FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_timeout.c

     /*-
      * Copyright (c) 1982, 1986, 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
      * the permission of UNIX System Laboratories, Inc.
      *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      From: @(#)kern_clock.c  8.5 (Berkeley) 1/21/94
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/5.2/sys/kern/kern_timeout.c 122761 2003-11-15 18:33:54Z phk $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/callout.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/sysctl.h>
    
    static int avg_depth;
    SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
        "Average number of items examined per softclock call. Units = 1/1000");
    static int avg_gcalls;
    SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
        "Average number of Giant callouts made per softclock call. Units = 1/1000");
    static int avg_mpcalls;
    SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
        "Average number of MP callouts made per softclock call. Units = 1/1000");
    /*
     * TODO:
     *      allocate more timeout table slots when table overflows.
     */
    
    /* Exported to machdep.c and/or kern_clock.c.  */
    struct callout *callout;
    struct callout_list callfree;
    int callwheelsize, callwheelbits, callwheelmask;
    struct callout_tailq *callwheel;
    int softticks;                  /* Like ticks, but for softclock(). */
    struct mtx callout_lock;
    #ifdef DIAGNOSTIC
    struct mtx dont_sleep_in_callout;
    #endif
    
    static struct callout *nextsoftcheck;   /* Next callout to be checked. */
    
    /*
     * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
     *
     *      This code is called very early in the kernel initialization sequence,
     *      and may be called more then once.
     */
    caddr_t
    kern_timeout_callwheel_alloc(caddr_t v)
    {
            /*
             * Calculate callout wheel size
             */
            for (callwheelsize = 1, callwheelbits = 0;
                 callwheelsize < ncallout;
                 callwheelsize <<= 1, ++callwheelbits)
                    ;
            callwheelmask = callwheelsize - 1;
    
            callout = (struct callout *)v;
            v = (caddr_t)(callout + ncallout);
            callwheel = (struct callout_tailq *)v;
           v = (caddr_t)(callwheel + callwheelsize);
           return(v);
   }
   
   /*
    * kern_timeout_callwheel_init() - initialize previously reserved callwheel
    *                                 space.
    *
    *      This code is called just once, after the space reserved for the
    *      callout wheel has been finalized.
    */
   void
   kern_timeout_callwheel_init(void)
   {
           int i;
   
           SLIST_INIT(&callfree);
           for (i = 0; i < ncallout; i++) {
                   callout_init(&callout[i], 0);
                   callout[i].c_flags = CALLOUT_LOCAL_ALLOC;
                   SLIST_INSERT_HEAD(&callfree, &callout[i], c_links.sle);
           }
           for (i = 0; i < callwheelsize; i++) {
                   TAILQ_INIT(&callwheel[i]);
           }
           mtx_init(&callout_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
   #ifdef DIAGNOSTIC
           mtx_init(&dont_sleep_in_callout, "dont_sleep_in_callout", NULL, MTX_DEF);
   #endif
   }
   
   /*
    * The callout mechanism is based on the work of Adam M. Costello and 
    * George Varghese, published in a technical report entitled "Redesigning
    * the BSD Callout and Timer Facilities" and modified slightly for inclusion
    * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
    * used in this implementation was published by G.Varghese and A. Lauck in
    * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
    * the Efficient Implementation of a Timer Facility" in the Proceedings of
    * the 11th ACM Annual Symposium on Operating Systems Principles,
    * Austin, Texas Nov 1987.
    */
   
   /*
    * Software (low priority) clock interrupt.
    * Run periodic events from timeout queue.
    */
   void
   softclock(void *dummy)
   {
           struct callout *c;
           struct callout_tailq *bucket;
           int curticks;
           int steps;      /* #steps since we last allowed interrupts */
           int depth;
           int mpcalls;
           int gcalls;
   #ifdef DIAGNOSTIC
           struct bintime bt1, bt2;
           struct timespec ts2;
           static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
   #endif
   
   #ifndef MAX_SOFTCLOCK_STEPS
   #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
   #endif /* MAX_SOFTCLOCK_STEPS */
   
           mpcalls = 0;
           gcalls = 0;
           depth = 0;
           steps = 0;
           mtx_lock_spin(&callout_lock);
           while (softticks != ticks) {
                   softticks++;
                   /*
                    * softticks may be modified by hard clock, so cache
                    * it while we work on a given bucket.
                    */
                   curticks = softticks;
                   bucket = &callwheel[curticks & callwheelmask];
                   c = TAILQ_FIRST(bucket);
                   while (c) {
                           depth++;
                           if (c->c_time != curticks) {
                                   c = TAILQ_NEXT(c, c_links.tqe);
                                   ++steps;
                                   if (steps >= MAX_SOFTCLOCK_STEPS) {
                                           nextsoftcheck = c;
                                           /* Give interrupts a chance. */
                                           mtx_unlock_spin(&callout_lock);
                                           ;       /* nothing */
                                           mtx_lock_spin(&callout_lock);
                                           c = nextsoftcheck;
                                           steps = 0;
                                   }
                           } else {
                                   void (*c_func)(void *);
                                   void *c_arg;
                                   int c_flags;
   
                                   nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
                                   TAILQ_REMOVE(bucket, c, c_links.tqe);
                                   c_func = c->c_func;
                                   c_arg = c->c_arg;
                                   c_flags = c->c_flags;
                                   c->c_func = NULL;
                                   if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
                                           c->c_flags = CALLOUT_LOCAL_ALLOC;
                                           SLIST_INSERT_HEAD(&callfree, c,
                                                             c_links.sle);
                                   } else {
                                           c->c_flags =
                                               (c->c_flags & ~CALLOUT_PENDING);
                                   }
                                   mtx_unlock_spin(&callout_lock);
                                   if (!(c_flags & CALLOUT_MPSAFE)) {
                                           mtx_lock(&Giant);
                                           gcalls++;
                                   } else {
                                           mpcalls++;
                                   }
   #ifdef DIAGNOSTIC
                                   binuptime(&bt1);
                                   mtx_lock(&dont_sleep_in_callout);
   #endif
                                   c_func(c_arg);
   #ifdef DIAGNOSTIC
                                   mtx_unlock(&dont_sleep_in_callout);
                                   binuptime(&bt2);
                                   bintime_sub(&bt2, &bt1);
                                   if (bt2.frac > maxdt) {
                                           maxdt = bt2.frac;
                                           bintime2timespec(&bt2, &ts2);
                                           printf(
                           "Expensive timeout(9) function: %p(%p) %ld.%09ld s\n",
                                           c_func, c_arg,
                                           (long)ts2.tv_sec, ts2.tv_nsec);
                                   }
   #endif
                                   if (!(c_flags & CALLOUT_MPSAFE))
                                           mtx_unlock(&Giant);
                                   mtx_lock_spin(&callout_lock);
                                   steps = 0;
                                   c = nextsoftcheck;
                           }
                   }
           }
           avg_depth += (depth * 1000 - avg_depth) >> 8;
           avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
           avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
           nextsoftcheck = NULL;
           mtx_unlock_spin(&callout_lock);
   }
   
   /*
    * timeout --
    *      Execute a function after a specified length of time.
    *
    * untimeout --
    *      Cancel previous timeout function call.
    *
    * callout_handle_init --
    *      Initialize a handle so that using it with untimeout is benign.
    *
    *      See AT&T BCI Driver Reference Manual for specification.  This
    *      implementation differs from that one in that although an 
    *      identification value is returned from timeout, the original
    *      arguments to timeout as well as the identifier are used to
    *      identify entries for untimeout.
    */
   struct callout_handle
   timeout(ftn, arg, to_ticks)
           timeout_t *ftn;
           void *arg;
           int to_ticks;
   {
           struct callout *new;
           struct callout_handle handle;
   
           mtx_lock_spin(&callout_lock);
   
           /* Fill in the next free callout structure. */
           new = SLIST_FIRST(&callfree);
           if (new == NULL)
                   /* XXX Attempt to malloc first */
                   panic("timeout table full");
           SLIST_REMOVE_HEAD(&callfree, c_links.sle);
           
           callout_reset(new, to_ticks, ftn, arg);
   
           handle.callout = new;
           mtx_unlock_spin(&callout_lock);
           return (handle);
   }
   
   void
   untimeout(ftn, arg, handle)
           timeout_t *ftn;
           void *arg;
           struct callout_handle handle;
   {
   
           /*
            * Check for a handle that was initialized
            * by callout_handle_init, but never used
            * for a real timeout.
            */
           if (handle.callout == NULL)
                   return;
   
           mtx_lock_spin(&callout_lock);
           if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
                   callout_stop(handle.callout);
           mtx_unlock_spin(&callout_lock);
   }
   
   void
   callout_handle_init(struct callout_handle *handle)
   {
           handle->callout = NULL;
   }
   
   /*
    * New interface; clients allocate their own callout structures.
    *
    * callout_reset() - establish or change a timeout
    * callout_stop() - disestablish a timeout
    * callout_init() - initialize a callout structure so that it can
    *      safely be passed to callout_reset() and callout_stop()
    *
    * <sys/callout.h> defines three convenience macros:
    *
    * callout_active() - returns truth if callout has not been serviced
    * callout_pending() - returns truth if callout is still waiting for timeout
    * callout_deactivate() - marks the callout as having been serviced
    */
   void
   callout_reset(c, to_ticks, ftn, arg)
           struct  callout *c;
           int     to_ticks;
           void    (*ftn)(void *);
           void    *arg;
   {
   
           mtx_lock_spin(&callout_lock);
           if (c->c_flags & CALLOUT_PENDING)
                   callout_stop(c);
   
           /*
            * We could unlock callout_lock here and lock it again before the
            * TAILQ_INSERT_TAIL, but there's no point since doing this setup
            * doesn't take much time.
            */
           if (to_ticks <= 0)
                   to_ticks = 1;
   
           c->c_arg = arg;
           c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
           c->c_func = ftn;
           c->c_time = ticks + to_ticks;
           TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
                             c, c_links.tqe);
           mtx_unlock_spin(&callout_lock);
   }
   
   int
   callout_stop(c)
           struct  callout *c;
   {
   
           mtx_lock_spin(&callout_lock);
           /*
            * Don't attempt to delete a callout that's not on the queue.
            */
           if (!(c->c_flags & CALLOUT_PENDING)) {
                   c->c_flags &= ~CALLOUT_ACTIVE;
                   mtx_unlock_spin(&callout_lock);
                   return (0);
           }
           c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
   
           if (nextsoftcheck == c) {
                   nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
           }
           TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
           c->c_func = NULL;
   
           if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
                   SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
           }
           mtx_unlock_spin(&callout_lock);
           return (1);
   }
   
   void
   callout_init(c, mpsafe)
           struct  callout *c;
           int mpsafe;
   {
           bzero(c, sizeof *c);
           if (mpsafe)
                   c->c_flags |= CALLOUT_MPSAFE;
   }
   
   #ifdef APM_FIXUP_CALLTODO
   /* 
    * Adjust the kernel calltodo timeout list.  This routine is used after 
    * an APM resume to recalculate the calltodo timer list values with the 
    * number of hz's we have been sleeping.  The next hardclock() will detect 
    * that there are fired timers and run softclock() to execute them.
    *
    * Please note, I have not done an exhaustive analysis of what code this
    * might break.  I am motivated to have my select()'s and alarm()'s that
    * have expired during suspend firing upon resume so that the applications
    * which set the timer can do the maintanence the timer was for as close
    * as possible to the originally intended time.  Testing this code for a 
    * week showed that resuming from a suspend resulted in 22 to 25 timers 
    * firing, which seemed independant on whether the suspend was 2 hours or
    * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
    */
   void
   adjust_timeout_calltodo(time_change)
       struct timeval *time_change;
   {
           register struct callout *p;
           unsigned long delta_ticks;
   
           /* 
            * How many ticks were we asleep?
            * (stolen from tvtohz()).
            */
   
           /* Don't do anything */
           if (time_change->tv_sec < 0)
                   return;
           else if (time_change->tv_sec <= LONG_MAX / 1000000)
                   delta_ticks = (time_change->tv_sec * 1000000 +
                                  time_change->tv_usec + (tick - 1)) / tick + 1;
           else if (time_change->tv_sec <= LONG_MAX / hz)
                   delta_ticks = time_change->tv_sec * hz +
                                 (time_change->tv_usec + (tick - 1)) / tick + 1;
           else
                   delta_ticks = LONG_MAX;
   
           if (delta_ticks > INT_MAX)
                   delta_ticks = INT_MAX;
   
           /* 
            * Now rip through the timer calltodo list looking for timers
            * to expire.
            */
   
           /* don't collide with softclock() */
           mtx_lock_spin(&callout_lock);
           for (p = calltodo.c_next; p != NULL; p = p->c_next) {
                   p->c_time -= delta_ticks;
   
                   /* Break if the timer had more time on it than delta_ticks */
                   if (p->c_time > 0)
                           break;
   
                   /* take back the ticks the timer didn't use (p->c_time <= 0) */
                   delta_ticks = -p->c_time;
           }
           mtx_unlock_spin(&callout_lock);
   
           return;
   }
   #endif /* APM_FIXUP_CALLTODO */

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