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: head/sys/kern/kern_timeout.c 268026 2014-06-30 04:25:51Z adrian $");
   39 
   40 #include "opt_callout_profiling.h"
   41 #if defined(__arm__)
   42 #include "opt_timer.h"
   43 #endif
   44 #include "opt_rss.h"
   45 
   46 #include <sys/param.h>
   47 #include <sys/systm.h>
   48 #include <sys/bus.h>
   49 #include <sys/callout.h>
   50 #include <sys/file.h>
   51 #include <sys/interrupt.h>
   52 #include <sys/kernel.h>
   53 #include <sys/ktr.h>
   54 #include <sys/lock.h>
   55 #include <sys/malloc.h>
   56 #include <sys/mutex.h>
   57 #include <sys/proc.h>
   58 #include <sys/sdt.h>
   59 #include <sys/sleepqueue.h>
   60 #include <sys/sysctl.h>
   61 #include <sys/smp.h>
   62 
   63 #ifdef SMP
   64 #include <machine/cpu.h>
   65 #endif
   66 
   67 #ifndef NO_EVENTTIMERS
   68 DPCPU_DECLARE(sbintime_t, hardclocktime);
   69 #endif
   70 
   71 SDT_PROVIDER_DEFINE(callout_execute);
   72 SDT_PROBE_DEFINE1(callout_execute, kernel, , callout__start,
   73     "struct callout *");
   74 SDT_PROBE_DEFINE1(callout_execute, kernel, , callout__end,
   75     "struct callout *");
   76 
   77 #ifdef CALLOUT_PROFILING
   78 static int avg_depth;
   79 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
   80     "Average number of items examined per softclock call. Units = 1/1000");
   81 static int avg_gcalls;
   82 SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
   83     "Average number of Giant callouts made per softclock call. Units = 1/1000");
   84 static int avg_lockcalls;
   85 SYSCTL_INT(_debug, OID_AUTO, to_avg_lockcalls, CTLFLAG_RD, &avg_lockcalls, 0,
   86     "Average number of lock callouts made per softclock call. Units = 1/1000");
   87 static int avg_mpcalls;
   88 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
   89     "Average number of MP callouts made per softclock call. Units = 1/1000");
   90 static int avg_depth_dir;
   91 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth_dir, CTLFLAG_RD, &avg_depth_dir, 0,
   92     "Average number of direct callouts examined per callout_process call. "
   93     "Units = 1/1000");
   94 static int avg_lockcalls_dir;
   95 SYSCTL_INT(_debug, OID_AUTO, to_avg_lockcalls_dir, CTLFLAG_RD,
   96     &avg_lockcalls_dir, 0, "Average number of lock direct callouts made per "
   97     "callout_process call. Units = 1/1000");
   98 static int avg_mpcalls_dir;
   99 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls_dir, CTLFLAG_RD, &avg_mpcalls_dir,
  100     0, "Average number of MP direct callouts made per callout_process call. "
  101     "Units = 1/1000");
  102 #endif
  103 
  104 static int ncallout;
  105 SYSCTL_INT(_kern, OID_AUTO, ncallout, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, &ncallout, 0,
  106     "Number of entries in callwheel and size of timeout() preallocation");
  107 
  108 #ifdef  RSS
  109 static int pin_default_swi = 1;
  110 static int pin_pcpu_swi = 1;
  111 #else
  112 static int pin_default_swi = 0;
  113 static int pin_pcpu_swi = 0;
  114 #endif
  115 
  116 SYSCTL_INT(_kern, OID_AUTO, pin_default_swi, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, &pin_default_swi,
  117     0, "Pin the default (non-per-cpu) swi (shared with PCPU 0 swi)");
  118 SYSCTL_INT(_kern, OID_AUTO, pin_pcpu_swi, CTLFLAG_RDTUN | CTLFLAG_NOFETCH, &pin_pcpu_swi,
  119     0, "Pin the per-CPU swis (except PCPU 0, which is also default");
  120 
  121 /*
  122  * TODO:
  123  *      allocate more timeout table slots when table overflows.
  124  */
  125 u_int callwheelsize, callwheelmask;
  126 
  127 /*
  128  * The callout cpu exec entities represent informations necessary for
  129  * describing the state of callouts currently running on the CPU and the ones
  130  * necessary for migrating callouts to the new callout cpu. In particular,
  131  * the first entry of the array cc_exec_entity holds informations for callout
  132  * running in SWI thread context, while the second one holds informations
  133  * for callout running directly from hardware interrupt context.
  134  * The cached informations are very important for deferring migration when
  135  * the migrating callout is already running.
  136  */
  137 struct cc_exec {
  138         struct callout          *cc_next;
  139         struct callout          *cc_curr;
  140 #ifdef SMP
  141         void                    (*ce_migration_func)(void *);
  142         void                    *ce_migration_arg;
  143         int                     ce_migration_cpu;
  144         sbintime_t              ce_migration_time;
  145         sbintime_t              ce_migration_prec;
  146 #endif
  147         bool                    cc_cancel;
  148         bool                    cc_waiting;
  149 };
  150 
  151 /*
  152  * There is one struct callout_cpu per cpu, holding all relevant
  153  * state for the callout processing thread on the individual CPU.
  154  */
  155 struct callout_cpu {
  156         struct mtx_padalign     cc_lock;
  157         struct cc_exec          cc_exec_entity[2];
  158         struct callout          *cc_callout;
  159         struct callout_list     *cc_callwheel;
  160         struct callout_tailq    cc_expireq;
  161         struct callout_slist    cc_callfree;
  162         sbintime_t              cc_firstevent;
  163         sbintime_t              cc_lastscan;
  164         void                    *cc_cookie;
  165         u_int                   cc_bucket;
  166 };
  167 
  168 #define cc_exec_curr            cc_exec_entity[0].cc_curr
  169 #define cc_exec_next            cc_exec_entity[0].cc_next
  170 #define cc_exec_cancel          cc_exec_entity[0].cc_cancel
  171 #define cc_exec_waiting         cc_exec_entity[0].cc_waiting
  172 #define cc_exec_curr_dir        cc_exec_entity[1].cc_curr
  173 #define cc_exec_next_dir        cc_exec_entity[1].cc_next
  174 #define cc_exec_cancel_dir      cc_exec_entity[1].cc_cancel
  175 #define cc_exec_waiting_dir     cc_exec_entity[1].cc_waiting
  176 
  177 #ifdef SMP
  178 #define cc_migration_func       cc_exec_entity[0].ce_migration_func
  179 #define cc_migration_arg        cc_exec_entity[0].ce_migration_arg
  180 #define cc_migration_cpu        cc_exec_entity[0].ce_migration_cpu
  181 #define cc_migration_time       cc_exec_entity[0].ce_migration_time
  182 #define cc_migration_prec       cc_exec_entity[0].ce_migration_prec
  183 #define cc_migration_func_dir   cc_exec_entity[1].ce_migration_func
  184 #define cc_migration_arg_dir    cc_exec_entity[1].ce_migration_arg
  185 #define cc_migration_cpu_dir    cc_exec_entity[1].ce_migration_cpu
  186 #define cc_migration_time_dir   cc_exec_entity[1].ce_migration_time
  187 #define cc_migration_prec_dir   cc_exec_entity[1].ce_migration_prec
  188 
  189 struct callout_cpu cc_cpu[MAXCPU];
  190 #define CPUBLOCK        MAXCPU
  191 #define CC_CPU(cpu)     (&cc_cpu[(cpu)])
  192 #define CC_SELF()       CC_CPU(PCPU_GET(cpuid))
  193 #else
  194 struct callout_cpu cc_cpu;
  195 #define CC_CPU(cpu)     &cc_cpu
  196 #define CC_SELF()       &cc_cpu
  197 #endif
  198 #define CC_LOCK(cc)     mtx_lock_spin(&(cc)->cc_lock)
  199 #define CC_UNLOCK(cc)   mtx_unlock_spin(&(cc)->cc_lock)
  200 #define CC_LOCK_ASSERT(cc)      mtx_assert(&(cc)->cc_lock, MA_OWNED)
  201 
  202 static int timeout_cpu;
  203 
  204 static void     callout_cpu_init(struct callout_cpu *cc);
  205 static void     softclock_call_cc(struct callout *c, struct callout_cpu *cc,
  206 #ifdef CALLOUT_PROFILING
  207                     int *mpcalls, int *lockcalls, int *gcalls,
  208 #endif
  209                     int direct);
  210 
  211 static MALLOC_DEFINE(M_CALLOUT, "callout", "Callout datastructures");
  212 
  213 /**
  214  * Locked by cc_lock:
  215  *   cc_curr         - If a callout is in progress, it is cc_curr.
  216  *                     If cc_curr is non-NULL, threads waiting in
  217  *                     callout_drain() will be woken up as soon as the
  218  *                     relevant callout completes.
  219  *   cc_cancel       - Changing to 1 with both callout_lock and cc_lock held
  220  *                     guarantees that the current callout will not run.
  221  *                     The softclock() function sets this to 0 before it
  222  *                     drops callout_lock to acquire c_lock, and it calls
  223  *                     the handler only if curr_cancelled is still 0 after
  224  *                     cc_lock is successfully acquired.
  225  *   cc_waiting      - If a thread is waiting in callout_drain(), then
  226  *                     callout_wait is nonzero.  Set only when
  227  *                     cc_curr is non-NULL.
  228  */
  229 
  230 /*
  231  * Resets the execution entity tied to a specific callout cpu.
  232  */
  233 static void
  234 cc_cce_cleanup(struct callout_cpu *cc, int direct)
  235 {
  236 
  237         cc->cc_exec_entity[direct].cc_curr = NULL;
  238         cc->cc_exec_entity[direct].cc_next = NULL;
  239         cc->cc_exec_entity[direct].cc_cancel = false;
  240         cc->cc_exec_entity[direct].cc_waiting = false;
  241 #ifdef SMP
  242         cc->cc_exec_entity[direct].ce_migration_cpu = CPUBLOCK;
  243         cc->cc_exec_entity[direct].ce_migration_time = 0;
  244         cc->cc_exec_entity[direct].ce_migration_prec = 0;
  245         cc->cc_exec_entity[direct].ce_migration_func = NULL;
  246         cc->cc_exec_entity[direct].ce_migration_arg = NULL;
  247 #endif
  248 }
  249 
  250 /*
  251  * Checks if migration is requested by a specific callout cpu.
  252  */
  253 static int
  254 cc_cce_migrating(struct callout_cpu *cc, int direct)
  255 {
  256 
  257 #ifdef SMP
  258         return (cc->cc_exec_entity[direct].ce_migration_cpu != CPUBLOCK);
  259 #else
  260         return (0);
  261 #endif
  262 }
  263 
  264 /*
  265  * Kernel low level callwheel initialization
  266  * called on cpu0 during kernel startup.
  267  */
  268 static void
  269 callout_callwheel_init(void *dummy)
  270 {
  271         struct callout_cpu *cc;
  272 
  273         /*
  274          * Calculate the size of the callout wheel and the preallocated
  275          * timeout() structures.
  276          * XXX: Clip callout to result of previous function of maxusers
  277          * maximum 384.  This is still huge, but acceptable.
  278          */
  279         ncallout = imin(16 + maxproc + maxfiles, 18508);
  280         TUNABLE_INT_FETCH("kern.ncallout", &ncallout);
  281 
  282         /*
  283          * Calculate callout wheel size, should be next power of two higher
  284          * than 'ncallout'.
  285          */
  286         callwheelsize = 1 << fls(ncallout);
  287         callwheelmask = callwheelsize - 1;
  288 
  289         /*
  290          * Fetch whether we're pinning the swi's or not.
  291          */
  292         TUNABLE_INT_FETCH("kern.pin_default_swi", &pin_default_swi);
  293         TUNABLE_INT_FETCH("kern.pin_pcpu_swi", &pin_pcpu_swi);
  294 
  295         /*
  296          * Only cpu0 handles timeout(9) and receives a preallocation.
  297          *
  298          * XXX: Once all timeout(9) consumers are converted this can
  299          * be removed.
  300          */
  301         timeout_cpu = PCPU_GET(cpuid);
  302         cc = CC_CPU(timeout_cpu);
  303         cc->cc_callout = malloc(ncallout * sizeof(struct callout),
  304             M_CALLOUT, M_WAITOK);
  305         callout_cpu_init(cc);
  306 }
  307 SYSINIT(callwheel_init, SI_SUB_CPU, SI_ORDER_ANY, callout_callwheel_init, NULL);
  308 
  309 /*
  310  * Initialize the per-cpu callout structures.
  311  */
  312 static void
  313 callout_cpu_init(struct callout_cpu *cc)
  314 {
  315         struct callout *c;
  316         int i;
  317 
  318         mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  319         SLIST_INIT(&cc->cc_callfree);
  320         cc->cc_callwheel = malloc(sizeof(struct callout_list) * callwheelsize,
  321             M_CALLOUT, M_WAITOK);
  322         for (i = 0; i < callwheelsize; i++)
  323                 LIST_INIT(&cc->cc_callwheel[i]);
  324         TAILQ_INIT(&cc->cc_expireq);
  325         cc->cc_firstevent = SBT_MAX;
  326         for (i = 0; i < 2; i++)
  327                 cc_cce_cleanup(cc, i);
  328         if (cc->cc_callout == NULL)     /* Only cpu0 handles timeout(9) */
  329                 return;
  330         for (i = 0; i < ncallout; i++) {
  331                 c = &cc->cc_callout[i];
  332                 callout_init(c, 0);
  333                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  334                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  335         }
  336 }
  337 
  338 #ifdef SMP
  339 /*
  340  * Switches the cpu tied to a specific callout.
  341  * The function expects a locked incoming callout cpu and returns with
  342  * locked outcoming callout cpu.
  343  */
  344 static struct callout_cpu *
  345 callout_cpu_switch(struct callout *c, struct callout_cpu *cc, int new_cpu)
  346 {
  347         struct callout_cpu *new_cc;
  348 
  349         MPASS(c != NULL && cc != NULL);
  350         CC_LOCK_ASSERT(cc);
  351 
  352         /*
  353          * Avoid interrupts and preemption firing after the callout cpu
  354          * is blocked in order to avoid deadlocks as the new thread
  355          * may be willing to acquire the callout cpu lock.
  356          */
  357         c->c_cpu = CPUBLOCK;
  358         spinlock_enter();
  359         CC_UNLOCK(cc);
  360         new_cc = CC_CPU(new_cpu);
  361         CC_LOCK(new_cc);
  362         spinlock_exit();
  363         c->c_cpu = new_cpu;
  364         return (new_cc);
  365 }
  366 #endif
  367 
  368 /*
  369  * Start standard softclock thread.
  370  */
  371 static void
  372 start_softclock(void *dummy)
  373 {
  374         struct callout_cpu *cc;
  375         char name[MAXCOMLEN];
  376 #ifdef SMP
  377         int cpu;
  378         struct intr_event *ie;
  379 #endif
  380 
  381         cc = CC_CPU(timeout_cpu);
  382         snprintf(name, sizeof(name), "clock (%d)", timeout_cpu);
  383         if (swi_add(&clk_intr_event, name, softclock, cc, SWI_CLOCK,
  384             INTR_MPSAFE, &cc->cc_cookie))
  385                 panic("died while creating standard software ithreads");
  386         if (pin_default_swi &&
  387             (intr_event_bind(clk_intr_event, timeout_cpu) != 0)) {
  388                 printf("%s: timeout clock couldn't be pinned to cpu %d\n",
  389                     __func__,
  390                     timeout_cpu);
  391         }
  392 
  393 #ifdef SMP
  394         CPU_FOREACH(cpu) {
  395                 if (cpu == timeout_cpu)
  396                         continue;
  397                 cc = CC_CPU(cpu);
  398                 cc->cc_callout = NULL;  /* Only cpu0 handles timeout(9). */
  399                 callout_cpu_init(cc);
  400                 snprintf(name, sizeof(name), "clock (%d)", cpu);
  401                 ie = NULL;
  402                 if (swi_add(&ie, name, softclock, cc, SWI_CLOCK,
  403                     INTR_MPSAFE, &cc->cc_cookie))
  404                         panic("died while creating standard software ithreads");
  405                 if (pin_pcpu_swi && (intr_event_bind(ie, cpu) != 0)) {
  406                         printf("%s: per-cpu clock couldn't be pinned to "
  407                             "cpu %d\n",
  408                             __func__,
  409                             cpu);
  410                 }
  411         }
  412 #endif
  413 }
  414 SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);
  415 
  416 #define CC_HASH_SHIFT   8
  417 
  418 static inline u_int
  419 callout_hash(sbintime_t sbt)
  420 {
  421 
  422         return (sbt >> (32 - CC_HASH_SHIFT));
  423 }
  424 
  425 static inline u_int
  426 callout_get_bucket(sbintime_t sbt)
  427 {
  428 
  429         return (callout_hash(sbt) & callwheelmask);
  430 }
  431 
  432 void
  433 callout_process(sbintime_t now)
  434 {
  435         struct callout *tmp, *tmpn;
  436         struct callout_cpu *cc;
  437         struct callout_list *sc;
  438         sbintime_t first, last, max, tmp_max;
  439         uint32_t lookahead;
  440         u_int firstb, lastb, nowb;
  441 #ifdef CALLOUT_PROFILING
  442         int depth_dir = 0, mpcalls_dir = 0, lockcalls_dir = 0;
  443 #endif
  444 
  445         cc = CC_SELF();
  446         mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
  447 
  448         /* Compute the buckets of the last scan and present times. */
  449         firstb = callout_hash(cc->cc_lastscan);
  450         cc->cc_lastscan = now;
  451         nowb = callout_hash(now);
  452 
  453         /* Compute the last bucket and minimum time of the bucket after it. */
  454         if (nowb == firstb)
  455                 lookahead = (SBT_1S / 16);
  456         else if (nowb - firstb == 1)
  457                 lookahead = (SBT_1S / 8);
  458         else
  459                 lookahead = (SBT_1S / 2);
  460         first = last = now;
  461         first += (lookahead / 2);
  462         last += lookahead;
  463         last &= (0xffffffffffffffffLLU << (32 - CC_HASH_SHIFT));
  464         lastb = callout_hash(last) - 1;
  465         max = last;
  466 
  467         /*
  468          * Check if we wrapped around the entire wheel from the last scan.
  469          * In case, we need to scan entirely the wheel for pending callouts.
  470          */
  471         if (lastb - firstb >= callwheelsize) {
  472                 lastb = firstb + callwheelsize - 1;
  473                 if (nowb - firstb >= callwheelsize)
  474                         nowb = lastb;
  475         }
  476 
  477         /* Iterate callwheel from firstb to nowb and then up to lastb. */
  478         do {
  479                 sc = &cc->cc_callwheel[firstb & callwheelmask];
  480                 tmp = LIST_FIRST(sc);
  481                 while (tmp != NULL) {
  482                         /* Run the callout if present time within allowed. */
  483                         if (tmp->c_time <= now) {
  484                                 /*
  485                                  * Consumer told us the callout may be run
  486                                  * directly from hardware interrupt context.
  487                                  */
  488                                 if (tmp->c_flags & CALLOUT_DIRECT) {
  489 #ifdef CALLOUT_PROFILING
  490                                         ++depth_dir;
  491 #endif
  492                                         cc->cc_exec_next_dir =
  493                                             LIST_NEXT(tmp, c_links.le);
  494                                         cc->cc_bucket = firstb & callwheelmask;
  495                                         LIST_REMOVE(tmp, c_links.le);
  496                                         softclock_call_cc(tmp, cc,
  497 #ifdef CALLOUT_PROFILING
  498                                             &mpcalls_dir, &lockcalls_dir, NULL,
  499 #endif
  500                                             1);
  501                                         tmp = cc->cc_exec_next_dir;
  502                                 } else {
  503                                         tmpn = LIST_NEXT(tmp, c_links.le);
  504                                         LIST_REMOVE(tmp, c_links.le);
  505                                         TAILQ_INSERT_TAIL(&cc->cc_expireq,
  506                                             tmp, c_links.tqe);
  507                                         tmp->c_flags |= CALLOUT_PROCESSED;
  508                                         tmp = tmpn;
  509                                 }
  510                                 continue;
  511                         }
  512                         /* Skip events from distant future. */
  513                         if (tmp->c_time >= max)
  514                                 goto next;
  515                         /*
  516                          * Event minimal time is bigger than present maximal
  517                          * time, so it cannot be aggregated.
  518                          */
  519                         if (tmp->c_time > last) {
  520                                 lastb = nowb;
  521                                 goto next;
  522                         }
  523                         /* Update first and last time, respecting this event. */
  524                         if (tmp->c_time < first)
  525                                 first = tmp->c_time;
  526                         tmp_max = tmp->c_time + tmp->c_precision;
  527                         if (tmp_max < last)
  528                                 last = tmp_max;
  529 next:
  530                         tmp = LIST_NEXT(tmp, c_links.le);
  531                 }
  532                 /* Proceed with the next bucket. */
  533                 firstb++;
  534                 /*
  535                  * Stop if we looked after present time and found
  536                  * some event we can't execute at now.
  537                  * Stop if we looked far enough into the future.
  538                  */
  539         } while (((int)(firstb - lastb)) <= 0);
  540         cc->cc_firstevent = last;
  541 #ifndef NO_EVENTTIMERS
  542         cpu_new_callout(curcpu, last, first);
  543 #endif
  544 #ifdef CALLOUT_PROFILING
  545         avg_depth_dir += (depth_dir * 1000 - avg_depth_dir) >> 8;
  546         avg_mpcalls_dir += (mpcalls_dir * 1000 - avg_mpcalls_dir) >> 8;
  547         avg_lockcalls_dir += (lockcalls_dir * 1000 - avg_lockcalls_dir) >> 8;
  548 #endif
  549         mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
  550         /*
  551          * swi_sched acquires the thread lock, so we don't want to call it
  552          * with cc_lock held; incorrect locking order.
  553          */
  554         if (!TAILQ_EMPTY(&cc->cc_expireq))
  555                 swi_sched(cc->cc_cookie, 0);
  556 }
  557 
  558 static struct callout_cpu *
  559 callout_lock(struct callout *c)
  560 {
  561         struct callout_cpu *cc;
  562         int cpu;
  563 
  564         for (;;) {
  565                 cpu = c->c_cpu;
  566 #ifdef SMP
  567                 if (cpu == CPUBLOCK) {
  568                         while (c->c_cpu == CPUBLOCK)
  569                                 cpu_spinwait();
  570                         continue;
  571                 }
  572 #endif
  573                 cc = CC_CPU(cpu);
  574                 CC_LOCK(cc);
  575                 if (cpu == c->c_cpu)
  576                         break;
  577                 CC_UNLOCK(cc);
  578         }
  579         return (cc);
  580 }
  581 
  582 static void
  583 callout_cc_add(struct callout *c, struct callout_cpu *cc,
  584     sbintime_t sbt, sbintime_t precision, void (*func)(void *),
  585     void *arg, int cpu, int flags)
  586 {
  587         int bucket;
  588 
  589         CC_LOCK_ASSERT(cc);
  590         if (sbt < cc->cc_lastscan)
  591                 sbt = cc->cc_lastscan;
  592         c->c_arg = arg;
  593         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  594         if (flags & C_DIRECT_EXEC)
  595                 c->c_flags |= CALLOUT_DIRECT;
  596         c->c_flags &= ~CALLOUT_PROCESSED;
  597         c->c_func = func;
  598         c->c_time = sbt;
  599         c->c_precision = precision;
  600         bucket = callout_get_bucket(c->c_time);
  601         CTR3(KTR_CALLOUT, "precision set for %p: %d.%08x",
  602             c, (int)(c->c_precision >> 32),
  603             (u_int)(c->c_precision & 0xffffffff));
  604         LIST_INSERT_HEAD(&cc->cc_callwheel[bucket], c, c_links.le);
  605         if (cc->cc_bucket == bucket)
  606                 cc->cc_exec_next_dir = c;
  607 #ifndef NO_EVENTTIMERS
  608         /*
  609          * Inform the eventtimers(4) subsystem there's a new callout
  610          * that has been inserted, but only if really required.
  611          */
  612         if (SBT_MAX - c->c_time < c->c_precision)
  613                 c->c_precision = SBT_MAX - c->c_time;
  614         sbt = c->c_time + c->c_precision;
  615         if (sbt < cc->cc_firstevent) {
  616                 cc->cc_firstevent = sbt;
  617                 cpu_new_callout(cpu, sbt, c->c_time);
  618         }
  619 #endif
  620 }
  621 
  622 static void
  623 callout_cc_del(struct callout *c, struct callout_cpu *cc)
  624 {
  625 
  626         if ((c->c_flags & CALLOUT_LOCAL_ALLOC) == 0)
  627                 return;
  628         c->c_func = NULL;
  629         SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  630 }
  631 
  632 static void
  633 softclock_call_cc(struct callout *c, struct callout_cpu *cc,
  634 #ifdef CALLOUT_PROFILING
  635     int *mpcalls, int *lockcalls, int *gcalls,
  636 #endif
  637     int direct)
  638 {
  639         struct rm_priotracker tracker;
  640         void (*c_func)(void *);
  641         void *c_arg;
  642         struct lock_class *class;
  643         struct lock_object *c_lock;
  644         uintptr_t lock_status;
  645         int c_flags;
  646 #ifdef SMP
  647         struct callout_cpu *new_cc;
  648         void (*new_func)(void *);
  649         void *new_arg;
  650         int flags, new_cpu;
  651         sbintime_t new_prec, new_time;
  652 #endif
  653 #if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING) 
  654         sbintime_t sbt1, sbt2;
  655         struct timespec ts2;
  656         static sbintime_t maxdt = 2 * SBT_1MS;  /* 2 msec */
  657         static timeout_t *lastfunc;
  658 #endif
  659 
  660         KASSERT((c->c_flags & (CALLOUT_PENDING | CALLOUT_ACTIVE)) ==
  661             (CALLOUT_PENDING | CALLOUT_ACTIVE),
  662             ("softclock_call_cc: pend|act %p %x", c, c->c_flags));
  663         class = (c->c_lock != NULL) ? LOCK_CLASS(c->c_lock) : NULL;
  664         lock_status = 0;
  665         if (c->c_flags & CALLOUT_SHAREDLOCK) {
  666                 if (class == &lock_class_rm)
  667                         lock_status = (uintptr_t)&tracker;
  668                 else
  669                         lock_status = 1;
  670         }
  671         c_lock = c->c_lock;
  672         c_func = c->c_func;
  673         c_arg = c->c_arg;
  674         c_flags = c->c_flags;
  675         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  676                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  677         else
  678                 c->c_flags &= ~CALLOUT_PENDING;
  679         cc->cc_exec_entity[direct].cc_curr = c;
  680         cc->cc_exec_entity[direct].cc_cancel = false;
  681         CC_UNLOCK(cc);
  682         if (c_lock != NULL) {
  683                 class->lc_lock(c_lock, lock_status);
  684                 /*
  685                  * The callout may have been cancelled
  686                  * while we switched locks.
  687                  */
  688                 if (cc->cc_exec_entity[direct].cc_cancel) {
  689                         class->lc_unlock(c_lock);
  690                         goto skip;
  691                 }
  692                 /* The callout cannot be stopped now. */
  693                 cc->cc_exec_entity[direct].cc_cancel = true;
  694                 if (c_lock == &Giant.lock_object) {
  695 #ifdef CALLOUT_PROFILING
  696                         (*gcalls)++;
  697 #endif
  698                         CTR3(KTR_CALLOUT, "callout giant %p func %p arg %p",
  699                             c, c_func, c_arg);
  700                 } else {
  701 #ifdef CALLOUT_PROFILING
  702                         (*lockcalls)++;
  703 #endif
  704                         CTR3(KTR_CALLOUT, "callout lock %p func %p arg %p",
  705                             c, c_func, c_arg);
  706                 }
  707         } else {
  708 #ifdef CALLOUT_PROFILING
  709                 (*mpcalls)++;
  710 #endif
  711                 CTR3(KTR_CALLOUT, "callout %p func %p arg %p",
  712                     c, c_func, c_arg);
  713         }
  714 #if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING)
  715         sbt1 = sbinuptime();
  716 #endif
  717         THREAD_NO_SLEEPING();
  718         SDT_PROBE(callout_execute, kernel, , callout__start, c, 0, 0, 0, 0);
  719         c_func(c_arg);
  720         SDT_PROBE(callout_execute, kernel, , callout__end, c, 0, 0, 0, 0);
  721         THREAD_SLEEPING_OK();
  722 #if defined(DIAGNOSTIC) || defined(CALLOUT_PROFILING)
  723         sbt2 = sbinuptime();
  724         sbt2 -= sbt1;
  725         if (sbt2 > maxdt) {
  726                 if (lastfunc != c_func || sbt2 > maxdt * 2) {
  727                         ts2 = sbttots(sbt2);
  728                         printf(
  729                 "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  730                             c_func, c_arg, (intmax_t)ts2.tv_sec, ts2.tv_nsec);
  731                 }
  732                 maxdt = sbt2;
  733                 lastfunc = c_func;
  734         }
  735 #endif
  736         CTR1(KTR_CALLOUT, "callout %p finished", c);
  737         if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
  738                 class->lc_unlock(c_lock);
  739 skip:
  740         CC_LOCK(cc);
  741         KASSERT(cc->cc_exec_entity[direct].cc_curr == c, ("mishandled cc_curr"));
  742         cc->cc_exec_entity[direct].cc_curr = NULL;
  743         if (cc->cc_exec_entity[direct].cc_waiting) {
  744                 /*
  745                  * There is someone waiting for the
  746                  * callout to complete.
  747                  * If the callout was scheduled for
  748                  * migration just cancel it.
  749                  */
  750                 if (cc_cce_migrating(cc, direct)) {
  751                         cc_cce_cleanup(cc, direct);
  752 
  753                         /*
  754                          * It should be assert here that the callout is not
  755                          * destroyed but that is not easy.
  756                          */
  757                         c->c_flags &= ~CALLOUT_DFRMIGRATION;
  758                 }
  759                 cc->cc_exec_entity[direct].cc_waiting = false;
  760                 CC_UNLOCK(cc);
  761                 wakeup(&cc->cc_exec_entity[direct].cc_waiting);
  762                 CC_LOCK(cc);
  763         } else if (cc_cce_migrating(cc, direct)) {
  764                 KASSERT((c_flags & CALLOUT_LOCAL_ALLOC) == 0,
  765                     ("Migrating legacy callout %p", c));
  766 #ifdef SMP
  767                 /*
  768                  * If the callout was scheduled for
  769                  * migration just perform it now.
  770                  */
  771                 new_cpu = cc->cc_exec_entity[direct].ce_migration_cpu;
  772                 new_time = cc->cc_exec_entity[direct].ce_migration_time;
  773                 new_prec = cc->cc_exec_entity[direct].ce_migration_prec;
  774                 new_func = cc->cc_exec_entity[direct].ce_migration_func;
  775                 new_arg = cc->cc_exec_entity[direct].ce_migration_arg;
  776                 cc_cce_cleanup(cc, direct);
  777 
  778                 /*
  779                  * It should be assert here that the callout is not destroyed
  780                  * but that is not easy.
  781                  *
  782                  * As first thing, handle deferred callout stops.
  783                  */
  784                 if ((c->c_flags & CALLOUT_DFRMIGRATION) == 0) {
  785                         CTR3(KTR_CALLOUT,
  786                              "deferred cancelled %p func %p arg %p",
  787                              c, new_func, new_arg);
  788                         callout_cc_del(c, cc);
  789                         return;
  790                 }
  791                 c->c_flags &= ~CALLOUT_DFRMIGRATION;
  792 
  793                 new_cc = callout_cpu_switch(c, cc, new_cpu);
  794                 flags = (direct) ? C_DIRECT_EXEC : 0;
  795                 callout_cc_add(c, new_cc, new_time, new_prec, new_func,
  796                     new_arg, new_cpu, flags);
  797                 CC_UNLOCK(new_cc);
  798                 CC_LOCK(cc);
  799 #else
  800                 panic("migration should not happen");
  801 #endif
  802         }
  803         /*
  804          * If the current callout is locally allocated (from
  805          * timeout(9)) then put it on the freelist.
  806          *
  807          * Note: we need to check the cached copy of c_flags because
  808          * if it was not local, then it's not safe to deref the
  809          * callout pointer.
  810          */
  811         KASSERT((c_flags & CALLOUT_LOCAL_ALLOC) == 0 ||
  812             c->c_flags == CALLOUT_LOCAL_ALLOC,
  813             ("corrupted callout"));
  814         if (c_flags & CALLOUT_LOCAL_ALLOC)
  815                 callout_cc_del(c, cc);
  816 }
  817 
  818 /*
  819  * The callout mechanism is based on the work of Adam M. Costello and
  820  * George Varghese, published in a technical report entitled "Redesigning
  821  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  822  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  823  * used in this implementation was published by G. Varghese and T. Lauck in
  824  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  825  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  826  * the 11th ACM Annual Symposium on Operating Systems Principles,
  827  * Austin, Texas Nov 1987.
  828  */
  829 
  830 /*
  831  * Software (low priority) clock interrupt.
  832  * Run periodic events from timeout queue.
  833  */
  834 void
  835 softclock(void *arg)
  836 {
  837         struct callout_cpu *cc;
  838         struct callout *c;
  839 #ifdef CALLOUT_PROFILING
  840         int depth = 0, gcalls = 0, lockcalls = 0, mpcalls = 0;
  841 #endif
  842 
  843         cc = (struct callout_cpu *)arg;
  844         CC_LOCK(cc);
  845         while ((c = TAILQ_FIRST(&cc->cc_expireq)) != NULL) {
  846                 TAILQ_REMOVE(&cc->cc_expireq, c, c_links.tqe);
  847                 softclock_call_cc(c, cc,
  848 #ifdef CALLOUT_PROFILING
  849                     &mpcalls, &lockcalls, &gcalls,
  850 #endif
  851                     0);
  852 #ifdef CALLOUT_PROFILING
  853                 ++depth;
  854 #endif
  855         }
  856 #ifdef CALLOUT_PROFILING
  857         avg_depth += (depth * 1000 - avg_depth) >> 8;
  858         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  859         avg_lockcalls += (lockcalls * 1000 - avg_lockcalls) >> 8;
  860         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  861 #endif
  862         CC_UNLOCK(cc);
  863 }
  864 
  865 /*
  866  * timeout --
  867  *      Execute a function after a specified length of time.
  868  *
  869  * untimeout --
  870  *      Cancel previous timeout function call.
  871  *
  872  * callout_handle_init --
  873  *      Initialize a handle so that using it with untimeout is benign.
  874  *
  875  *      See AT&T BCI Driver Reference Manual for specification.  This
  876  *      implementation differs from that one in that although an
  877  *      identification value is returned from timeout, the original
  878  *      arguments to timeout as well as the identifier are used to
  879  *      identify entries for untimeout.
  880  */
  881 struct callout_handle
  882 timeout(timeout_t *ftn, void *arg, int to_ticks)
  883 {
  884         struct callout_cpu *cc;
  885         struct callout *new;
  886         struct callout_handle handle;
  887 
  888         cc = CC_CPU(timeout_cpu);
  889         CC_LOCK(cc);
  890         /* Fill in the next free callout structure. */
  891         new = SLIST_FIRST(&cc->cc_callfree);
  892         if (new == NULL)
  893                 /* XXX Attempt to malloc first */
  894                 panic("timeout table full");
  895         SLIST_REMOVE_HEAD(&cc->cc_callfree, c_links.sle);
  896         callout_reset(new, to_ticks, ftn, arg);
  897         handle.callout = new;
  898         CC_UNLOCK(cc);
  899 
  900         return (handle);
  901 }
  902 
  903 void
  904 untimeout(timeout_t *ftn, void *arg, struct callout_handle handle)
  905 {
  906         struct callout_cpu *cc;
  907 
  908         /*
  909          * Check for a handle that was initialized
  910          * by callout_handle_init, but never used
  911          * for a real timeout.
  912          */
  913         if (handle.callout == NULL)
  914                 return;
  915 
  916         cc = callout_lock(handle.callout);
  917         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  918                 callout_stop(handle.callout);
  919         CC_UNLOCK(cc);
  920 }
  921 
  922 void
  923 callout_handle_init(struct callout_handle *handle)
  924 {
  925         handle->callout = NULL;
  926 }
  927 
  928 /*
  929  * New interface; clients allocate their own callout structures.
  930  *
  931  * callout_reset() - establish or change a timeout
  932  * callout_stop() - disestablish a timeout
  933  * callout_init() - initialize a callout structure so that it can
  934  *      safely be passed to callout_reset() and callout_stop()
  935  *
  936  * <sys/callout.h> defines three convenience macros:
  937  *
  938  * callout_active() - returns truth if callout has not been stopped,
  939  *      drained, or deactivated since the last time the callout was
  940  *      reset.
  941  * callout_pending() - returns truth if callout is still waiting for timeout
  942  * callout_deactivate() - marks the callout as having been serviced
  943  */
  944 int
  945 callout_reset_sbt_on(struct callout *c, sbintime_t sbt, sbintime_t precision,
  946     void (*ftn)(void *), void *arg, int cpu, int flags)
  947 {
  948         sbintime_t to_sbt, pr;
  949         struct callout_cpu *cc;
  950         int cancelled, direct;
  951 
  952         cancelled = 0;
  953         if (flags & C_ABSOLUTE) {
  954                 to_sbt = sbt;
  955         } else {
  956                 if ((flags & C_HARDCLOCK) && (sbt < tick_sbt))
  957                         sbt = tick_sbt;
  958                 if ((flags & C_HARDCLOCK) ||
  959 #ifdef NO_EVENTTIMERS
  960                     sbt >= sbt_timethreshold) {
  961                         to_sbt = getsbinuptime();
  962 
  963                         /* Add safety belt for the case of hz > 1000. */
  964                         to_sbt += tc_tick_sbt - tick_sbt;
  965 #else
  966                     sbt >= sbt_tickthreshold) {
  967                         /*
  968                          * Obtain the time of the last hardclock() call on
  969                          * this CPU directly from the kern_clocksource.c.
  970                          * This value is per-CPU, but it is equal for all
  971                          * active ones.
  972                          */
  973 #ifdef __LP64__
  974                         to_sbt = DPCPU_GET(hardclocktime);
  975 #else
  976                         spinlock_enter();
  977                         to_sbt = DPCPU_GET(hardclocktime);
  978                         spinlock_exit();
  979 #endif
  980 #endif
  981                         if ((flags & C_HARDCLOCK) == 0)
  982                                 to_sbt += tick_sbt;
  983                 } else
  984                         to_sbt = sbinuptime();
  985                 if (SBT_MAX - to_sbt < sbt)
  986                         to_sbt = SBT_MAX;
  987                 else
  988                         to_sbt += sbt;
  989                 pr = ((C_PRELGET(flags) < 0) ? sbt >> tc_precexp :
  990                     sbt >> C_PRELGET(flags));
  991                 if (pr > precision)
  992                         precision = pr;
  993         }
  994         /*
  995          * Don't allow migration of pre-allocated callouts lest they
  996          * become unbalanced.
  997          */
  998         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  999                 cpu = c->c_cpu;
 1000         direct = (c->c_flags & CALLOUT_DIRECT) != 0;
 1001         KASSERT(!direct || c->c_lock == NULL,
 1002             ("%s: direct callout %p has lock", __func__, c));
 1003         cc = callout_lock(c);
 1004         if (cc->cc_exec_entity[direct].cc_curr == c) {
 1005                 /*
 1006                  * We're being asked to reschedule a callout which is
 1007                  * currently in progress.  If there is a lock then we
 1008                  * can cancel the callout if it has not really started.
 1009                  */
 1010                 if (c->c_lock != NULL && !cc->cc_exec_entity[direct].cc_cancel)
 1011                         cancelled = cc->cc_exec_entity[direct].cc_cancel = true;
 1012                 if (cc->cc_exec_entity[direct].cc_waiting) {
 1013                         /*
 1014                          * Someone has called callout_drain to kill this
 1015                          * callout.  Don't reschedule.
 1016                          */
 1017                         CTR4(KTR_CALLOUT, "%s %p func %p arg %p",
 1018                             cancelled ? "cancelled" : "failed to cancel",
 1019                             c, c->c_func, c->c_arg);
 1020                         CC_UNLOCK(cc);
 1021                         return (cancelled);
 1022                 }
 1023         }
 1024         if (c->c_flags & CALLOUT_PENDING) {
 1025                 if ((c->c_flags & CALLOUT_PROCESSED) == 0) {
 1026                         if (cc->cc_exec_next_dir == c)
 1027                                 cc->cc_exec_next_dir = LIST_NEXT(c, c_links.le);
 1028                         LIST_REMOVE(c, c_links.le);
 1029                 } else
 1030                         TAILQ_REMOVE(&cc->cc_expireq, c, c_links.tqe);
 1031                 cancelled = 1;
 1032                 c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
 1033         }
 1034 
 1035 #ifdef SMP
 1036         /*
 1037          * If the callout must migrate try to perform it immediately.
 1038          * If the callout is currently running, just defer the migration
 1039          * to a more appropriate moment.
 1040          */
 1041         if (c->c_cpu != cpu) {
 1042                 if (cc->cc_exec_entity[direct].cc_curr == c) {
 1043                         cc->cc_exec_entity[direct].ce_migration_cpu = cpu;
 1044                         cc->cc_exec_entity[direct].ce_migration_time
 1045                             = to_sbt;
 1046                         cc->cc_exec_entity[direct].ce_migration_prec 
 1047                             = precision;
 1048                         cc->cc_exec_entity[direct].ce_migration_func = ftn;
 1049                         cc->cc_exec_entity[direct].ce_migration_arg = arg;
 1050                         c->c_flags |= CALLOUT_DFRMIGRATION;
 1051                         CTR6(KTR_CALLOUT,
 1052                     "migration of %p func %p arg %p in %d.%08x to %u deferred",
 1053                             c, c->c_func, c->c_arg, (int)(to_sbt >> 32),
 1054                             (u_int)(to_sbt & 0xffffffff), cpu);
 1055                         CC_UNLOCK(cc);
 1056                         return (cancelled);
 1057                 }
 1058                 cc = callout_cpu_switch(c, cc, cpu);
 1059         }
 1060 #endif
 1061 
 1062         callout_cc_add(c, cc, to_sbt, precision, ftn, arg, cpu, flags);
 1063         CTR6(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d.%08x",
 1064             cancelled ? "re" : "", c, c->c_func, c->c_arg, (int)(to_sbt >> 32),
 1065             (u_int)(to_sbt & 0xffffffff));
 1066         CC_UNLOCK(cc);
 1067 
 1068         return (cancelled);
 1069 }
 1070 
 1071 /*
 1072  * Common idioms that can be optimized in the future.
 1073  */
 1074 int
 1075 callout_schedule_on(struct callout *c, int to_ticks, int cpu)
 1076 {
 1077         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, cpu);
 1078 }
 1079 
 1080 int
 1081 callout_schedule(struct callout *c, int to_ticks)
 1082 {
 1083         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, c->c_cpu);
 1084 }
 1085 
 1086 int
 1087 _callout_stop_safe(struct callout *c, int safe)
 1088 {
 1089         struct callout_cpu *cc, *old_cc;
 1090         struct lock_class *class;
 1091         int direct, sq_locked, use_lock;
 1092 
 1093         /*
 1094          * Some old subsystems don't hold Giant while running a callout_stop(),
 1095          * so just discard this check for the moment.
 1096          */
 1097         if (!safe && c->c_lock != NULL) {
 1098                 if (c->c_lock == &Giant.lock_object)
 1099                         use_lock = mtx_owned(&Giant);
 1100                 else {
 1101                         use_lock = 1;
 1102                         class = LOCK_CLASS(c->c_lock);
 1103                         class->lc_assert(c->c_lock, LA_XLOCKED);
 1104                 }
 1105         } else
 1106                 use_lock = 0;
 1107         direct = (c->c_flags & CALLOUT_DIRECT) != 0;
 1108         sq_locked = 0;
 1109         old_cc = NULL;
 1110 again:
 1111         cc = callout_lock(c);
 1112 
 1113         /*
 1114          * If the callout was migrating while the callout cpu lock was
 1115          * dropped,  just drop the sleepqueue lock and check the states
 1116          * again.
 1117          */
 1118         if (sq_locked != 0 && cc != old_cc) {
 1119 #ifdef SMP
 1120                 CC_UNLOCK(cc);
 1121                 sleepq_release(&old_cc->cc_exec_entity[direct].cc_waiting);
 1122                 sq_locked = 0;
 1123                 old_cc = NULL;
 1124                 goto again;
 1125 #else
 1126                 panic("migration should not happen");
 1127 #endif
 1128         }
 1129 
 1130         /*
 1131          * If the callout isn't pending, it's not on the queue, so
 1132          * don't attempt to remove it from the queue.  We can try to
 1133          * stop it by other means however.
 1134          */
 1135         if (!(c->c_flags & CALLOUT_PENDING)) {
 1136                 c->c_flags &= ~CALLOUT_ACTIVE;
 1137 
 1138                 /*
 1139                  * If it wasn't on the queue and it isn't the current
 1140                  * callout, then we can't stop it, so just bail.
 1141                  */
 1142                 if (cc->cc_exec_entity[direct].cc_curr != c) {
 1143                         CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
 1144                             c, c->c_func, c->c_arg);
 1145                         CC_UNLOCK(cc);
 1146                         if (sq_locked)
 1147                                 sleepq_release(
 1148                                     &cc->cc_exec_entity[direct].cc_waiting);
 1149                         return (0);
 1150                 }
 1151 
 1152                 if (safe) {
 1153                         /*
 1154                          * The current callout is running (or just
 1155                          * about to run) and blocking is allowed, so
 1156                          * just wait for the current invocation to
 1157                          * finish.
 1158                          */
 1159                         while (cc->cc_exec_entity[direct].cc_curr == c) {
 1160                                 /*
 1161                                  * Use direct calls to sleepqueue interface
 1162                                  * instead of cv/msleep in order to avoid
 1163                                  * a LOR between cc_lock and sleepqueue
 1164                                  * chain spinlocks.  This piece of code
 1165                                  * emulates a msleep_spin() call actually.
 1166                                  *
 1167                                  * If we already have the sleepqueue chain
 1168                                  * locked, then we can safely block.  If we
 1169                                  * don't already have it locked, however,
 1170                                  * we have to drop the cc_lock to lock
 1171                                  * it.  This opens several races, so we
 1172                                  * restart at the beginning once we have
 1173                                  * both locks.  If nothing has changed, then
 1174                                  * we will end up back here with sq_locked
 1175                                  * set.
 1176                                  */
 1177                                 if (!sq_locked) {
 1178                                         CC_UNLOCK(cc);
 1179                                         sleepq_lock(
 1180                                         &cc->cc_exec_entity[direct].cc_waiting);
 1181                                         sq_locked = 1;
 1182                                         old_cc = cc;
 1183                                         goto again;
 1184                                 }
 1185 
 1186                                 /*
 1187                                  * Migration could be cancelled here, but
 1188                                  * as long as it is still not sure when it
 1189                                  * will be packed up, just let softclock()
 1190                                  * take care of it.
 1191                                  */
 1192                                 cc->cc_exec_entity[direct].cc_waiting = true;
 1193                                 DROP_GIANT();
 1194                                 CC_UNLOCK(cc);
 1195                                 sleepq_add(
 1196                                     &cc->cc_exec_entity[direct].cc_waiting,
 1197                                     &cc->cc_lock.lock_object, "codrain",
 1198                                     SLEEPQ_SLEEP, 0);
 1199                                 sleepq_wait(
 1200                                     &cc->cc_exec_entity[direct].cc_waiting,
 1201                                              0);
 1202                                 sq_locked = 0;
 1203                                 old_cc = NULL;
 1204 
 1205                                 /* Reacquire locks previously released. */
 1206                                 PICKUP_GIANT();
 1207                                 CC_LOCK(cc);
 1208                         }
 1209                 } else if (use_lock &&
 1210                             !cc->cc_exec_entity[direct].cc_cancel) {
 1211                         /*
 1212                          * The current callout is waiting for its
 1213                          * lock which we hold.  Cancel the callout
 1214                          * and return.  After our caller drops the
 1215                          * lock, the callout will be skipped in
 1216                          * softclock().
 1217                          */
 1218                         cc->cc_exec_entity[direct].cc_cancel = true;
 1219                         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
 1220                             c, c->c_func, c->c_arg);
 1221                         KASSERT(!cc_cce_migrating(cc, direct),
 1222                             ("callout wrongly scheduled for migration"));
 1223                         CC_UNLOCK(cc);
 1224                         KASSERT(!sq_locked, ("sleepqueue chain locked"));
 1225                         return (1);
 1226                 } else if ((c->c_flags & CALLOUT_DFRMIGRATION) != 0) {
 1227                         c->c_flags &= ~CALLOUT_DFRMIGRATION;
 1228                         CTR3(KTR_CALLOUT, "postponing stop %p func %p arg %p",
 1229                             c, c->c_func, c->c_arg);
 1230                         CC_UNLOCK(cc);
 1231                         return (1);
 1232                 }
 1233                 CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
 1234                     c, c->c_func, c->c_arg);
 1235                 CC_UNLOCK(cc);
 1236                 KASSERT(!sq_locked, ("sleepqueue chain still locked"));
 1237                 return (0);
 1238         }
 1239         if (sq_locked)
 1240                 sleepq_release(&cc->cc_exec_entity[direct].cc_waiting);
 1241 
 1242         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
 1243 
 1244         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
 1245             c, c->c_func, c->c_arg);
 1246         if ((c->c_flags & CALLOUT_PROCESSED) == 0) {
 1247                 if (cc->cc_exec_next_dir == c)
 1248                         cc->cc_exec_next_dir = LIST_NEXT(c, c_links.le);
 1249                 LIST_REMOVE(c, c_links.le);
 1250         } else
 1251                 TAILQ_REMOVE(&cc->cc_expireq, c, c_links.tqe);
 1252         callout_cc_del(c, cc);
 1253 
 1254         CC_UNLOCK(cc);
 1255         return (1);
 1256 }
 1257 
 1258 void
 1259 callout_init(struct callout *c, int mpsafe)
 1260 {
 1261         bzero(c, sizeof *c);
 1262         if (mpsafe) {
 1263                 c->c_lock = NULL;
 1264                 c->c_flags = CALLOUT_RETURNUNLOCKED;
 1265         } else {
 1266                 c->c_lock = &Giant.lock_object;
 1267                 c->c_flags = 0;
 1268         }
 1269         c->c_cpu = timeout_cpu;
 1270 }
 1271 
 1272 void
 1273 _callout_init_lock(struct callout *c, struct lock_object *lock, int flags)
 1274 {
 1275         bzero(c, sizeof *c);
 1276         c->c_lock = lock;
 1277         KASSERT((flags & ~(CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK)) == 0,
 1278             ("callout_init_lock: bad flags %d", flags));
 1279         KASSERT(lock != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
 1280             ("callout_init_lock: CALLOUT_RETURNUNLOCKED with no lock"));
 1281         KASSERT(lock == NULL || !(LOCK_CLASS(lock)->lc_flags &
 1282             (LC_SPINLOCK | LC_SLEEPABLE)), ("%s: invalid lock class",
 1283             __func__));
 1284         c->c_flags = flags & (CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK);
 1285         c->c_cpu = timeout_cpu;
 1286 }
 1287 
 1288 #ifdef APM_FIXUP_CALLTODO
 1289 /* 
 1290  * Adjust the kernel calltodo timeout list.  This routine is used after 
 1291  * an APM resume to recalculate the calltodo timer list values with the 
 1292  * number of hz's we have been sleeping.  The next hardclock() will detect 
 1293  * that there are fired timers and run softclock() to execute them.
 1294  *
 1295  * Please note, I have not done an exhaustive analysis of what code this
 1296  * might break.  I am motivated to have my select()'s and alarm()'s that
 1297  * have expired during suspend firing upon resume so that the applications
 1298  * which set the timer can do the maintanence the timer was for as close
 1299  * as possible to the originally intended time.  Testing this code for a 
 1300  * week showed that resuming from a suspend resulted in 22 to 25 timers 
 1301  * firing, which seemed independant on whether the suspend was 2 hours or
 1302  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
 1303  */
 1304 void
 1305 adjust_timeout_calltodo(struct timeval *time_change)
 1306 {
 1307         register struct callout *p;
 1308         unsigned long delta_ticks;
 1309 
 1310         /* 
 1311          * How many ticks were we asleep?
 1312          * (stolen from tvtohz()).
 1313          */
 1314 
 1315         /* Don't do anything */
 1316         if (time_change->tv_sec < 0)
 1317                 return;
 1318         else if (time_change->tv_sec <= LONG_MAX / 1000000)
 1319                 delta_ticks = (time_change->tv_sec * 1000000 +
 1320                                time_change->tv_usec + (tick - 1)) / tick + 1;
 1321         else if (time_change->tv_sec <= LONG_MAX / hz)
 1322                 delta_ticks = time_change->tv_sec * hz +
 1323                               (time_change->tv_usec + (tick - 1)) / tick + 1;
 1324         else
 1325                 delta_ticks = LONG_MAX;
 1326 
 1327         if (delta_ticks > INT_MAX)
 1328                 delta_ticks = INT_MAX;
 1329 
 1330         /* 
 1331          * Now rip through the timer calltodo list looking for timers
 1332          * to expire.
 1333          */
 1334 
 1335         /* don't collide with softclock() */
 1336         CC_LOCK(cc);
 1337         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
 1338                 p->c_time -= delta_ticks;
 1339 
 1340                 /* Break if the timer had more time on it than delta_ticks */
 1341                 if (p->c_time > 0)
 1342                         break;
 1343 
 1344                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
 1345                 delta_ticks = -p->c_time;
 1346         }
 1347         CC_UNLOCK(cc);
 1348 
 1349         return;
 1350 }
 1351 #endif /* APM_FIXUP_CALLTODO */
 1352 
 1353 static int
 1354 flssbt(sbintime_t sbt)
 1355 {
 1356 
 1357         sbt += (uint64_t)sbt >> 1;
 1358         if (sizeof(long) >= sizeof(sbintime_t))
 1359                 return (flsl(sbt));
 1360         if (sbt >= SBT_1S)
 1361                 return (flsl(((uint64_t)sbt) >> 32) + 32);
 1362         return (flsl(sbt));
 1363 }
 1364 
 1365 /*
 1366  * Dump immediate statistic snapshot of the scheduled callouts.
 1367  */
 1368 static int
 1369 sysctl_kern_callout_stat(SYSCTL_HANDLER_ARGS)
 1370 {
 1371         struct callout *tmp;
 1372         struct callout_cpu *cc;
 1373         struct callout_list *sc;
 1374         sbintime_t maxpr, maxt, medpr, medt, now, spr, st, t;
 1375         int ct[64], cpr[64], ccpbk[32];
 1376         int error, val, i, count, tcum, pcum, maxc, c, medc;
 1377 #ifdef SMP
 1378         int cpu;
 1379 #endif
 1380 
 1381         val = 0;
 1382         error = sysctl_handle_int(oidp, &val, 0, req);
 1383         if (error != 0 || req->newptr == NULL)
 1384                 return (error);
 1385         count = maxc = 0;
 1386         st = spr = maxt = maxpr = 0;
 1387         bzero(ccpbk, sizeof(ccpbk));
 1388         bzero(ct, sizeof(ct));
 1389         bzero(cpr, sizeof(cpr));
 1390         now = sbinuptime();
 1391 #ifdef SMP
 1392         CPU_FOREACH(cpu) {
 1393                 cc = CC_CPU(cpu);
 1394 #else
 1395                 cc = CC_CPU(timeout_cpu);
 1396 #endif
 1397                 CC_LOCK(cc);
 1398                 for (i = 0; i < callwheelsize; i++) {
 1399                         sc = &cc->cc_callwheel[i];
 1400                         c = 0;
 1401                         LIST_FOREACH(tmp, sc, c_links.le) {
 1402                                 c++;
 1403                                 t = tmp->c_time - now;
 1404                                 if (t < 0)
 1405                                         t = 0;
 1406                                 st += t / SBT_1US;
 1407                                 spr += tmp->c_precision / SBT_1US;
 1408                                 if (t > maxt)
 1409                                         maxt = t;
 1410                                 if (tmp->c_precision > maxpr)
 1411                                         maxpr = tmp->c_precision;
 1412                                 ct[flssbt(t)]++;
 1413                                 cpr[flssbt(tmp->c_precision)]++;
 1414                         }
 1415                         if (c > maxc)
 1416                                 maxc = c;
 1417                         ccpbk[fls(c + c / 2)]++;
 1418                         count += c;
 1419                 }
 1420                 CC_UNLOCK(cc);
 1421 #ifdef SMP
 1422         }
 1423 #endif
 1424 
 1425         for (i = 0, tcum = 0; i < 64 && tcum < count / 2; i++)
 1426                 tcum += ct[i];
 1427         medt = (i >= 2) ? (((sbintime_t)1) << (i - 2)) : 0;
 1428         for (i = 0, pcum = 0; i < 64 && pcum < count / 2; i++)
 1429                 pcum += cpr[i];
 1430         medpr = (i >= 2) ? (((sbintime_t)1) << (i - 2)) : 0;
 1431         for (i = 0, c = 0; i < 32 && c < count / 2; i++)
 1432                 c += ccpbk[i];
 1433         medc = (i >= 2) ? (1 << (i - 2)) : 0;
 1434 
 1435         printf("Scheduled callouts statistic snapshot:\n");
 1436         printf("  Callouts: %6d  Buckets: %6d*%-3d  Bucket size: 0.%06ds\n",
 1437             count, callwheelsize, mp_ncpus, 1000000 >> CC_HASH_SHIFT);
 1438         printf("  C/Bk: med %5d         avg %6d.%06jd  max %6d\n",
 1439             medc,
 1440             count / callwheelsize / mp_ncpus,
 1441             (uint64_t)count * 1000000 / callwheelsize / mp_ncpus % 1000000,
 1442             maxc);
 1443         printf("  Time: med %5jd.%06jds avg %6jd.%06jds max %6jd.%06jds\n",
 1444             medt / SBT_1S, (medt & 0xffffffff) * 1000000 >> 32,
 1445             (st / count) / 1000000, (st / count) % 1000000,
 1446             maxt / SBT_1S, (maxt & 0xffffffff) * 1000000 >> 32);
 1447         printf("  Prec: med %5jd.%06jds avg %6jd.%06jds max %6jd.%06jds\n",
 1448             medpr / SBT_1S, (medpr & 0xffffffff) * 1000000 >> 32,
 1449             (spr / count) / 1000000, (spr / count) % 1000000,
 1450             maxpr / SBT_1S, (maxpr & 0xffffffff) * 1000000 >> 32);
 1451         printf("  Distribution:       \tbuckets\t   time\t   tcum\t"
 1452             "   prec\t   pcum\n");
 1453         for (i = 0, tcum = pcum = 0; i < 64; i++) {
 1454                 if (ct[i] == 0 && cpr[i] == 0)
 1455                         continue;
 1456                 t = (i != 0) ? (((sbintime_t)1) << (i - 1)) : 0;
 1457                 tcum += ct[i];
 1458                 pcum += cpr[i];
 1459                 printf("  %10jd.%06jds\t 2**%d\t%7d\t%7d\t%7d\t%7d\n",
 1460                     t / SBT_1S, (t & 0xffffffff) * 1000000 >> 32,
 1461                     i - 1 - (32 - CC_HASH_SHIFT),
 1462                     ct[i], tcum, cpr[i], pcum);
 1463         }
 1464         return (error);
 1465 }
 1466 SYSCTL_PROC(_kern, OID_AUTO, callout_stat,
 1467     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
 1468     0, 0, sysctl_kern_callout_stat, "I",
 1469     "Dump immediate statistic snapshot of the scheduled callouts");

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