);
  109         }
  110         mtx_init(&callout_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  111 }
  112 
  113 /*
  114  * The callout mechanism is based on the work of Adam M. Costello and 
  115  * George Varghese, published in a technical report entitled "Redesigning
  116  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  117  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  118  * used in this implementation was published by G.Varghese and A. Lauck in
  119  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  120  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  121  * the 11th ACM Annual Symposium on Operating Systems Principles,
  122  * Austin, Texas Nov 1987.
  123  */
  124 
  125 /*
  126  * Software (low priority) clock interrupt.
  127  * Run periodic events from timeout queue.
  128  */
  129 void
  130 softclock(void *dummy)
  131 {
  132         struct callout *c;
  133         struct callout_tailq *bucket;
  134         int curticks;
  135         int steps;      /* #steps since we last allowed interrupts */
  136 #ifdef DIAGNOSTIC
  137         struct bintime bt1, bt2;
  138         struct timespec ts2;
  139         static uint64_t maxdt = 18446744073709551LL;    /* 1 msec */
  140 #endif
  141 
  142 #ifndef MAX_SOFTCLOCK_STEPS
  143 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  144 #endif /* MAX_SOFTCLOCK_STEPS */
  145 
  146         steps = 0;
  147         mtx_lock_spin(&callout_lock);
  148         while (softticks != ticks) {
  149                 softticks++;
  150                 /*
  151                  * softticks may be modified by hard clock, so cache
  152                  * it while we work on a given bucket.
  153                  */
  154                 curticks = softticks;
  155                 bucket = &callwheel[curticks & callwheelmask];
  156                 c = TAILQ_FIRST(bucket);
  157                 while (c) {
  158                         if (c->c_time != curticks) {
  159                                 c = TAILQ_NEXT(c, c_links.tqe);
  160                                 ++steps;
  161                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  162                                         nextsoftcheck = c;
  163                                         /* Give interrupts a chance. */
  164                                         mtx_unlock_spin(&callout_lock);
  165                                         ;       /* nothing */
  166                                         mtx_lock_spin(&callout_lock);
  167                                         c = nextsoftcheck;
  168                                         steps = 0;
  169                                 }
  170                         } else {
  171                                 void (*c_func)(void *);
  172                                 void *c_arg;
  173                                 int c_flags;
  174 
  175                                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  176                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  177                                 c_func = c->c_func;
  178                                 c_arg = c->c_arg;
  179                                 c_flags = c->c_flags;
  180                                 c->c_func = NULL;
  181                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  182                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  183                                         SLIST_INSERT_HEAD(&callfree, c,
  184                                                           c_links.sle);
  185                                 } else {
  186                                         c->c_flags =
  187                                             (c->c_flags & ~CALLOUT_PENDING);
  188                                 }
  189                                 mtx_unlock_spin(&callout_lock);
  190                                 if (!(c_flags & CALLOUT_MPSAFE))
  191                                         mtx_lock(&Giant);
  192 #ifdef DIAGNOSTIC
  193                                 binuptime(&bt1);
  194 #endif
  195                                 c_func(c_arg);
  196 #ifdef DIAGNOSTIC
  197                                 binuptime(&bt2);
  198                                 bintime_sub(&bt2, &bt1);
  199                                 if (bt2.frac > maxdt) {
  200                                         bintime2timespec(&bt2, &ts2);
  201                                         printf(
  202                         "Expensive timeout(9) function: %p(%p) %d.%09ld\n",
  203                                         c_func, c_arg,
  204                                         ts2.tv_sec, ts2.tv_nsec);
  205                                 }
  206 #endif
  207                                 if (!(c_flags & CALLOUT_MPSAFE))
  208                                         mtx_unlock(&Giant);
  209                                 mtx_lock_spin(&callout_lock);
  210                                 steps = 0;
  211                                 c = nextsoftcheck;
  212                         }
  213                 }
  214         }
  215         nextsoftcheck = NULL;
  216         mtx_unlock_spin(&callout_lock);
  217 }
  218 
  219 /*
  220  * timeout --
  221  *      Execute a function after a specified length of time.
  222  *
  223  * untimeout --
  224  *      Cancel previous timeout function call.
  225  *
  226  * callout_handle_init --
  227  *      Initialize a handle so that using it with untimeout is benign.
  228  *
  229  *      See AT&T BCI Driver Reference Manual for specification.  This
  230  *      implementation differs from that one in that although an 
  231  *      identification value is returned from timeout, the original
  232  *      arguments to timeout as well as the identifier are used to
  233  *      identify entries for untimeout.
  234  */
  235 struct callout_handle
  236 timeout(ftn, arg, to_ticks)
  237         timeout_t *ftn;
  238         void *arg;
  239         int to_ticks;
  240 {
  241         struct callout *new;
  242         struct callout_handle handle;
  243 
  244         mtx_lock_spin(&callout_lock);
  245 
  246         /* Fill in the next free callout structure. */
  247         new = SLIST_FIRST(&callfree);
  248         if (new == NULL)
  249                 /* XXX Attempt to malloc first */
  250                 panic("timeout table full");
  251         SLIST_REMOVE_HEAD(&callfree, c_links.sle);
  252         
  253         callout_reset(new, to_ticks, ftn, arg);
  254 
  255         handle.callout = new;
  256         mtx_unlock_spin(&callout_lock);
  257         return (handle);
  258 }
  259 
  260 void
  261 untimeout(ftn, arg, handle)
  262         timeout_t *ftn;
  263         void *arg;
  264         struct callout_handle handle;
  265 {
  266 
  267         /*
  268          * Check for a handle that was initialized
  269          * by callout_handle_init, but never used
  270          * for a real timeout.
  271          */
  272         if (handle.callout == NULL)
  273                 return;
  274 
  275         mtx_lock_spin(&callout_lock);
  276         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  277                 callout_stop(handle.callout);
  278         mtx_unlock_spin(&callout_lock);
  279 }
  280 
  281 void
  282 callout_handle_init(struct callout_handle *handle)
  283 {
  284         handle->callout = NULL;
  285 }
  286 
  287 /*
  288  * New interface; clients allocate their own callout structures.
  289  *
  290  * callout_reset() - establish or change a timeout
  291  * callout_stop() - disestablish a timeout
  292  * callout_init() - initialize a callout structure so that it can
  293  *      safely be passed to callout_reset() and callout_stop()
  294  *
  295  * <sys/callout.h> defines three convenience macros:
  296  *
  297  * callout_active() - returns truth if callout has not been serviced
  298  * callout_pending() - returns truth if callout is still waiting for timeout
  299  * callout_deactivate() - marks the callout as having been serviced
  300  */
  301 void
  302 callout_reset(c, to_ticks, ftn, arg)
  303         struct  callout *c;
  304         int     to_ticks;
  305         void    (*ftn)(void *);
  306         void    *arg;
  307 {
  308 
  309         mtx_lock_spin(&callout_lock);
  310         if (c->c_flags & CALLOUT_PENDING)
  311                 callout_stop(c);
  312 
  313         /*
  314          * We could unlock callout_lock here and lock it again before the
  315          * TAILQ_INSERT_TAIL, but there's no point since doing this setup
  316          * doesn't take much time.
  317          */
  318         if (to_ticks <= 0)
  319                 to_ticks = 1;
  320 
  321         c->c_arg = arg;
  322         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  323         c->c_func = ftn;
  324         c->c_time = ticks + to_ticks;
  325         TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
  326                           c, c_links.tqe);
  327         mtx_unlock_spin(&callout_lock);
  328 }
  329 
  330 int
  331 callout_stop(c)
  332         struct  callout *c;
  333 {
  334 
  335         mtx_lock_spin(&callout_lock);
  336         /*
  337          * Don't attempt to delete a callout that's not on the queue.
  338          */
  339         if (!(c->c_flags & CALLOUT_PENDING)) {
  340                 c->c_flags &= ~CALLOUT_ACTIVE;
  341                 mtx_unlock_spin(&callout_lock);
  342                 return (0);
  343         }
  344         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  345 
  346         if (nextsoftcheck == c) {
  347                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  348         }
  349         TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
  350         c->c_func = NULL;
  351 
  352         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  353                 SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
  354         }
  355         mtx_unlock_spin(&callout_lock);
  356         return (1);
  357 }
  358 
  359 void
  360 callout_init(c, mpsafe)
  361         struct  callout *c;
  362         int mpsafe;
  363 {
  364         bzero(c, sizeof *c);
  365         if (mpsafe)
  366                 c->c_flags |= CALLOUT_MPSAFE;
  367 }
  368 
  369 #ifdef APM_FIXUP_CALLTODO
  370 /* 
  371  * Adjust the kernel calltodo timeout list.  This routine is used after 
  372  * an APM resume to recalculate the calltodo timer list values with the 
  373  * number of hz's we have been sleeping.  The next hardclock() will detect 
  374  * that there are fired timers and run softclock() to execute them.
  375  *
  376  * Please note, I have not done an exhaustive analysis of what code this
  377  * might break.  I am motivated to have my select()'s and alarm()'s that
  378  * have expired during suspend firing upon resume so that the applications
  379  * which set the timer can do the maintanence the timer was for as close
  380  * as possible to the originally intended time.  Testing this code for a 
  381  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  382  * firing, which seemed independant on whether the suspend was 2 hours or
  383  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  384  */
  385 void
  386 adjust_timeout_calltodo(time_change)
  387     struct timeval *time_change;
  388 {
  389         register struct callout *p;
  390         unsigned long delta_ticks;
  391 
  392         /* 
  393          * How many ticks were we asleep?
  394          * (stolen from tvtohz()).
  395          */
  396 
  397         /* Don't do anything */
  398         if (time_change->tv_sec < 0)
  399                 return;
  400         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  401                 delta_ticks = (time_change->tv_sec * 1000000 +
  402                                time_change->tv_usec + (tick - 1)) / tick + 1;
  403         else if (time_change->tv_sec <= LONG_MAX / hz)
  404                 delta_ticks = time_change->tv_sec * hz +
  405                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  406         else
  407                 delta_ticks = LONG_MAX;
  408 
  409         if (delta_ticks > INT_MAX)
  410                 delta_ticks = INT_MAX;
  411 
  412         /* 
  413          * Now rip through the timer calltodo list looking for timers
  414          * to expire.
  415          */
  416 
  417         /* don't collide with softclock() */
  418         mtx_lock_spin(&callout_lock);
  419         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  420                 p->c_time -= delta_ticks;
  421 
  422                 /* Break if the timer had more time on it than delta_ticks */
  423                 if (p->c_time > 0)
  424                         break;
  425 
  426                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  427                 delta_ticks = -p->c_time;
  428         }
  429         mtx_unlock_spin(&callout_lock);
  430 
  431         return;
  432 }
  433 #endif /* APM_FIXUP_CALLTODO */

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