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: stable/3/sys/kern/kern_timeout.c 50583 1999-08-29 16:33:42Z peter $
   40  */
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/callout.h>
   45 #include <sys/kernel.h>
   46 
   47 /*
   48  * TODO:
   49  *      allocate more timeout table slots when table overflows.
   50  */
   51 
   52 /* Exported to machdep.c and/or kern_clock.c.  */
   53 struct callout *callout;
   54 struct callout_list callfree;
   55 int callwheelsize, callwheelbits, callwheelmask;
   56 struct callout_tailq *callwheel;
   57 int softticks;                  /* Like ticks, but for softclock(). */
   58 
   59 static struct callout *nextsoftcheck;   /* Next callout to be checked. */
   60 
   61 /*
   62  * The callout mechanism is based on the work of Adam M. Costello and 
   63  * George Varghese, published in a technical report entitled "Redesigning
   64  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
   65  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
   66  * used in this implementation was published by G.Varghese and A. Lauck in
   67  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
   68  * the Efficient Implementation of a Timer Facility" in the Proceedings of
   69  * the 11th ACM Annual Symposium on Operating Systems Principles,
   70  * Austin, Texas Nov 1987.
   71  */
   72 
   73 /*
   74  * Software (low priority) clock interrupt.
   75  * Run periodic events from timeout queue.
   76  */
   77 void
   78 softclock()
   79 {
   80         register struct callout *c;
   81         register struct callout_tailq *bucket;
   82         register int s;
   83         register int curticks;
   84         register int steps;     /* #steps since we last allowed interrupts */
   85 
   86 #ifndef MAX_SOFTCLOCK_STEPS
   87 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
   88 #endif /* MAX_SOFTCLOCK_STEPS */
   89 
   90         steps = 0;
   91         s = splhigh();
   92         while (softticks != ticks) {
   93                 softticks++;
   94                 /*
   95                  * softticks may be modified by hard clock, so cache
   96                  * it while we work on a given bucket.
   97                  */
   98                 curticks = softticks;
   99                 bucket = &callwheel[curticks & callwheelmask];
  100                 c = TAILQ_FIRST(bucket);
  101                 while (c) {
  102                         if (c->c_time != curticks) {
  103                                 c = TAILQ_NEXT(c, c_links.tqe);
  104                                 ++steps;
  105                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  106                                         nextsoftcheck = c;
  107                                         /* Give interrupts a chance. */
  108                                         splx(s);
  109                                         s = splhigh();
  110                                         c = nextsoftcheck;
  111                                         steps = 0;
  112                                 }
  113                         } else {
  114                                 void (*c_func)(void *);
  115                                 void *c_arg;
  116 
  117                                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  118                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  119                                 c_func = c->c_func;
  120                                 c_arg = c->c_arg;
  121                                 c->c_func = NULL;
  122                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  123                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  124                                         SLIST_INSERT_HEAD(&callfree, c,
  125                                                           c_links.sle);
  126                                 } else {
  127                                         c->c_flags =
  128                                                 (c->c_flags & ~CALLOUT_PENDING)
  129                                                 | CALLOUT_FIRED;
  130                                 }
  131                                 splx(s);
  132                                 c_func(c_arg);
  133                                 s = splhigh();
  134                                 steps = 0;
  135                                 c = nextsoftcheck;
  136                         }
  137                 }
  138         }
  139         nextsoftcheck = NULL;
  140         splx(s);
  141 }
  142 
  143 /*
  144  * timeout --
  145  *      Execute a function after a specified length of time.
  146  *
  147  * untimeout --
  148  *      Cancel previous timeout function call.
  149  *
  150  * callout_handle_init --
  151  *      Initialize a handle so that using it with untimeout is benign.
  152  *
  153  *      See AT&T BCI Driver Reference Manual for specification.  This
  154  *      implementation differs from that one in that although an 
  155  *      identification value is returned from timeout, the original
  156  *      arguments to timeout as well as the identifier are used to
  157  *      identify entries for untimeout.
  158  */
  159 struct callout_handle
  160 timeout(ftn, arg, to_ticks)
  161         timeout_t *ftn;
  162         void *arg;
  163         register int to_ticks;
  164 {
  165         int s;
  166         struct callout *new;
  167         struct callout_handle handle;
  168 
  169         s = splhigh();
  170 
  171         /* Fill in the next free callout structure. */
  172         new = SLIST_FIRST(&callfree);
  173         if (new == NULL)
  174                 /* XXX Attempt to malloc first */
  175                 panic("timeout table full");
  176         SLIST_REMOVE_HEAD(&callfree, c_links.sle);
  177         
  178         callout_reset(new, to_ticks, ftn, arg);
  179 
  180         handle.callout = new;
  181         splx(s);
  182         return (handle);
  183 }
  184 
  185 void
  186 untimeout(ftn, arg, handle)
  187         timeout_t *ftn;
  188         void *arg;
  189         struct callout_handle handle;
  190 {
  191         register int s;
  192 
  193         /*
  194          * Check for a handle that was initialized
  195          * by callout_handle_init, but never used
  196          * for a real timeout.
  197          */
  198         if (handle.callout == NULL)
  199                 return;
  200 
  201         s = splhigh();
  202         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  203                 callout_stop(handle.callout);
  204         splx(s);
  205 }
  206 
  207 void
  208 callout_handle_init(struct callout_handle *handle)
  209 {
  210         handle->callout = NULL;
  211 }
  212 
  213 /*
  214  * New interface; clients allocate their own callout structures.
  215  *
  216  * callout_reset() - establish or change a timeout
  217  * callout_stop() - disestablish a timeout
  218  * callout_init() - initialize a callout structure so that it can
  219  *      safely be passed to callout_reset() and callout_stop()
  220  *
  221  * <sys/callout.h> defines two convenience macros:
  222  *
  223  * callout_pending() - returns number of ticks until callout fires, or 0
  224  *      if not scheduled
  225  * callout_fired() - returns truth if callout has already been fired
  226  */
  227 void
  228 callout_reset(c, to_ticks, ftn, arg)
  229         struct  callout *c;
  230         int     to_ticks;
  231         void    (*ftn) __P((void *));
  232         void    *arg;
  233 {
  234         int     s;
  235 
  236         s = splhigh();
  237         if (c->c_flags & CALLOUT_PENDING)
  238                 callout_stop(c);
  239 
  240         /*
  241          * We could spl down here and back up at the TAILQ_INSERT_TAIL,
  242          * but there's no point since doing this setup doesn't take much
  243          ^ time.
  244          */
  245         if (to_ticks <= 0)
  246                 to_ticks = 1;
  247 
  248         c->c_arg = arg;
  249         c->c_flags = (c->c_flags & ~CALLOUT_FIRED) | CALLOUT_PENDING;
  250         c->c_func = ftn;
  251         c->c_time = ticks + to_ticks;
  252         TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
  253                           c, c_links.tqe);
  254         splx(s);
  255         
  256 }
  257 
  258 void
  259 callout_stop(c)
  260         struct  callout *c;
  261 {
  262         int     s;
  263 
  264         s = splhigh();
  265         /*
  266          * Don't attempt to delete a callout that's not on the queue.
  267          */
  268         if (!(c->c_flags & CALLOUT_PENDING)) {
  269                 splx(s);
  270                 return;
  271         }
  272         c->c_flags &= ~CALLOUT_PENDING;
  273 
  274         if (nextsoftcheck == c) {
  275                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  276         }
  277         TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
  278         c->c_func = NULL;
  279 
  280         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  281                 SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
  282         }
  283         splx(s);
  284 }
  285 
  286 void
  287 callout_init(c)
  288         struct  callout *c;
  289 {
  290         bzero(c, sizeof c);
  291 }
  292 
  293 #ifdef APM_FIXUP_CALLTODO
  294 /* 
  295  * Adjust the kernel calltodo timeout list.  This routine is used after 
  296  * an APM resume to recalculate the calltodo timer list values with the 
  297  * number of hz's we have been sleeping.  The next hardclock() will detect 
  298  * that there are fired timers and run softclock() to execute them.
  299  *
  300  * Please note, I have not done an exhaustive analysis of what code this
  301  * might break.  I am motivated to have my select()'s and alarm()'s that
  302  * have expired during suspend firing upon resume so that the applications
  303  * which set the timer can do the maintanence the timer was for as close
  304  * as possible to the originally intended time.  Testing this code for a 
  305  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  306  * firing, which seemed independant on whether the suspend was 2 hours or
  307  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  308  */
  309 void
  310 adjust_timeout_calltodo(time_change)
  311     struct timeval *time_change;
  312 {
  313         register struct callout *p;
  314         unsigned long delta_ticks;
  315         int s;
  316 
  317         /* 
  318          * How many ticks were we asleep?
  319          * (stolen from tvtohz()).
  320          */
  321 
  322         /* Don't do anything */
  323         if (time_change->tv_sec < 0)
  324                 return;
  325         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  326                 delta_ticks = (time_change->tv_sec * 1000000 +
  327                                time_change->tv_usec + (tick - 1)) / tick + 1;
  328         else if (time_change->tv_sec <= LONG_MAX / hz)
  329                 delta_ticks = time_change->tv_sec * hz +
  330                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  331         else
  332                 delta_ticks = LONG_MAX;
  333 
  334         if (delta_ticks > INT_MAX)
  335                 delta_ticks = INT_MAX;
  336 
  337         /* 
  338          * Now rip through the timer calltodo list looking for timers
  339          * to expire.
  340          */
  341 
  342         /* don't collide with softclock() */
  343         s = splhigh(); 
  344         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  345                 p->c_time -= delta_ticks;
  346 
  347                 /* Break if the timer had more time on it than delta_ticks */
  348                 if (p->c_time > 0)
  349                         break;
  350 
  351                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  352                 delta_ticks = -p->c_time;
  353         }
  354         splx(s);
  355 
  356         return;
  357 }
  358 #endif /* APM_FIXUP_CALLTODO */

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