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/9.2/sys/kern/kern_timeout.c 249132 2013-04-05 08:22:11Z mav $");
   39 
   40 #include "opt_kdtrace.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/bus.h>
   45 #include <sys/callout.h>
   46 #include <sys/condvar.h>
   47 #include <sys/interrupt.h>
   48 #include <sys/kernel.h>
   49 #include <sys/ktr.h>
   50 #include <sys/lock.h>
   51 #include <sys/malloc.h>
   52 #include <sys/mutex.h>
   53 #include <sys/proc.h>
   54 #include <sys/sdt.h>
   55 #include <sys/sleepqueue.h>
   56 #include <sys/sysctl.h>
   57 #include <sys/smp.h>
   58 
   59 #ifdef SMP
   60 #include <machine/cpu.h>
   61 #endif
   62 
   63 SDT_PROVIDER_DEFINE(callout_execute);
   64 SDT_PROBE_DEFINE(callout_execute, kernel, , callout_start, callout-start);
   65 SDT_PROBE_ARGTYPE(callout_execute, kernel, , callout_start, 0,
   66     "struct callout *");
   67 SDT_PROBE_DEFINE(callout_execute, kernel, , callout_end, callout-end); 
   68 SDT_PROBE_ARGTYPE(callout_execute, kernel, , callout_end, 0,
   69     "struct callout *");
   70 
   71 static int avg_depth;
   72 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
   73     "Average number of items examined per softclock call. Units = 1/1000");
   74 static int avg_gcalls;
   75 SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
   76     "Average number of Giant callouts made per softclock call. Units = 1/1000");
   77 static int avg_lockcalls;
   78 SYSCTL_INT(_debug, OID_AUTO, to_avg_lockcalls, CTLFLAG_RD, &avg_lockcalls, 0,
   79     "Average number of lock callouts made per softclock call. Units = 1/1000");
   80 static int avg_mpcalls;
   81 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
   82     "Average number of MP callouts made per softclock call. Units = 1/1000");
   83 /*
   84  * TODO:
   85  *      allocate more timeout table slots when table overflows.
   86  */
   87 int callwheelsize, callwheelbits, callwheelmask;
   88 
   89 /*
   90  * The callout cpu migration entity represents informations necessary for
   91  * describing the migrating callout to the new callout cpu.
   92  * The cached informations are very important for deferring migration when
   93  * the migrating callout is already running.
   94  */
   95 struct cc_mig_ent {
   96 #ifdef SMP
   97         void    (*ce_migration_func)(void *);
   98         void    *ce_migration_arg;
   99         int     ce_migration_cpu;
  100         int     ce_migration_ticks;
  101 #endif
  102 };
  103         
  104 /*
  105  * There is one struct callout_cpu per cpu, holding all relevant
  106  * state for the callout processing thread on the individual CPU.
  107  * In particular:
  108  *      cc_ticks is incremented once per tick in callout_cpu().
  109  *      It tracks the global 'ticks' but in a way that the individual
  110  *      threads should not worry about races in the order in which
  111  *      hardclock() and hardclock_cpu() run on the various CPUs.
  112  *      cc_softclock is advanced in callout_cpu() to point to the
  113  *      first entry in cc_callwheel that may need handling. In turn,
  114  *      a softclock() is scheduled so it can serve the various entries i
  115  *      such that cc_softclock <= i <= cc_ticks .
  116  *      XXX maybe cc_softclock and cc_ticks should be volatile ?
  117  *
  118  *      cc_ticks is also used in callout_reset_cpu() to determine
  119  *      when the callout should be served.
  120  */
  121 struct callout_cpu {
  122         struct cc_mig_ent       cc_migrating_entity;
  123         struct mtx              cc_lock;
  124         struct callout          *cc_callout;
  125         struct callout_tailq    *cc_callwheel;
  126         struct callout_list     cc_callfree;
  127         struct callout          *cc_next;
  128         struct callout          *cc_curr;
  129         void                    *cc_cookie;
  130         int                     cc_ticks;
  131         int                     cc_softticks;
  132         int                     cc_cancel;
  133         int                     cc_waiting;
  134         int                     cc_firsttick;
  135 };
  136 
  137 #ifdef SMP
  138 #define cc_migration_func       cc_migrating_entity.ce_migration_func
  139 #define cc_migration_arg        cc_migrating_entity.ce_migration_arg
  140 #define cc_migration_cpu        cc_migrating_entity.ce_migration_cpu
  141 #define cc_migration_ticks      cc_migrating_entity.ce_migration_ticks
  142 
  143 struct callout_cpu cc_cpu[MAXCPU];
  144 #define CPUBLOCK        MAXCPU
  145 #define CC_CPU(cpu)     (&cc_cpu[(cpu)])
  146 #define CC_SELF()       CC_CPU(PCPU_GET(cpuid))
  147 #else
  148 struct callout_cpu cc_cpu;
  149 #define CC_CPU(cpu)     &cc_cpu
  150 #define CC_SELF()       &cc_cpu
  151 #endif
  152 #define CC_LOCK(cc)     mtx_lock_spin(&(cc)->cc_lock)
  153 #define CC_UNLOCK(cc)   mtx_unlock_spin(&(cc)->cc_lock)
  154 #define CC_LOCK_ASSERT(cc)      mtx_assert(&(cc)->cc_lock, MA_OWNED)
  155 
  156 static int timeout_cpu;
  157 void (*callout_new_inserted)(int cpu, int ticks) = NULL;
  158 
  159 static MALLOC_DEFINE(M_CALLOUT, "callout", "Callout datastructures");
  160 
  161 /**
  162  * Locked by cc_lock:
  163  *   cc_curr         - If a callout is in progress, it is curr_callout.
  164  *                     If curr_callout is non-NULL, threads waiting in
  165  *                     callout_drain() will be woken up as soon as the
  166  *                     relevant callout completes.
  167  *   cc_cancel       - Changing to 1 with both callout_lock and c_lock held
  168  *                     guarantees that the current callout will not run.
  169  *                     The softclock() function sets this to 0 before it
  170  *                     drops callout_lock to acquire c_lock, and it calls
  171  *                     the handler only if curr_cancelled is still 0 after
  172  *                     c_lock is successfully acquired.
  173  *   cc_waiting      - If a thread is waiting in callout_drain(), then
  174  *                     callout_wait is nonzero.  Set only when
  175  *                     curr_callout is non-NULL.
  176  */
  177 
  178 /*
  179  * Resets the migration entity tied to a specific callout cpu.
  180  */
  181 static void
  182 cc_cme_cleanup(struct callout_cpu *cc)
  183 {
  184 
  185 #ifdef SMP
  186         cc->cc_migration_cpu = CPUBLOCK;
  187         cc->cc_migration_ticks = 0;
  188         cc->cc_migration_func = NULL;
  189         cc->cc_migration_arg = NULL;
  190 #endif
  191 }
  192 
  193 /*
  194  * Checks if migration is requested by a specific callout cpu.
  195  */
  196 static int
  197 cc_cme_migrating(struct callout_cpu *cc)
  198 {
  199 
  200 #ifdef SMP
  201         return (cc->cc_migration_cpu != CPUBLOCK);
  202 #else
  203         return (0);
  204 #endif
  205 }
  206 
  207 /*
  208  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  209  *
  210  *      This code is called very early in the kernel initialization sequence,
  211  *      and may be called more then once.
  212  */
  213 caddr_t
  214 kern_timeout_callwheel_alloc(caddr_t v)
  215 {
  216         struct callout_cpu *cc;
  217 
  218         timeout_cpu = PCPU_GET(cpuid);
  219         cc = CC_CPU(timeout_cpu);
  220         /*
  221          * Calculate callout wheel size
  222          */
  223         for (callwheelsize = 1, callwheelbits = 0;
  224              callwheelsize < ncallout;
  225              callwheelsize <<= 1, ++callwheelbits)
  226                 ;
  227         callwheelmask = callwheelsize - 1;
  228 
  229         cc->cc_callout = (struct callout *)v;
  230         v = (caddr_t)(cc->cc_callout + ncallout);
  231         cc->cc_callwheel = (struct callout_tailq *)v;
  232         v = (caddr_t)(cc->cc_callwheel + callwheelsize);
  233         return(v);
  234 }
  235 
  236 static void
  237 callout_cpu_init(struct callout_cpu *cc)
  238 {
  239         struct callout *c;
  240         int i;
  241 
  242         mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  243         SLIST_INIT(&cc->cc_callfree);
  244         for (i = 0; i < callwheelsize; i++) {
  245                 TAILQ_INIT(&cc->cc_callwheel[i]);
  246         }
  247         cc_cme_cleanup(cc);
  248         if (cc->cc_callout == NULL)
  249                 return;
  250         for (i = 0; i < ncallout; i++) {
  251                 c = &cc->cc_callout[i];
  252                 callout_init(c, 0);
  253                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  254                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  255         }
  256 }
  257 
  258 #ifdef SMP
  259 /*
  260  * Switches the cpu tied to a specific callout.
  261  * The function expects a locked incoming callout cpu and returns with
  262  * locked outcoming callout cpu.
  263  */
  264 static struct callout_cpu *
  265 callout_cpu_switch(struct callout *c, struct callout_cpu *cc, int new_cpu)
  266 {
  267         struct callout_cpu *new_cc;
  268 
  269         MPASS(c != NULL && cc != NULL);
  270         CC_LOCK_ASSERT(cc);
  271 
  272         /*
  273          * Avoid interrupts and preemption firing after the callout cpu
  274          * is blocked in order to avoid deadlocks as the new thread
  275          * may be willing to acquire the callout cpu lock.
  276          */
  277         c->c_cpu = CPUBLOCK;
  278         spinlock_enter();
  279         CC_UNLOCK(cc);
  280         new_cc = CC_CPU(new_cpu);
  281         CC_LOCK(new_cc);
  282         spinlock_exit();
  283         c->c_cpu = new_cpu;
  284         return (new_cc);
  285 }
  286 #endif
  287 
  288 /*
  289  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  290  *                                 space.
  291  *
  292  *      This code is called just once, after the space reserved for the
  293  *      callout wheel has been finalized.
  294  */
  295 void
  296 kern_timeout_callwheel_init(void)
  297 {
  298         callout_cpu_init(CC_CPU(timeout_cpu));
  299 }
  300 
  301 /*
  302  * Start standard softclock thread.
  303  */
  304 static void
  305 start_softclock(void *dummy)
  306 {
  307         struct callout_cpu *cc;
  308 #ifdef SMP
  309         int cpu;
  310 #endif
  311 
  312         cc = CC_CPU(timeout_cpu);
  313         if (swi_add(&clk_intr_event, "clock", softclock, cc, SWI_CLOCK,
  314             INTR_MPSAFE, &cc->cc_cookie))
  315                 panic("died while creating standard software ithreads");
  316 #ifdef SMP
  317         CPU_FOREACH(cpu) {
  318                 if (cpu == timeout_cpu)
  319                         continue;
  320                 cc = CC_CPU(cpu);
  321                 if (swi_add(NULL, "clock", softclock, cc, SWI_CLOCK,
  322                     INTR_MPSAFE, &cc->cc_cookie))
  323                         panic("died while creating standard software ithreads");
  324                 cc->cc_callout = NULL;  /* Only cpu0 handles timeout(). */
  325                 cc->cc_callwheel = malloc(
  326                     sizeof(struct callout_tailq) * callwheelsize, M_CALLOUT,
  327                     M_WAITOK);
  328                 callout_cpu_init(cc);
  329         }
  330 #endif
  331 }
  332 
  333 SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);
  334 
  335 void
  336 callout_tick(void)
  337 {
  338         struct callout_cpu *cc;
  339         int need_softclock;
  340         int bucket;
  341 
  342         /*
  343          * Process callouts at a very low cpu priority, so we don't keep the
  344          * relatively high clock interrupt priority any longer than necessary.
  345          */
  346         need_softclock = 0;
  347         cc = CC_SELF();
  348         mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
  349         cc->cc_firsttick = cc->cc_ticks = ticks;
  350         for (; (cc->cc_softticks - cc->cc_ticks) <= 0; cc->cc_softticks++) {
  351                 bucket = cc->cc_softticks & callwheelmask;
  352                 if (!TAILQ_EMPTY(&cc->cc_callwheel[bucket])) {
  353                         need_softclock = 1;
  354                         break;
  355                 }
  356         }
  357         mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
  358         /*
  359          * swi_sched acquires the thread lock, so we don't want to call it
  360          * with cc_lock held; incorrect locking order.
  361          */
  362         if (need_softclock)
  363                 swi_sched(cc->cc_cookie, 0);
  364 }
  365 
  366 int
  367 callout_tickstofirst(int limit)
  368 {
  369         struct callout_cpu *cc;
  370         struct callout *c;
  371         struct callout_tailq *sc;
  372         int curticks;
  373         int skip = 1;
  374 
  375         cc = CC_SELF();
  376         mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
  377         curticks = cc->cc_ticks;
  378         while( skip < ncallout && skip < limit ) {
  379                 sc = &cc->cc_callwheel[ (curticks+skip) & callwheelmask ];
  380                 /* search scanning ticks */
  381                 TAILQ_FOREACH( c, sc, c_links.tqe ){
  382                         if (c->c_time - curticks <= ncallout)
  383                                 goto out;
  384                 }
  385                 skip++;
  386         }
  387 out:
  388         cc->cc_firsttick = curticks + skip;
  389         mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
  390         return (skip);
  391 }
  392 
  393 static struct callout_cpu *
  394 callout_lock(struct callout *c)
  395 {
  396         struct callout_cpu *cc;
  397         int cpu;
  398 
  399         for (;;) {
  400                 cpu = c->c_cpu;
  401 #ifdef SMP
  402                 if (cpu == CPUBLOCK) {
  403                         while (c->c_cpu == CPUBLOCK)
  404                                 cpu_spinwait();
  405                         continue;
  406                 }
  407 #endif
  408                 cc = CC_CPU(cpu);
  409                 CC_LOCK(cc);
  410                 if (cpu == c->c_cpu)
  411                         break;
  412                 CC_UNLOCK(cc);
  413         }
  414         return (cc);
  415 }
  416 
  417 static void
  418 callout_cc_add(struct callout *c, struct callout_cpu *cc, int to_ticks,
  419     void (*func)(void *), void *arg, int cpu)
  420 {
  421 
  422         CC_LOCK_ASSERT(cc);
  423 
  424         if (to_ticks <= 0)
  425                 to_ticks = 1;
  426         c->c_arg = arg;
  427         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  428         c->c_func = func;
  429         c->c_time = ticks + to_ticks;
  430         TAILQ_INSERT_TAIL(&cc->cc_callwheel[c->c_time & callwheelmask], 
  431             c, c_links.tqe);
  432         if ((c->c_time - cc->cc_firsttick) < 0 &&
  433             callout_new_inserted != NULL) {
  434                 cc->cc_firsttick = c->c_time;
  435                 (*callout_new_inserted)(cpu,
  436                     to_ticks + (ticks - cc->cc_ticks));
  437         }
  438 }
  439 
  440 static void
  441 callout_cc_del(struct callout *c, struct callout_cpu *cc)
  442 {
  443 
  444         if ((c->c_flags & CALLOUT_LOCAL_ALLOC) == 0)
  445                 return;
  446         c->c_func = NULL;
  447         SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  448 }
  449 
  450 static void
  451 softclock_call_cc(struct callout *c, struct callout_cpu *cc, int *mpcalls,
  452     int *lockcalls, int *gcalls)
  453 {
  454         void (*c_func)(void *);
  455         void *c_arg;
  456         struct lock_class *class;
  457         struct lock_object *c_lock;
  458         int c_flags, sharedlock;
  459 #ifdef SMP
  460         struct callout_cpu *new_cc;
  461         void (*new_func)(void *);
  462         void *new_arg;
  463         int new_cpu, new_ticks;
  464 #endif
  465 #ifdef DIAGNOSTIC
  466         struct bintime bt1, bt2;
  467         struct timespec ts2;
  468         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  469         static timeout_t *lastfunc;
  470 #endif
  471 
  472         KASSERT((c->c_flags & (CALLOUT_PENDING | CALLOUT_ACTIVE)) ==
  473             (CALLOUT_PENDING | CALLOUT_ACTIVE),
  474             ("softclock_call_cc: pend|act %p %x", c, c->c_flags));
  475         class = (c->c_lock != NULL) ? LOCK_CLASS(c->c_lock) : NULL;
  476         sharedlock = (c->c_flags & CALLOUT_SHAREDLOCK) ? 0 : 1;
  477         c_lock = c->c_lock;
  478         c_func = c->c_func;
  479         c_arg = c->c_arg;
  480         c_flags = c->c_flags;
  481         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  482                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  483         else
  484                 c->c_flags &= ~CALLOUT_PENDING;
  485         cc->cc_curr = c;
  486         cc->cc_cancel = 0;
  487         CC_UNLOCK(cc);
  488         if (c_lock != NULL) {
  489                 class->lc_lock(c_lock, sharedlock);
  490                 /*
  491                  * The callout may have been cancelled
  492                  * while we switched locks.
  493                  */
  494                 if (cc->cc_cancel) {
  495                         class->lc_unlock(c_lock);
  496                         goto skip;
  497                 }
  498                 /* The callout cannot be stopped now. */
  499                 cc->cc_cancel = 1;
  500 
  501                 if (c_lock == &Giant.lock_object) {
  502                         (*gcalls)++;
  503                         CTR3(KTR_CALLOUT, "callout %p func %p arg %p",
  504                             c, c_func, c_arg);
  505                 } else {
  506                         (*lockcalls)++;
  507                         CTR3(KTR_CALLOUT, "callout lock %p func %p arg %p",
  508                             c, c_func, c_arg);
  509                 }
  510         } else {
  511                 (*mpcalls)++;
  512                 CTR3(KTR_CALLOUT, "callout mpsafe %p func %p arg %p",
  513                     c, c_func, c_arg);
  514         }
  515 #ifdef DIAGNOSTIC
  516         binuptime(&bt1);
  517 #endif
  518         THREAD_NO_SLEEPING();
  519         SDT_PROBE(callout_execute, kernel, , callout_start, c, 0, 0, 0, 0);
  520         c_func(c_arg);
  521         SDT_PROBE(callout_execute, kernel, , callout_end, c, 0, 0, 0, 0);
  522         THREAD_SLEEPING_OK();
  523 #ifdef DIAGNOSTIC
  524         binuptime(&bt2);
  525         bintime_sub(&bt2, &bt1);
  526         if (bt2.frac > maxdt) {
  527                 if (lastfunc != c_func || bt2.frac > maxdt * 2) {
  528                         bintime2timespec(&bt2, &ts2);
  529                         printf(
  530                 "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  531                             c_func, c_arg, (intmax_t)ts2.tv_sec, ts2.tv_nsec);
  532                 }
  533                 maxdt = bt2.frac;
  534                 lastfunc = c_func;
  535         }
  536 #endif
  537         CTR1(KTR_CALLOUT, "callout %p finished", c);
  538         if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
  539                 class->lc_unlock(c_lock);
  540 skip:
  541         CC_LOCK(cc);
  542         KASSERT(cc->cc_curr == c, ("mishandled cc_curr"));
  543         cc->cc_curr = NULL;
  544         if (cc->cc_waiting) {
  545                 /*
  546                  * There is someone waiting for the
  547                  * callout to complete.
  548                  * If the callout was scheduled for
  549                  * migration just cancel it.
  550                  */
  551                 if (cc_cme_migrating(cc)) {
  552                         cc_cme_cleanup(cc);
  553 
  554                         /*
  555                          * It should be assert here that the callout is not
  556                          * destroyed but that is not easy.
  557                          */
  558                         c->c_flags &= ~CALLOUT_DFRMIGRATION;
  559                 }
  560                 cc->cc_waiting = 0;
  561                 CC_UNLOCK(cc);
  562                 wakeup(&cc->cc_waiting);
  563                 CC_LOCK(cc);
  564         } else if (cc_cme_migrating(cc)) {
  565                 KASSERT((c_flags & CALLOUT_LOCAL_ALLOC) == 0,
  566                     ("Migrating legacy callout %p", c));
  567 #ifdef SMP
  568                 /*
  569                  * If the callout was scheduled for
  570                  * migration just perform it now.
  571                  */
  572                 new_cpu = cc->cc_migration_cpu;
  573                 new_ticks = cc->cc_migration_ticks;
  574                 new_func = cc->cc_migration_func;
  575                 new_arg = cc->cc_migration_arg;
  576                 cc_cme_cleanup(cc);
  577 
  578                 /*
  579                  * It should be assert here that the callout is not destroyed
  580                  * but that is not easy.
  581                  *
  582                  * As first thing, handle deferred callout stops.
  583                  */
  584                 if ((c->c_flags & CALLOUT_DFRMIGRATION) == 0) {
  585                         CTR3(KTR_CALLOUT,
  586                              "deferred cancelled %p func %p arg %p",
  587                              c, new_func, new_arg);
  588                         callout_cc_del(c, cc);
  589                         return;
  590                 }
  591                 c->c_flags &= ~CALLOUT_DFRMIGRATION;
  592 
  593                 new_cc = callout_cpu_switch(c, cc, new_cpu);
  594                 callout_cc_add(c, new_cc, new_ticks, new_func, new_arg,
  595                     new_cpu);
  596                 CC_UNLOCK(new_cc);
  597                 CC_LOCK(cc);
  598 #else
  599                 panic("migration should not happen");
  600 #endif
  601         }
  602         /*
  603          * If the current callout is locally allocated (from
  604          * timeout(9)) then put it on the freelist.
  605          *
  606          * Note: we need to check the cached copy of c_flags because
  607          * if it was not local, then it's not safe to deref the
  608          * callout pointer.
  609          */
  610         KASSERT((c_flags & CALLOUT_LOCAL_ALLOC) == 0 ||
  611             c->c_flags == CALLOUT_LOCAL_ALLOC,
  612             ("corrupted callout"));
  613         if (c_flags & CALLOUT_LOCAL_ALLOC)
  614                 callout_cc_del(c, cc);
  615 }
  616 
  617 /*
  618  * The callout mechanism is based on the work of Adam M. Costello and 
  619  * George Varghese, published in a technical report entitled "Redesigning
  620  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  621  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  622  * used in this implementation was published by G. Varghese and T. Lauck in
  623  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  624  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  625  * the 11th ACM Annual Symposium on Operating Systems Principles,
  626  * Austin, Texas Nov 1987.
  627  */
  628 
  629 /*
  630  * Software (low priority) clock interrupt.
  631  * Run periodic events from timeout queue.
  632  */
  633 void
  634 softclock(void *arg)
  635 {
  636         struct callout_cpu *cc;
  637         struct callout *c;
  638         struct callout_tailq *bucket;
  639         int curticks;
  640         int steps;      /* #steps since we last allowed interrupts */
  641         int depth;
  642         int mpcalls;
  643         int lockcalls;
  644         int gcalls;
  645 
  646 #ifndef MAX_SOFTCLOCK_STEPS
  647 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  648 #endif /* MAX_SOFTCLOCK_STEPS */
  649 
  650         mpcalls = 0;
  651         lockcalls = 0;
  652         gcalls = 0;
  653         depth = 0;
  654         steps = 0;
  655         cc = (struct callout_cpu *)arg;
  656         CC_LOCK(cc);
  657         while (cc->cc_softticks - 1 != cc->cc_ticks) {
  658                 /*
  659                  * cc_softticks may be modified by hard clock, so cache
  660                  * it while we work on a given bucket.
  661                  */
  662                 curticks = cc->cc_softticks;
  663                 cc->cc_softticks++;
  664                 bucket = &cc->cc_callwheel[curticks & callwheelmask];
  665                 c = TAILQ_FIRST(bucket);
  666                 while (c != NULL) {
  667                         depth++;
  668                         if (c->c_time != curticks) {
  669                                 c = TAILQ_NEXT(c, c_links.tqe);
  670                                 ++steps;
  671                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  672                                         cc->cc_next = c;
  673                                         /* Give interrupts a chance. */
  674                                         CC_UNLOCK(cc);
  675                                         ;       /* nothing */
  676                                         CC_LOCK(cc);
  677                                         c = cc->cc_next;
  678                                         steps = 0;
  679                                 }
  680                         } else {
  681                                 cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  682                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  683                                 softclock_call_cc(c, cc, &mpcalls,
  684                                     &lockcalls, &gcalls);
  685                                 steps = 0;
  686                                 c = cc->cc_next;
  687                         }
  688                 }
  689         }
  690         avg_depth += (depth * 1000 - avg_depth) >> 8;
  691         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  692         avg_lockcalls += (lockcalls * 1000 - avg_lockcalls) >> 8;
  693         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  694         cc->cc_next = NULL;
  695         CC_UNLOCK(cc);
  696 }
  697 
  698 /*
  699  * timeout --
  700  *      Execute a function after a specified length of time.
  701  *
  702  * untimeout --
  703  *      Cancel previous timeout function call.
  704  *
  705  * callout_handle_init --
  706  *      Initialize a handle so that using it with untimeout is benign.
  707  *
  708  *      See AT&T BCI Driver Reference Manual for specification.  This
  709  *      implementation differs from that one in that although an 
  710  *      identification value is returned from timeout, the original
  711  *      arguments to timeout as well as the identifier are used to
  712  *      identify entries for untimeout.
  713  */
  714 struct callout_handle
  715 timeout(ftn, arg, to_ticks)
  716         timeout_t *ftn;
  717         void *arg;
  718         int to_ticks;
  719 {
  720         struct callout_cpu *cc;
  721         struct callout *new;
  722         struct callout_handle handle;
  723 
  724         cc = CC_CPU(timeout_cpu);
  725         CC_LOCK(cc);
  726         /* Fill in the next free callout structure. */
  727         new = SLIST_FIRST(&cc->cc_callfree);
  728         if (new == NULL)
  729                 /* XXX Attempt to malloc first */
  730                 panic("timeout table full");
  731         SLIST_REMOVE_HEAD(&cc->cc_callfree, c_links.sle);
  732         callout_reset(new, to_ticks, ftn, arg);
  733         handle.callout = new;
  734         CC_UNLOCK(cc);
  735 
  736         return (handle);
  737 }
  738 
  739 void
  740 untimeout(ftn, arg, handle)
  741         timeout_t *ftn;
  742         void *arg;
  743         struct callout_handle handle;
  744 {
  745         struct callout_cpu *cc;
  746 
  747         /*
  748          * Check for a handle that was initialized
  749          * by callout_handle_init, but never used
  750          * for a real timeout.
  751          */
  752         if (handle.callout == NULL)
  753                 return;
  754 
  755         cc = callout_lock(handle.callout);
  756         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  757                 callout_stop(handle.callout);
  758         CC_UNLOCK(cc);
  759 }
  760 
  761 void
  762 callout_handle_init(struct callout_handle *handle)
  763 {
  764         handle->callout = NULL;
  765 }
  766 
  767 /*
  768  * New interface; clients allocate their own callout structures.
  769  *
  770  * callout_reset() - establish or change a timeout
  771  * callout_stop() - disestablish a timeout
  772  * callout_init() - initialize a callout structure so that it can
  773  *      safely be passed to callout_reset() and callout_stop()
  774  *
  775  * <sys/callout.h> defines three convenience macros:
  776  *
  777  * callout_active() - returns truth if callout has not been stopped,
  778  *      drained, or deactivated since the last time the callout was
  779  *      reset.
  780  * callout_pending() - returns truth if callout is still waiting for timeout
  781  * callout_deactivate() - marks the callout as having been serviced
  782  */
  783 int
  784 callout_reset_on(struct callout *c, int to_ticks, void (*ftn)(void *),
  785     void *arg, int cpu)
  786 {
  787         struct callout_cpu *cc;
  788         int cancelled = 0;
  789 
  790         /*
  791          * Don't allow migration of pre-allocated callouts lest they
  792          * become unbalanced.
  793          */
  794         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  795                 cpu = c->c_cpu;
  796         cc = callout_lock(c);
  797         if (cc->cc_curr == c) {
  798                 /*
  799                  * We're being asked to reschedule a callout which is
  800                  * currently in progress.  If there is a lock then we
  801                  * can cancel the callout if it has not really started.
  802                  */
  803                 if (c->c_lock != NULL && !cc->cc_cancel)
  804                         cancelled = cc->cc_cancel = 1;
  805                 if (cc->cc_waiting) {
  806                         /*
  807                          * Someone has called callout_drain to kill this
  808                          * callout.  Don't reschedule.
  809                          */
  810                         CTR4(KTR_CALLOUT, "%s %p func %p arg %p",
  811                             cancelled ? "cancelled" : "failed to cancel",
  812                             c, c->c_func, c->c_arg);
  813                         CC_UNLOCK(cc);
  814                         return (cancelled);
  815                 }
  816         }
  817         if (c->c_flags & CALLOUT_PENDING) {
  818                 if (cc->cc_next == c) {
  819                         cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  820                 }
  821                 TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], c,
  822                     c_links.tqe);
  823 
  824                 cancelled = 1;
  825                 c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  826         }
  827 
  828 #ifdef SMP
  829         /*
  830          * If the callout must migrate try to perform it immediately.
  831          * If the callout is currently running, just defer the migration
  832          * to a more appropriate moment.
  833          */
  834         if (c->c_cpu != cpu) {
  835                 if (cc->cc_curr == c) {
  836                         cc->cc_migration_cpu = cpu;
  837                         cc->cc_migration_ticks = to_ticks;
  838                         cc->cc_migration_func = ftn;
  839                         cc->cc_migration_arg = arg;
  840                         c->c_flags |= CALLOUT_DFRMIGRATION;
  841                         CTR5(KTR_CALLOUT,
  842                     "migration of %p func %p arg %p in %d to %u deferred",
  843                             c, c->c_func, c->c_arg, to_ticks, cpu);
  844                         CC_UNLOCK(cc);
  845                         return (cancelled);
  846                 }
  847                 cc = callout_cpu_switch(c, cc, cpu);
  848         }
  849 #endif
  850 
  851         callout_cc_add(c, cc, to_ticks, ftn, arg, cpu);
  852         CTR5(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d",
  853             cancelled ? "re" : "", c, c->c_func, c->c_arg, to_ticks);
  854         CC_UNLOCK(cc);
  855 
  856         return (cancelled);
  857 }
  858 
  859 /*
  860  * Common idioms that can be optimized in the future.
  861  */
  862 int
  863 callout_schedule_on(struct callout *c, int to_ticks, int cpu)
  864 {
  865         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, cpu);
  866 }
  867 
  868 int
  869 callout_schedule(struct callout *c, int to_ticks)
  870 {
  871         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, c->c_cpu);
  872 }
  873 
  874 int
  875 _callout_stop_safe(c, safe)
  876         struct  callout *c;
  877         int     safe;
  878 {
  879         struct callout_cpu *cc, *old_cc;
  880         struct lock_class *class;
  881         int use_lock, sq_locked;
  882 
  883         /*
  884          * Some old subsystems don't hold Giant while running a callout_stop(),
  885          * so just discard this check for the moment.
  886          */
  887         if (!safe && c->c_lock != NULL) {
  888                 if (c->c_lock == &Giant.lock_object)
  889                         use_lock = mtx_owned(&Giant);
  890                 else {
  891                         use_lock = 1;
  892                         class = LOCK_CLASS(c->c_lock);
  893                         class->lc_assert(c->c_lock, LA_XLOCKED);
  894                 }
  895         } else
  896                 use_lock = 0;
  897 
  898         sq_locked = 0;
  899         old_cc = NULL;
  900 again:
  901         cc = callout_lock(c);
  902 
  903         /*
  904          * If the callout was migrating while the callout cpu lock was
  905          * dropped,  just drop the sleepqueue lock and check the states
  906          * again.
  907          */
  908         if (sq_locked != 0 && cc != old_cc) {
  909 #ifdef SMP
  910                 CC_UNLOCK(cc);
  911                 sleepq_release(&old_cc->cc_waiting);
  912                 sq_locked = 0;
  913                 old_cc = NULL;
  914                 goto again;
  915 #else
  916                 panic("migration should not happen");
  917 #endif
  918         }
  919 
  920         /*
  921          * If the callout isn't pending, it's not on the queue, so
  922          * don't attempt to remove it from the queue.  We can try to
  923          * stop it by other means however.
  924          */
  925         if (!(c->c_flags & CALLOUT_PENDING)) {
  926                 c->c_flags &= ~CALLOUT_ACTIVE;
  927 
  928                 /*
  929                  * If it wasn't on the queue and it isn't the current
  930                  * callout, then we can't stop it, so just bail.
  931                  */
  932                 if (cc->cc_curr != c) {
  933                         CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  934                             c, c->c_func, c->c_arg);
  935                         CC_UNLOCK(cc);
  936                         if (sq_locked)
  937                                 sleepq_release(&cc->cc_waiting);
  938                         return (0);
  939                 }
  940 
  941                 if (safe) {
  942                         /*
  943                          * The current callout is running (or just
  944                          * about to run) and blocking is allowed, so
  945                          * just wait for the current invocation to
  946                          * finish.
  947                          */
  948                         while (cc->cc_curr == c) {
  949 
  950                                 /*
  951                                  * Use direct calls to sleepqueue interface
  952                                  * instead of cv/msleep in order to avoid
  953                                  * a LOR between cc_lock and sleepqueue
  954                                  * chain spinlocks.  This piece of code
  955                                  * emulates a msleep_spin() call actually.
  956                                  *
  957                                  * If we already have the sleepqueue chain
  958                                  * locked, then we can safely block.  If we
  959                                  * don't already have it locked, however,
  960                                  * we have to drop the cc_lock to lock
  961                                  * it.  This opens several races, so we
  962                                  * restart at the beginning once we have
  963                                  * both locks.  If nothing has changed, then
  964                                  * we will end up back here with sq_locked
  965                                  * set.
  966                                  */
  967                                 if (!sq_locked) {
  968                                         CC_UNLOCK(cc);
  969                                         sleepq_lock(&cc->cc_waiting);
  970                                         sq_locked = 1;
  971                                         old_cc = cc;
  972                                         goto again;
  973                                 }
  974 
  975                                 /*
  976                                  * Migration could be cancelled here, but
  977                                  * as long as it is still not sure when it
  978                                  * will be packed up, just let softclock()
  979                                  * take care of it.
  980                                  */
  981                                 cc->cc_waiting = 1;
  982                                 DROP_GIANT();
  983                                 CC_UNLOCK(cc);
  984                                 sleepq_add(&cc->cc_waiting,
  985                                     &cc->cc_lock.lock_object, "codrain",
  986                                     SLEEPQ_SLEEP, 0);
  987                                 sleepq_wait(&cc->cc_waiting, 0);
  988                                 sq_locked = 0;
  989                                 old_cc = NULL;
  990 
  991                                 /* Reacquire locks previously released. */
  992                                 PICKUP_GIANT();
  993                                 CC_LOCK(cc);
  994                         }
  995                 } else if (use_lock && !cc->cc_cancel) {
  996                         /*
  997                          * The current callout is waiting for its
  998                          * lock which we hold.  Cancel the callout
  999                          * and return.  After our caller drops the
 1000                          * lock, the callout will be skipped in
 1001                          * softclock().
 1002                          */
 1003                         cc->cc_cancel = 1;
 1004                         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
 1005                             c, c->c_func, c->c_arg);
 1006                         KASSERT(!cc_cme_migrating(cc),
 1007                             ("callout wrongly scheduled for migration"));
 1008                         CC_UNLOCK(cc);
 1009                         KASSERT(!sq_locked, ("sleepqueue chain locked"));
 1010                         return (1);
 1011                 } else if ((c->c_flags & CALLOUT_DFRMIGRATION) != 0) {
 1012                         c->c_flags &= ~CALLOUT_DFRMIGRATION;
 1013                         CTR3(KTR_CALLOUT, "postponing stop %p func %p arg %p",
 1014                             c, c->c_func, c->c_arg);
 1015                         CC_UNLOCK(cc);
 1016                         return (1);
 1017                 }
 1018                 CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
 1019                     c, c->c_func, c->c_arg);
 1020                 CC_UNLOCK(cc);
 1021                 KASSERT(!sq_locked, ("sleepqueue chain still locked"));
 1022                 return (0);
 1023         }
 1024         if (sq_locked)
 1025                 sleepq_release(&cc->cc_waiting);
 1026 
 1027         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
 1028 
 1029         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
 1030             c, c->c_func, c->c_arg);
 1031         if (cc->cc_next == c)
 1032                 cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
 1033         TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], c,
 1034             c_links.tqe);
 1035         callout_cc_del(c, cc);
 1036 
 1037         CC_UNLOCK(cc);
 1038         return (1);
 1039 }
 1040 
 1041 void
 1042 callout_init(c, mpsafe)
 1043         struct  callout *c;
 1044         int mpsafe;
 1045 {
 1046         bzero(c, sizeof *c);
 1047         if (mpsafe) {
 1048                 c->c_lock = NULL;
 1049                 c->c_flags = CALLOUT_RETURNUNLOCKED;
 1050         } else {
 1051                 c->c_lock = &Giant.lock_object;
 1052                 c->c_flags = 0;
 1053         }
 1054         c->c_cpu = timeout_cpu;
 1055 }
 1056 
 1057 void
 1058 _callout_init_lock(c, lock, flags)
 1059         struct  callout *c;
 1060         struct  lock_object *lock;
 1061         int flags;
 1062 {
 1063         bzero(c, sizeof *c);
 1064         c->c_lock = lock;
 1065         KASSERT((flags & ~(CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK)) == 0,
 1066             ("callout_init_lock: bad flags %d", flags));
 1067         KASSERT(lock != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
 1068             ("callout_init_lock: CALLOUT_RETURNUNLOCKED with no lock"));
 1069         KASSERT(lock == NULL || !(LOCK_CLASS(lock)->lc_flags &
 1070             (LC_SPINLOCK | LC_SLEEPABLE)), ("%s: invalid lock class",
 1071             __func__));
 1072         c->c_flags = flags & (CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK);
 1073         c->c_cpu = timeout_cpu;
 1074 }
 1075 
 1076 #ifdef APM_FIXUP_CALLTODO
 1077 /* 
 1078  * Adjust the kernel calltodo timeout list.  This routine is used after 
 1079  * an APM resume to recalculate the calltodo timer list values with the 
 1080  * number of hz's we have been sleeping.  The next hardclock() will detect 
 1081  * that there are fired timers and run softclock() to execute them.
 1082  *
 1083  * Please note, I have not done an exhaustive analysis of what code this
 1084  * might break.  I am motivated to have my select()'s and alarm()'s that
 1085  * have expired during suspend firing upon resume so that the applications
 1086  * which set the timer can do the maintanence the timer was for as close
 1087  * as possible to the originally intended time.  Testing this code for a 
 1088  * week showed that resuming from a suspend resulted in 22 to 25 timers 
 1089  * firing, which seemed independant on whether the suspend was 2 hours or
 1090  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
 1091  */
 1092 void
 1093 adjust_timeout_calltodo(time_change)
 1094     struct timeval *time_change;
 1095 {
 1096         register struct callout *p;
 1097         unsigned long delta_ticks;
 1098 
 1099         /* 
 1100          * How many ticks were we asleep?
 1101          * (stolen from tvtohz()).
 1102          */
 1103 
 1104         /* Don't do anything */
 1105         if (time_change->tv_sec < 0)
 1106                 return;
 1107         else if (time_change->tv_sec <= LONG_MAX / 1000000)
 1108                 delta_ticks = (time_change->tv_sec * 1000000 +
 1109                                time_change->tv_usec + (tick - 1)) / tick + 1;
 1110         else if (time_change->tv_sec <= LONG_MAX / hz)
 1111                 delta_ticks = time_change->tv_sec * hz +
 1112                               (time_change->tv_usec + (tick - 1)) / tick + 1;
 1113         else
 1114                 delta_ticks = LONG_MAX;
 1115 
 1116         if (delta_ticks > INT_MAX)
 1117                 delta_ticks = INT_MAX;
 1118 
 1119         /* 
 1120          * Now rip through the timer calltodo list looking for timers
 1121          * to expire.
 1122          */
 1123 
 1124         /* don't collide with softclock() */
 1125         CC_LOCK(cc);
 1126         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
 1127                 p->c_time -= delta_ticks;
 1128 
 1129                 /* Break if the timer had more time on it than delta_ticks */
 1130                 if (p->c_time > 0)
 1131                         break;
 1132 
 1133                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
 1134                 delta_ticks = -p->c_time;
 1135         }
 1136         CC_UNLOCK(cc);
 1137 
 1138         return;
 1139 }
 1140 #endif /* APM_FIXUP_CALLTODO */

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