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  * 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/8.4/sys/kern/kern_timeout.c 235225 2012-05-10 11:08:09Z kib $");
   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 };
  135 
  136 #ifdef SMP
  137 #define cc_migration_func       cc_migrating_entity.ce_migration_func
  138 #define cc_migration_arg        cc_migrating_entity.ce_migration_arg
  139 #define cc_migration_cpu        cc_migrating_entity.ce_migration_cpu
  140 #define cc_migration_ticks      cc_migrating_entity.ce_migration_ticks
  141 
  142 struct callout_cpu cc_cpu[MAXCPU];
  143 #define CPUBLOCK        MAXCPU
  144 #define CC_CPU(cpu)     (&cc_cpu[(cpu)])
  145 #define CC_SELF()       CC_CPU(PCPU_GET(cpuid))
  146 #else
  147 struct callout_cpu cc_cpu;
  148 #define CC_CPU(cpu)     &cc_cpu
  149 #define CC_SELF()       &cc_cpu
  150 #endif
  151 #define CC_LOCK(cc)     mtx_lock_spin(&(cc)->cc_lock)
  152 #define CC_UNLOCK(cc)   mtx_unlock_spin(&(cc)->cc_lock)
  153 #define CC_LOCK_ASSERT(cc)      mtx_assert(&(cc)->cc_lock, MA_OWNED)
  154 
  155 static int timeout_cpu;
  156 
  157 MALLOC_DEFINE(M_CALLOUT, "callout", "Callout datastructures");
  158 
  159 /**
  160  * Locked by cc_lock:
  161  *   cc_curr         - If a callout is in progress, it is curr_callout.
  162  *                     If curr_callout is non-NULL, threads waiting in
  163  *                     callout_drain() will be woken up as soon as the
  164  *                     relevant callout completes.
  165  *   cc_cancel       - Changing to 1 with both callout_lock and c_lock held
  166  *                     guarantees that the current callout will not run.
  167  *                     The softclock() function sets this to 0 before it
  168  *                     drops callout_lock to acquire c_lock, and it calls
  169  *                     the handler only if curr_cancelled is still 0 after
  170  *                     c_lock is successfully acquired.
  171  *   cc_waiting      - If a thread is waiting in callout_drain(), then
  172  *                     callout_wait is nonzero.  Set only when
  173  *                     curr_callout is non-NULL.
  174  */
  175 
  176 /*
  177  * Resets the migration entity tied to a specific callout cpu.
  178  */
  179 static void
  180 cc_cme_cleanup(struct callout_cpu *cc)
  181 {
  182 
  183 #ifdef SMP
  184         cc->cc_migration_cpu = CPUBLOCK;
  185         cc->cc_migration_ticks = 0;
  186         cc->cc_migration_func = NULL;
  187         cc->cc_migration_arg = NULL;
  188 #endif
  189 }
  190 
  191 /*
  192  * Checks if migration is requested by a specific callout cpu.
  193  */
  194 static int
  195 cc_cme_migrating(struct callout_cpu *cc)
  196 {
  197 
  198 #ifdef SMP
  199         return (cc->cc_migration_cpu != CPUBLOCK);
  200 #else
  201         return (0);
  202 #endif
  203 }
  204 
  205 /*
  206  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  207  *
  208  *      This code is called very early in the kernel initialization sequence,
  209  *      and may be called more then once.
  210  */
  211 caddr_t
  212 kern_timeout_callwheel_alloc(caddr_t v)
  213 {
  214         struct callout_cpu *cc;
  215 
  216         timeout_cpu = PCPU_GET(cpuid);
  217         cc = CC_CPU(timeout_cpu);
  218         /*
  219          * Calculate callout wheel size
  220          */
  221         for (callwheelsize = 1, callwheelbits = 0;
  222              callwheelsize < ncallout;
  223              callwheelsize <<= 1, ++callwheelbits)
  224                 ;
  225         callwheelmask = callwheelsize - 1;
  226 
  227         cc->cc_callout = (struct callout *)v;
  228         v = (caddr_t)(cc->cc_callout + ncallout);
  229         cc->cc_callwheel = (struct callout_tailq *)v;
  230         v = (caddr_t)(cc->cc_callwheel + callwheelsize);
  231         return(v);
  232 }
  233 
  234 static void
  235 callout_cpu_init(struct callout_cpu *cc)
  236 {
  237         struct callout *c;
  238         int i;
  239 
  240         mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  241         SLIST_INIT(&cc->cc_callfree);
  242         for (i = 0; i < callwheelsize; i++) {
  243                 TAILQ_INIT(&cc->cc_callwheel[i]);
  244         }
  245         cc_cme_cleanup(cc);
  246         if (cc->cc_callout == NULL)
  247                 return;
  248         for (i = 0; i < ncallout; i++) {
  249                 c = &cc->cc_callout[i];
  250                 callout_init(c, 0);
  251                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  252                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  253         }
  254 }
  255 
  256 #ifdef SMP
  257 /*
  258  * Switches the cpu tied to a specific callout.
  259  * The function expects a locked incoming callout cpu and returns with
  260  * locked outcoming callout cpu.
  261  */
  262 static struct callout_cpu *
  263 callout_cpu_switch(struct callout *c, struct callout_cpu *cc, int new_cpu)
  264 {
  265         struct callout_cpu *new_cc;
  266 
  267         MPASS(c != NULL && cc != NULL);
  268         CC_LOCK_ASSERT(cc);
  269 
  270         /*
  271          * Avoid interrupts and preemption firing after the callout cpu
  272          * is blocked in order to avoid deadlocks as the new thread
  273          * may be willing to acquire the callout cpu lock.
  274          */
  275         c->c_cpu = CPUBLOCK;
  276         spinlock_enter();
  277         CC_UNLOCK(cc);
  278         new_cc = CC_CPU(new_cpu);
  279         CC_LOCK(new_cc);
  280         spinlock_exit();
  281         c->c_cpu = new_cpu;
  282         return (new_cc);
  283 }
  284 #endif
  285 
  286 /*
  287  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  288  *                                 space.
  289  *
  290  *      This code is called just once, after the space reserved for the
  291  *      callout wheel has been finalized.
  292  */
  293 void
  294 kern_timeout_callwheel_init(void)
  295 {
  296         callout_cpu_init(CC_CPU(timeout_cpu));
  297 }
  298 
  299 /*
  300  * Start standard softclock thread.
  301  */
  302 void    *softclock_ih;
  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, &softclock_ih))
  315                 panic("died while creating standard software ithreads");
  316         cc->cc_cookie = softclock_ih;
  317 #ifdef SMP
  318         CPU_FOREACH(cpu) {
  319                 if (cpu == timeout_cpu)
  320                         continue;
  321                 cc = CC_CPU(cpu);
  322                 if (swi_add(NULL, "clock", softclock, cc, SWI_CLOCK,
  323                     INTR_MPSAFE, &cc->cc_cookie))
  324                         panic("died while creating standard software ithreads");
  325                 cc->cc_callout = NULL;  /* Only cpu0 handles timeout(). */
  326                 cc->cc_callwheel = malloc(
  327                     sizeof(struct callout_tailq) * callwheelsize, M_CALLOUT,
  328                     M_WAITOK);
  329                 callout_cpu_init(cc);
  330         }
  331 #endif
  332 }
  333 
  334 SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);
  335 
  336 void
  337 callout_tick(void)
  338 {
  339         struct callout_cpu *cc;
  340         int need_softclock;
  341         int bucket;
  342 
  343         /*
  344          * Process callouts at a very low cpu priority, so we don't keep the
  345          * relatively high clock interrupt priority any longer than necessary.
  346          */
  347         need_softclock = 0;
  348         cc = CC_SELF();
  349         mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
  350         cc->cc_ticks++;
  351         for (; (cc->cc_softticks - cc->cc_ticks) <= 0; cc->cc_softticks++) {
  352                 bucket = cc->cc_softticks & callwheelmask;
  353                 if (!TAILQ_EMPTY(&cc->cc_callwheel[bucket])) {
  354                         need_softclock = 1;
  355                         break;
  356                 }
  357         }
  358         mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
  359         /*
  360          * swi_sched acquires the thread lock, so we don't want to call it
  361          * with cc_lock held; incorrect locking order.
  362          */
  363         if (need_softclock)
  364                 swi_sched(cc->cc_cookie, 0);
  365 }
  366 
  367 static struct callout_cpu *
  368 callout_lock(struct callout *c)
  369 {
  370         struct callout_cpu *cc;
  371         int cpu;
  372 
  373         for (;;) {
  374                 cpu = c->c_cpu;
  375 #ifdef SMP
  376                 if (cpu == CPUBLOCK) {
  377                         while (c->c_cpu == CPUBLOCK)
  378                                 cpu_spinwait();
  379                         continue;
  380                 }
  381 #endif
  382                 cc = CC_CPU(cpu);
  383                 CC_LOCK(cc);
  384                 if (cpu == c->c_cpu)
  385                         break;
  386                 CC_UNLOCK(cc);
  387         }
  388         return (cc);
  389 }
  390 
  391 static void
  392 callout_cc_add(struct callout *c, struct callout_cpu *cc, int to_ticks,
  393     void (*func)(void *), void *arg, int cpu)
  394 {
  395 
  396         CC_LOCK_ASSERT(cc);
  397 
  398         if (to_ticks <= 0)
  399                 to_ticks = 1;
  400         c->c_arg = arg;
  401         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  402         c->c_func = func;
  403         c->c_time = cc->cc_ticks + to_ticks;
  404         TAILQ_INSERT_TAIL(&cc->cc_callwheel[c->c_time & callwheelmask],
  405             c, c_links.tqe);
  406 }
  407 
  408 static void
  409 callout_cc_del(struct callout *c, struct callout_cpu *cc)
  410 {
  411 
  412         if (cc->cc_next == c)
  413                 cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  414         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  415                 c->c_func = NULL;
  416                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  417         }
  418 }
  419 
  420 static struct callout *
  421 softclock_call_cc(struct callout *c, struct callout_cpu *cc, int *mpcalls,
  422     int *lockcalls, int *gcalls)
  423 {
  424         void (*c_func)(void *);
  425         void *c_arg;
  426         struct lock_class *class;
  427         struct lock_object *c_lock;
  428         int c_flags, sharedlock;
  429 #ifdef SMP
  430         struct callout_cpu *new_cc;
  431         void (*new_func)(void *);
  432         void *new_arg;
  433         int new_cpu, new_ticks;
  434 #endif
  435 #ifdef DIAGNOSTIC
  436         struct bintime bt1, bt2;
  437         struct timespec ts2;
  438         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  439         static timeout_t *lastfunc;
  440 #endif
  441 
  442         cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  443         class = (c->c_lock != NULL) ? LOCK_CLASS(c->c_lock) : NULL;
  444         sharedlock = (c->c_flags & CALLOUT_SHAREDLOCK) ? 0 : 1;
  445         c_lock = c->c_lock;
  446         c_func = c->c_func;
  447         c_arg = c->c_arg;
  448         c_flags = c->c_flags;
  449         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  450                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  451         else
  452                 c->c_flags &= ~CALLOUT_PENDING;
  453         cc->cc_curr = c;
  454         cc->cc_cancel = 0;
  455         CC_UNLOCK(cc);
  456         if (c_lock != NULL) {
  457                 class->lc_lock(c_lock, sharedlock);
  458                 /*
  459                  * The callout may have been cancelled
  460                  * while we switched locks.
  461                  */
  462                 if (cc->cc_cancel) {
  463                         class->lc_unlock(c_lock);
  464                         goto skip;
  465                 }
  466                 /* The callout cannot be stopped now. */
  467                 cc->cc_cancel = 1;
  468 
  469                 if (c_lock == &Giant.lock_object) {
  470                         (*gcalls)++;
  471                         CTR3(KTR_CALLOUT, "callout %p func %p arg %p",
  472                             c, c_func, c_arg);
  473                 } else {
  474                         (*lockcalls)++;
  475                         CTR3(KTR_CALLOUT, "callout lock %p func %p arg %p",
  476                             c, c_func, c_arg);
  477                 }
  478         } else {
  479                 (*mpcalls)++;
  480                 CTR3(KTR_CALLOUT, "callout mpsafe %p func %p arg %p",
  481                     c, c_func, c_arg);
  482         }
  483 #ifdef DIAGNOSTIC
  484         binuptime(&bt1);
  485 #endif
  486         THREAD_NO_SLEEPING();
  487         SDT_PROBE(callout_execute, kernel, , callout_start, c, 0, 0, 0, 0);
  488         c_func(c_arg);
  489         SDT_PROBE(callout_execute, kernel, , callout_end, c, 0, 0, 0, 0);
  490         THREAD_SLEEPING_OK();
  491 #ifdef DIAGNOSTIC
  492         binuptime(&bt2);
  493         bintime_sub(&bt2, &bt1);
  494         if (bt2.frac > maxdt) {
  495                 if (lastfunc != c_func || bt2.frac > maxdt * 2) {
  496                         bintime2timespec(&bt2, &ts2);
  497                         printf(
  498                 "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  499                             c_func, c_arg, (intmax_t)ts2.tv_sec, ts2.tv_nsec);
  500                 }
  501                 maxdt = bt2.frac;
  502                 lastfunc = c_func;
  503         }
  504 #endif
  505         CTR1(KTR_CALLOUT, "callout %p finished", c);
  506         if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
  507                 class->lc_unlock(c_lock);
  508 skip:
  509         CC_LOCK(cc);
  510         /*
  511          * If the current callout is locally allocated (from
  512          * timeout(9)) then put it on the freelist.
  513          *
  514          * Note: we need to check the cached copy of c_flags because
  515          * if it was not local, then it's not safe to deref the
  516          * callout pointer.
  517          */
  518         if (c_flags & CALLOUT_LOCAL_ALLOC) {
  519                 KASSERT(c->c_flags == CALLOUT_LOCAL_ALLOC,
  520                     ("corrupted callout"));
  521                 c->c_func = NULL;
  522                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  523         }
  524         cc->cc_curr = NULL;
  525         if (cc->cc_waiting) {
  526                 /*
  527                  * There is someone waiting for the
  528                  * callout to complete.
  529                  * If the callout was scheduled for
  530                  * migration just cancel it.
  531                  */
  532                 if (cc_cme_migrating(cc))
  533                         cc_cme_cleanup(cc);
  534                 cc->cc_waiting = 0;
  535                 CC_UNLOCK(cc);
  536                 wakeup(&cc->cc_waiting);
  537                 CC_LOCK(cc);
  538         } else if (cc_cme_migrating(cc)) {
  539 #ifdef SMP
  540                 /*
  541                  * If the callout was scheduled for
  542                  * migration just perform it now.
  543                  */
  544                 new_cpu = cc->cc_migration_cpu;
  545                 new_ticks = cc->cc_migration_ticks;
  546                 new_func = cc->cc_migration_func;
  547                 new_arg = cc->cc_migration_arg;
  548                 cc_cme_cleanup(cc);
  549 
  550                 /*
  551                  * Handle deferred callout stops
  552                  */
  553                 if ((c->c_flags & CALLOUT_DFRMIGRATION) == 0) {
  554                         CTR3(KTR_CALLOUT,
  555                              "deferred cancelled %p func %p arg %p",
  556                              c, new_func, new_arg);
  557                         callout_cc_del(c, cc);
  558                         goto nextc;
  559                 }
  560 
  561                 c->c_flags &= ~CALLOUT_DFRMIGRATION;
  562 
  563                 /*
  564                  * It should be assert here that the
  565                  * callout is not destroyed but that
  566                  * is not easy.
  567                  */
  568                 new_cc = callout_cpu_switch(c, cc, new_cpu);
  569                 callout_cc_add(c, new_cc, new_ticks, new_func, new_arg,
  570                     new_cpu);
  571                 CC_UNLOCK(new_cc);
  572                 CC_LOCK(cc);
  573 #else
  574                 panic("migration should not happen");
  575 #endif
  576         }
  577 #ifdef SMP
  578 nextc:
  579 #endif
  580         return (cc->cc_next);
  581 }
  582 
  583 /*
  584  * The callout mechanism is based on the work of Adam M. Costello and 
  585  * George Varghese, published in a technical report entitled "Redesigning
  586  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  587  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  588  * used in this implementation was published by G. Varghese and T. Lauck in
  589  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  590  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  591  * the 11th ACM Annual Symposium on Operating Systems Principles,
  592  * Austin, Texas Nov 1987.
  593  */
  594 
  595 /*
  596  * Software (low priority) clock interrupt.
  597  * Run periodic events from timeout queue.
  598  */
  599 void
  600 softclock(void *arg)
  601 {
  602         struct callout_cpu *cc;
  603         struct callout *c;
  604         struct callout_tailq *bucket;
  605         int curticks;
  606         int steps;      /* #steps since we last allowed interrupts */
  607         int depth;
  608         int mpcalls;
  609         int lockcalls;
  610         int gcalls;
  611 
  612 #ifndef MAX_SOFTCLOCK_STEPS
  613 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  614 #endif /* MAX_SOFTCLOCK_STEPS */
  615 
  616         mpcalls = 0;
  617         lockcalls = 0;
  618         gcalls = 0;
  619         depth = 0;
  620         steps = 0;
  621         cc = (struct callout_cpu *)arg;
  622         CC_LOCK(cc);
  623         while (cc->cc_softticks - 1 != cc->cc_ticks) {
  624                 /*
  625                  * cc_softticks may be modified by hard clock, so cache
  626                  * it while we work on a given bucket.
  627                  */
  628                 curticks = cc->cc_softticks;
  629                 cc->cc_softticks++;
  630                 bucket = &cc->cc_callwheel[curticks & callwheelmask];
  631                 c = TAILQ_FIRST(bucket);
  632                 while (c != NULL) {
  633                         depth++;
  634                         if (c->c_time != curticks) {
  635                                 c = TAILQ_NEXT(c, c_links.tqe);
  636                                 ++steps;
  637                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  638                                         cc->cc_next = c;
  639                                         /* Give interrupts a chance. */
  640                                         CC_UNLOCK(cc);
  641                                         ;       /* nothing */
  642                                         CC_LOCK(cc);
  643                                         c = cc->cc_next;
  644                                         steps = 0;
  645                                 }
  646                         } else {
  647                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  648                                 c = softclock_call_cc(c, cc, &mpcalls,
  649                                     &lockcalls, &gcalls);
  650                                 steps = 0;
  651                         }
  652                 }
  653         }
  654         avg_depth += (depth * 1000 - avg_depth) >> 8;
  655         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  656         avg_lockcalls += (lockcalls * 1000 - avg_lockcalls) >> 8;
  657         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  658         cc->cc_next = NULL;
  659         CC_UNLOCK(cc);
  660 }
  661 
  662 /*
  663  * timeout --
  664  *      Execute a function after a specified length of time.
  665  *
  666  * untimeout --
  667  *      Cancel previous timeout function call.
  668  *
  669  * callout_handle_init --
  670  *      Initialize a handle so that using it with untimeout is benign.
  671  *
  672  *      See AT&T BCI Driver Reference Manual for specification.  This
  673  *      implementation differs from that one in that although an 
  674  *      identification value is returned from timeout, the original
  675  *      arguments to timeout as well as the identifier are used to
  676  *      identify entries for untimeout.
  677  */
  678 struct callout_handle
  679 timeout(ftn, arg, to_ticks)
  680         timeout_t *ftn;
  681         void *arg;
  682         int to_ticks;
  683 {
  684         struct callout_cpu *cc;
  685         struct callout *new;
  686         struct callout_handle handle;
  687 
  688         cc = CC_CPU(timeout_cpu);
  689         CC_LOCK(cc);
  690         /* Fill in the next free callout structure. */
  691         new = SLIST_FIRST(&cc->cc_callfree);
  692         if (new == NULL)
  693                 /* XXX Attempt to malloc first */
  694                 panic("timeout table full");
  695         SLIST_REMOVE_HEAD(&cc->cc_callfree, c_links.sle);
  696         callout_reset(new, to_ticks, ftn, arg);
  697         handle.callout = new;
  698         CC_UNLOCK(cc);
  699 
  700         return (handle);
  701 }
  702 
  703 void
  704 untimeout(ftn, arg, handle)
  705         timeout_t *ftn;
  706         void *arg;
  707         struct callout_handle handle;
  708 {
  709         struct callout_cpu *cc;
  710 
  711         /*
  712          * Check for a handle that was initialized
  713          * by callout_handle_init, but never used
  714          * for a real timeout.
  715          */
  716         if (handle.callout == NULL)
  717                 return;
  718 
  719         cc = callout_lock(handle.callout);
  720         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  721                 callout_stop(handle.callout);
  722         CC_UNLOCK(cc);
  723 }
  724 
  725 void
  726 callout_handle_init(struct callout_handle *handle)
  727 {
  728         handle->callout = NULL;
  729 }
  730 
  731 /*
  732  * New interface; clients allocate their own callout structures.
  733  *
  734  * callout_reset() - establish or change a timeout
  735  * callout_stop() - disestablish a timeout
  736  * callout_init() - initialize a callout structure so that it can
  737  *      safely be passed to callout_reset() and callout_stop()
  738  *
  739  * <sys/callout.h> defines three convenience macros:
  740  *
  741  * callout_active() - returns truth if callout has not been stopped,
  742  *      drained, or deactivated since the last time the callout was
  743  *      reset.
  744  * callout_pending() - returns truth if callout is still waiting for timeout
  745  * callout_deactivate() - marks the callout as having been serviced
  746  */
  747 int
  748 callout_reset_on(struct callout *c, int to_ticks, void (*ftn)(void *),
  749     void *arg, int cpu)
  750 {
  751         struct callout_cpu *cc;
  752         int cancelled = 0;
  753 
  754         /*
  755          * Don't allow migration of pre-allocated callouts lest they
  756          * become unbalanced.
  757          */
  758         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  759                 cpu = c->c_cpu;
  760         cc = callout_lock(c);
  761         if (cc->cc_curr == c) {
  762                 /*
  763                  * We're being asked to reschedule a callout which is
  764                  * currently in progress.  If there is a lock then we
  765                  * can cancel the callout if it has not really started.
  766                  */
  767                 if (c->c_lock != NULL && !cc->cc_cancel)
  768                         cancelled = cc->cc_cancel = 1;
  769                 if (cc->cc_waiting) {
  770                         /*
  771                          * Someone has called callout_drain to kill this
  772                          * callout.  Don't reschedule.
  773                          */
  774                         CTR4(KTR_CALLOUT, "%s %p func %p arg %p",
  775                             cancelled ? "cancelled" : "failed to cancel",
  776                             c, c->c_func, c->c_arg);
  777                         CC_UNLOCK(cc);
  778                         return (cancelled);
  779                 }
  780         }
  781         if (c->c_flags & CALLOUT_PENDING) {
  782                 if (cc->cc_next == c) {
  783                         cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  784                 }
  785                 TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], c,
  786                     c_links.tqe);
  787 
  788                 cancelled = 1;
  789                 c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  790         }
  791 
  792 #ifdef SMP
  793         /*
  794          * If the callout must migrate try to perform it immediately.
  795          * If the callout is currently running, just defer the migration
  796          * to a more appropriate moment.
  797          */
  798         if (c->c_cpu != cpu) {
  799                 if (cc->cc_curr == c) {
  800                         cc->cc_migration_cpu = cpu;
  801                         cc->cc_migration_ticks = to_ticks;
  802                         cc->cc_migration_func = ftn;
  803                         cc->cc_migration_arg = arg;
  804                         c->c_flags |= CALLOUT_DFRMIGRATION;
  805                         CTR5(KTR_CALLOUT,
  806                     "migration of %p func %p arg %p in %d to %u deferred",
  807                             c, c->c_func, c->c_arg, to_ticks, cpu);
  808                         CC_UNLOCK(cc);
  809                         return (cancelled);
  810                 }
  811                 cc = callout_cpu_switch(c, cc, cpu);
  812         }
  813 #endif
  814 
  815         callout_cc_add(c, cc, to_ticks, ftn, arg, cpu);
  816         CTR5(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d",
  817             cancelled ? "re" : "", c, c->c_func, c->c_arg, to_ticks);
  818         CC_UNLOCK(cc);
  819 
  820         return (cancelled);
  821 }
  822 
  823 /*
  824  * Common idioms that can be optimized in the future.
  825  */
  826 int
  827 callout_schedule_on(struct callout *c, int to_ticks, int cpu)
  828 {
  829         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, cpu);
  830 }
  831 
  832 int
  833 callout_schedule(struct callout *c, int to_ticks)
  834 {
  835         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, c->c_cpu);
  836 }
  837 
  838 int
  839 _callout_stop_safe(c, safe)
  840         struct  callout *c;
  841         int     safe;
  842 {
  843         struct callout_cpu *cc, *old_cc;
  844         struct lock_class *class;
  845         int use_lock, sq_locked;
  846 
  847         /*
  848          * Some old subsystems don't hold Giant while running a callout_stop(),
  849          * so just discard this check for the moment.
  850          */
  851         if (!safe && c->c_lock != NULL) {
  852                 if (c->c_lock == &Giant.lock_object)
  853                         use_lock = mtx_owned(&Giant);
  854                 else {
  855                         use_lock = 1;
  856                         class = LOCK_CLASS(c->c_lock);
  857                         class->lc_assert(c->c_lock, LA_XLOCKED);
  858                 }
  859         } else
  860                 use_lock = 0;
  861 
  862         sq_locked = 0;
  863         old_cc = NULL;
  864 again:
  865         cc = callout_lock(c);
  866 
  867         /*
  868          * If the callout was migrating while the callout cpu lock was
  869          * dropped,  just drop the sleepqueue lock and check the states
  870          * again.
  871          */
  872         if (sq_locked != 0 && cc != old_cc) {
  873 #ifdef SMP
  874                 CC_UNLOCK(cc);
  875                 sleepq_release(&old_cc->cc_waiting);
  876                 sq_locked = 0;
  877                 old_cc = NULL;
  878                 goto again;
  879 #else
  880                 panic("migration should not happen");
  881 #endif
  882         }
  883 
  884         /*
  885          * If the callout isn't pending, it's not on the queue, so
  886          * don't attempt to remove it from the queue.  We can try to
  887          * stop it by other means however.
  888          */
  889         if (!(c->c_flags & CALLOUT_PENDING)) {
  890                 c->c_flags &= ~CALLOUT_ACTIVE;
  891 
  892                 /*
  893                  * If it wasn't on the queue and it isn't the current
  894                  * callout, then we can't stop it, so just bail.
  895                  */
  896                 if (cc->cc_curr != c) {
  897                         CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  898                             c, c->c_func, c->c_arg);
  899                         CC_UNLOCK(cc);
  900                         if (sq_locked)
  901                                 sleepq_release(&cc->cc_waiting);
  902                         return (0);
  903                 }
  904 
  905                 if (safe) {
  906                         /*
  907                          * The current callout is running (or just
  908                          * about to run) and blocking is allowed, so
  909                          * just wait for the current invocation to
  910                          * finish.
  911                          */
  912                         while (cc->cc_curr == c) {
  913 
  914                                 /*
  915                                  * Use direct calls to sleepqueue interface
  916                                  * instead of cv/msleep in order to avoid
  917                                  * a LOR between cc_lock and sleepqueue
  918                                  * chain spinlocks.  This piece of code
  919                                  * emulates a msleep_spin() call actually.
  920                                  *
  921                                  * If we already have the sleepqueue chain
  922                                  * locked, then we can safely block.  If we
  923                                  * don't already have it locked, however,
  924                                  * we have to drop the cc_lock to lock
  925                                  * it.  This opens several races, so we
  926                                  * restart at the beginning once we have
  927                                  * both locks.  If nothing has changed, then
  928                                  * we will end up back here with sq_locked
  929                                  * set.
  930                                  */
  931                                 if (!sq_locked) {
  932                                         CC_UNLOCK(cc);
  933                                         sleepq_lock(&cc->cc_waiting);
  934                                         sq_locked = 1;
  935                                         old_cc = cc;
  936                                         goto again;
  937                                 }
  938 
  939                                 /*
  940                                  * Migration could be cancelled here, but
  941                                  * as long as it is still not sure when it
  942                                  * will be packed up, just let softclock()
  943                                  * take care of it.
  944                                  */
  945                                 cc->cc_waiting = 1;
  946                                 DROP_GIANT();
  947                                 CC_UNLOCK(cc);
  948                                 sleepq_add(&cc->cc_waiting,
  949                                     &cc->cc_lock.lock_object, "codrain",
  950                                     SLEEPQ_SLEEP, 0);
  951                                 sleepq_wait(&cc->cc_waiting, 0);
  952                                 sq_locked = 0;
  953                                 old_cc = NULL;
  954 
  955                                 /* Reacquire locks previously released. */
  956                                 PICKUP_GIANT();
  957                                 CC_LOCK(cc);
  958                         }
  959                 } else if (use_lock && !cc->cc_cancel) {
  960                         /*
  961                          * The current callout is waiting for its
  962                          * lock which we hold.  Cancel the callout
  963                          * and return.  After our caller drops the
  964                          * lock, the callout will be skipped in
  965                          * softclock().
  966                          */
  967                         cc->cc_cancel = 1;
  968                         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
  969                             c, c->c_func, c->c_arg);
  970                         KASSERT(!cc_cme_migrating(cc),
  971                             ("callout wrongly scheduled for migration"));
  972                         CC_UNLOCK(cc);
  973                         KASSERT(!sq_locked, ("sleepqueue chain locked"));
  974                         return (1);
  975                 } else if ((c->c_flags & CALLOUT_DFRMIGRATION) != 0) {
  976                         c->c_flags &= ~CALLOUT_DFRMIGRATION;
  977                         CTR3(KTR_CALLOUT, "postponing stop %p func %p arg %p",
  978                             c, c->c_func, c->c_arg);
  979                         CC_UNLOCK(cc);
  980                         return (1);
  981                 }
  982                 CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  983                     c, c->c_func, c->c_arg);
  984                 CC_UNLOCK(cc);
  985                 KASSERT(!sq_locked, ("sleepqueue chain still locked"));
  986                 return (0);
  987         }
  988         if (sq_locked)
  989                 sleepq_release(&cc->cc_waiting);
  990 
  991         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  992 
  993         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
  994             c, c->c_func, c->c_arg);
  995         TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], c,
  996             c_links.tqe);
  997         callout_cc_del(c, cc);
  998 
  999         CC_UNLOCK(cc);
 1000         return (1);
 1001 }
 1002 
 1003 void
 1004 callout_init(c, mpsafe)
 1005         struct  callout *c;
 1006         int mpsafe;
 1007 {
 1008         bzero(c, sizeof *c);
 1009         if (mpsafe) {
 1010                 c->c_lock = NULL;
 1011                 c->c_flags = CALLOUT_RETURNUNLOCKED;
 1012         } else {
 1013                 c->c_lock = &Giant.lock_object;
 1014                 c->c_flags = 0;
 1015         }
 1016         c->c_cpu = timeout_cpu;
 1017 }
 1018 
 1019 void
 1020 _callout_init_lock(c, lock, flags)
 1021         struct  callout *c;
 1022         struct  lock_object *lock;
 1023         int flags;
 1024 {
 1025         bzero(c, sizeof *c);
 1026         c->c_lock = lock;
 1027         KASSERT((flags & ~(CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK)) == 0,
 1028             ("callout_init_lock: bad flags %d", flags));
 1029         KASSERT(lock != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
 1030             ("callout_init_lock: CALLOUT_RETURNUNLOCKED with no lock"));
 1031         KASSERT(lock == NULL || !(LOCK_CLASS(lock)->lc_flags &
 1032             (LC_SPINLOCK | LC_SLEEPABLE)), ("%s: invalid lock class",
 1033             __func__));
 1034         c->c_flags = flags & (CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK);
 1035         c->c_cpu = timeout_cpu;
 1036 }
 1037 
 1038 #ifdef APM_FIXUP_CALLTODO
 1039 /* 
 1040  * Adjust the kernel calltodo timeout list.  This routine is used after 
 1041  * an APM resume to recalculate the calltodo timer list values with the 
 1042  * number of hz's we have been sleeping.  The next hardclock() will detect 
 1043  * that there are fired timers and run softclock() to execute them.
 1044  *
 1045  * Please note, I have not done an exhaustive analysis of what code this
 1046  * might break.  I am motivated to have my select()'s and alarm()'s that
 1047  * have expired during suspend firing upon resume so that the applications
 1048  * which set the timer can do the maintanence the timer was for as close
 1049  * as possible to the originally intended time.  Testing this code for a 
 1050  * week showed that resuming from a suspend resulted in 22 to 25 timers 
 1051  * firing, which seemed independant on whether the suspend was 2 hours or
 1052  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
 1053  */
 1054 void
 1055 adjust_timeout_calltodo(time_change)
 1056     struct timeval *time_change;
 1057 {
 1058         register struct callout *p;
 1059         unsigned long delta_ticks;
 1060 
 1061         /* 
 1062          * How many ticks were we asleep?
 1063          * (stolen from tvtohz()).
 1064          */
 1065 
 1066         /* Don't do anything */
 1067         if (time_change->tv_sec < 0)
 1068                 return;
 1069         else if (time_change->tv_sec <= LONG_MAX / 1000000)
 1070                 delta_ticks = (time_change->tv_sec * 1000000 +
 1071                                time_change->tv_usec + (tick - 1)) / tick + 1;
 1072         else if (time_change->tv_sec <= LONG_MAX / hz)
 1073                 delta_ticks = time_change->tv_sec * hz +
 1074                               (time_change->tv_usec + (tick - 1)) / tick + 1;
 1075         else
 1076                 delta_ticks = LONG_MAX;
 1077 
 1078         if (delta_ticks > INT_MAX)
 1079                 delta_ticks = INT_MAX;
 1080 
 1081         /* 
 1082          * Now rip through the timer calltodo list looking for timers
 1083          * to expire.
 1084          */
 1085 
 1086         /* don't collide with softclock() */
 1087         CC_LOCK(cc);
 1088         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
 1089                 p->c_time -= delta_ticks;
 1090 
 1091                 /* Break if the timer had more time on it than delta_ticks */
 1092                 if (p->c_time > 0)
 1093                         break;
 1094 
 1095                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
 1096                 delta_ticks = -p->c_time;
 1097         }
 1098         CC_UNLOCK(cc);
 1099 
 1100         return;
 1101 }
 1102 #endif /* APM_FIXUP_CALLTODO */

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