kern_tc.c

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    1 /* $NetBSD: kern_tc.c,v 1.62 2021/06/02 21:34:58 riastradh Exp $ */
    2 
    3 /*-
    4  * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Andrew Doran.
    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  *
   19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   29  * POSSIBILITY OF SUCH DAMAGE.
   30  */
   31 
   32 /*-
   33  * ----------------------------------------------------------------------------
   34  * "THE BEER-WARE LICENSE" (Revision 42):
   35  * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
   36  * can do whatever you want with this stuff. If we meet some day, and you think
   37  * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
   38  * ---------------------------------------------------------------------------
   39  */
   40 
   41 #include <sys/cdefs.h>
   42 /* __FBSDID("$FreeBSD: src/sys/kern/kern_tc.c,v 1.166 2005/09/19 22:16:31 andre Exp $"); */
   43 __KERNEL_RCSID(0, "$NetBSD: kern_tc.c,v 1.62 2021/06/02 21:34:58 riastradh Exp $");
   44 
   45 #ifdef _KERNEL_OPT
   46 #include "opt_ntp.h"
   47 #endif
   48 
   49 #include <sys/param.h>
   50 #include <sys/atomic.h>
   51 #include <sys/evcnt.h>
   52 #include <sys/kauth.h>
   53 #include <sys/kernel.h>
   54 #include <sys/mutex.h>
   55 #include <sys/reboot.h> /* XXX just to get AB_VERBOSE */
   56 #include <sys/sysctl.h>
   57 #include <sys/syslog.h>
   58 #include <sys/systm.h>
   59 #include <sys/timepps.h>
   60 #include <sys/timetc.h>
   61 #include <sys/timex.h>
   62 #include <sys/xcall.h>
   63 
   64 /*
   65  * A large step happens on boot.  This constant detects such steps.
   66  * It is relatively small so that ntp_update_second gets called enough
   67  * in the typical 'missed a couple of seconds' case, but doesn't loop
   68  * forever when the time step is large.
   69  */
   70 #define LARGE_STEP      200
   71 
   72 /*
   73  * Implement a dummy timecounter which we can use until we get a real one
   74  * in the air.  This allows the console and other early stuff to use
   75  * time services.
   76  */
   77 
   78 static u_int
   79 dummy_get_timecount(struct timecounter *tc)
   80 {
   81         static u_int now;
   82 
   83         return ++now;
   84 }
   85 
   86 static struct timecounter dummy_timecounter = {
   87         .tc_get_timecount       = dummy_get_timecount,
   88         .tc_counter_mask        = ~0u,
   89         .tc_frequency           = 1000000,
   90         .tc_name                = "dummy",
   91         .tc_quality             = -1000000,
   92         .tc_priv                = NULL,
   93 };
   94 
   95 struct timehands {
   96         /* These fields must be initialized by the driver. */
   97         struct timecounter      *th_counter;     /* active timecounter */
   98         int64_t                 th_adjustment;   /* frequency adjustment */
   99                                                  /* (NTP/adjtime) */
  100         uint64_t                th_scale;        /* scale factor (counter */
  101                                                  /* tick->time) */
  102         uint64_t                th_offset_count; /* offset at last time */
  103                                                  /* update (tc_windup()) */
  104         struct bintime          th_offset;       /* bin (up)time at windup */
  105         struct timeval          th_microtime;    /* cached microtime */
  106         struct timespec         th_nanotime;     /* cached nanotime */
  107         /* Fields not to be copied in tc_windup start with th_generation. */
  108         volatile u_int          th_generation;   /* current genration */
  109         struct timehands        *th_next;        /* next timehand */
  110 };
  111 
  112 static struct timehands th0;
  113 static struct timehands th9 = { .th_next = &th0, };
  114 static struct timehands th8 = { .th_next = &th9, };
  115 static struct timehands th7 = { .th_next = &th8, };
  116 static struct timehands th6 = { .th_next = &th7, };
  117 static struct timehands th5 = { .th_next = &th6, };
  118 static struct timehands th4 = { .th_next = &th5, };
  119 static struct timehands th3 = { .th_next = &th4, };
  120 static struct timehands th2 = { .th_next = &th3, };
  121 static struct timehands th1 = { .th_next = &th2, };
  122 static struct timehands th0 = {
  123         .th_counter = &dummy_timecounter,
  124         .th_scale = (uint64_t)-1 / 1000000,
  125         .th_offset = { .sec = 1, .frac = 0 },
  126         .th_generation = 1,
  127         .th_next = &th1,
  128 };
  129 
  130 static struct timehands *volatile timehands = &th0;
  131 struct timecounter *timecounter = &dummy_timecounter;
  132 static struct timecounter *timecounters = &dummy_timecounter;
  133 
  134 volatile time_t time_second __cacheline_aligned = 1;
  135 volatile time_t time_uptime __cacheline_aligned = 1;
  136 
  137 static struct bintime timebasebin;
  138 
  139 static int timestepwarnings;
  140 
  141 kmutex_t timecounter_lock;
  142 static u_int timecounter_mods;
  143 static volatile int timecounter_removals = 1;
  144 static u_int timecounter_bad;
  145 
  146 /*
  147  * sysctl helper routine for kern.timercounter.hardware
  148  */
  149 static int
  150 sysctl_kern_timecounter_hardware(SYSCTLFN_ARGS)
  151 {
  152         struct sysctlnode node;
  153         int error;
  154         char newname[MAX_TCNAMELEN];
  155         struct timecounter *newtc, *tc;
  156 
  157         tc = timecounter;
  158 
  159         strlcpy(newname, tc->tc_name, sizeof(newname));
  160 
  161         node = *rnode;
  162         node.sysctl_data = newname;
  163         node.sysctl_size = sizeof(newname);
  164 
  165         error = sysctl_lookup(SYSCTLFN_CALL(&node));
  166 
  167         if (error ||
  168             newp == NULL ||
  169             strncmp(newname, tc->tc_name, sizeof(newname)) == 0)
  170                 return error;
  171 
  172         if (l != NULL && (error = kauth_authorize_system(l->l_cred, 
  173             KAUTH_SYSTEM_TIME, KAUTH_REQ_SYSTEM_TIME_TIMECOUNTERS, newname,
  174             NULL, NULL)) != 0)
  175                 return error;
  176 
  177         if (!cold)
  178                 mutex_spin_enter(&timecounter_lock);
  179         error = EINVAL;
  180         for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) {
  181                 if (strcmp(newname, newtc->tc_name) != 0)
  182                         continue;
  183                 /* Warm up new timecounter. */
  184                 (void)newtc->tc_get_timecount(newtc);
  185                 (void)newtc->tc_get_timecount(newtc);
  186                 timecounter = newtc;
  187                 error = 0;
  188                 break;
  189         }
  190         if (!cold)
  191                 mutex_spin_exit(&timecounter_lock);
  192         return error;
  193 }
  194 
  195 static int
  196 sysctl_kern_timecounter_choice(SYSCTLFN_ARGS)
  197 {
  198         char buf[MAX_TCNAMELEN+48];
  199         char *where;
  200         const char *spc;
  201         struct timecounter *tc;
  202         size_t needed, left, slen;
  203         int error, mods;
  204 
  205         if (newp != NULL)
  206                 return EPERM;
  207         if (namelen != 0)
  208                 return EINVAL;
  209 
  210         mutex_spin_enter(&timecounter_lock);
  211  retry:
  212         spc = "";
  213         error = 0;
  214         needed = 0;
  215         left = *oldlenp;
  216         where = oldp;
  217         for (tc = timecounters; error == 0 && tc != NULL; tc = tc->tc_next) {
  218                 if (where == NULL) {
  219                         needed += sizeof(buf);  /* be conservative */
  220                 } else {
  221                         slen = snprintf(buf, sizeof(buf), "%s%s(q=%d, f=%" PRId64
  222                                         " Hz)", spc, tc->tc_name, tc->tc_quality,
  223                                         tc->tc_frequency);
  224                         if (left < slen + 1)
  225                                 break;
  226                         mods = timecounter_mods;
  227                         mutex_spin_exit(&timecounter_lock);
  228                         error = copyout(buf, where, slen + 1);
  229                         mutex_spin_enter(&timecounter_lock);
  230                         if (mods != timecounter_mods) {
  231                                 goto retry;
  232                         }
  233                         spc = " ";
  234                         where += slen;
  235                         needed += slen;
  236                         left -= slen;
  237                 }
  238         }
  239         mutex_spin_exit(&timecounter_lock);
  240 
  241         *oldlenp = needed;
  242         return error;
  243 }
  244 
  245 SYSCTL_SETUP(sysctl_timecounter_setup, "sysctl timecounter setup")
  246 {
  247         const struct sysctlnode *node;
  248 
  249         sysctl_createv(clog, 0, NULL, &node,
  250                        CTLFLAG_PERMANENT,
  251                        CTLTYPE_NODE, "timecounter",
  252                        SYSCTL_DESCR("time counter information"),
  253                        NULL, 0, NULL, 0,
  254                        CTL_KERN, CTL_CREATE, CTL_EOL);
  255 
  256         if (node != NULL) {
  257                 sysctl_createv(clog, 0, NULL, NULL,
  258                                CTLFLAG_PERMANENT,
  259                                CTLTYPE_STRING, "choice",
  260                                SYSCTL_DESCR("available counters"),
  261                                sysctl_kern_timecounter_choice, 0, NULL, 0,
  262                                CTL_KERN, node->sysctl_num, CTL_CREATE, CTL_EOL);
  263 
  264                 sysctl_createv(clog, 0, NULL, NULL,
  265                                CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
  266                                CTLTYPE_STRING, "hardware",
  267                                SYSCTL_DESCR("currently active time counter"),
  268                                sysctl_kern_timecounter_hardware, 0, NULL, MAX_TCNAMELEN,
  269                                CTL_KERN, node->sysctl_num, CTL_CREATE, CTL_EOL);
  270 
  271                 sysctl_createv(clog, 0, NULL, NULL,
  272                                CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
  273                                CTLTYPE_INT, "timestepwarnings",
  274                                SYSCTL_DESCR("log time steps"),
  275                                NULL, 0, &timestepwarnings, 0,
  276                                CTL_KERN, node->sysctl_num, CTL_CREATE, CTL_EOL);
  277         }
  278 }
  279 
  280 #ifdef TC_COUNTERS
  281 #define TC_STATS(name)                                                  \
  282 static struct evcnt n##name =                                           \
  283     EVCNT_INITIALIZER(EVCNT_TYPE_MISC, NULL, "timecounter", #name);     \
  284 EVCNT_ATTACH_STATIC(n##name)
  285 TC_STATS(binuptime);    TC_STATS(nanouptime);    TC_STATS(microuptime);
  286 TC_STATS(bintime);      TC_STATS(nanotime);      TC_STATS(microtime);
  287 TC_STATS(getbinuptime); TC_STATS(getnanouptime); TC_STATS(getmicrouptime);
  288 TC_STATS(getbintime);   TC_STATS(getnanotime);   TC_STATS(getmicrotime);
  289 TC_STATS(setclock);
  290 #define TC_COUNT(var)   var.ev_count++
  291 #undef TC_STATS
  292 #else
  293 #define TC_COUNT(var)   /* nothing */
  294 #endif  /* TC_COUNTERS */
  295 
  296 static void tc_windup(void);
  297 
  298 /*
  299  * Return the difference between the timehands' counter value now and what
  300  * was when we copied it to the timehands' offset_count.
  301  */
  302 static inline u_int
  303 tc_delta(struct timehands *th)
  304 {
  305         struct timecounter *tc;
  306 
  307         tc = th->th_counter;
  308         return (tc->tc_get_timecount(tc) -
  309                  th->th_offset_count) & tc->tc_counter_mask;
  310 }
  311 
  312 /*
  313  * Functions for reading the time.  We have to loop until we are sure that
  314  * the timehands that we operated on was not updated under our feet.  See
  315  * the comment in <sys/timevar.h> for a description of these 12 functions.
  316  */
  317 
  318 void
  319 binuptime(struct bintime *bt)
  320 {
  321         struct timehands *th;
  322         lwp_t *l;
  323         u_int lgen, gen;
  324 
  325         TC_COUNT(nbinuptime);
  326 
  327         /*
  328          * Provide exclusion against tc_detach().
  329          *
  330          * We record the number of timecounter removals before accessing
  331          * timecounter state.  Note that the LWP can be using multiple
  332          * "generations" at once, due to interrupts (interrupted while in
  333          * this function).  Hardware interrupts will borrow the interrupted
  334          * LWP's l_tcgen value for this purpose, and can themselves be
  335          * interrupted by higher priority interrupts.  In this case we need
  336          * to ensure that the oldest generation in use is recorded.
  337          *
  338          * splsched() is too expensive to use, so we take care to structure
  339          * this code in such a way that it is not required.  Likewise, we
  340          * do not disable preemption.
  341          *
  342          * Memory barriers are also too expensive to use for such a
  343          * performance critical function.  The good news is that we do not
  344          * need memory barriers for this type of exclusion, as the thread
  345          * updating timecounter_removals will issue a broadcast cross call
  346          * before inspecting our l_tcgen value (this elides memory ordering
  347          * issues).
  348          */
  349         l = curlwp;
  350         lgen = l->l_tcgen;
  351         if (__predict_true(lgen == 0)) {
  352                 l->l_tcgen = timecounter_removals;
  353         }
  354         __insn_barrier();
  355 
  356         do {
  357                 th = timehands;
  358                 gen = th->th_generation;
  359                 *bt = th->th_offset;
  360                 bintime_addx(bt, th->th_scale * tc_delta(th));
  361         } while (gen == 0 || gen != th->th_generation);
  362 
  363         __insn_barrier();
  364         l->l_tcgen = lgen;
  365 }
  366 
  367 void
  368 nanouptime(struct timespec *tsp)
  369 {
  370         struct bintime bt;
  371 
  372         TC_COUNT(nnanouptime);
  373         binuptime(&bt);
  374         bintime2timespec(&bt, tsp);
  375 }
  376 
  377 void
  378 microuptime(struct timeval *tvp)
  379 {
  380         struct bintime bt;
  381 
  382         TC_COUNT(nmicrouptime);
  383         binuptime(&bt);
  384         bintime2timeval(&bt, tvp);
  385 }
  386 
  387 void
  388 bintime(struct bintime *bt)
  389 {
  390 
  391         TC_COUNT(nbintime);
  392         binuptime(bt);
  393         bintime_add(bt, &timebasebin);
  394 }
  395 
  396 void
  397 nanotime(struct timespec *tsp)
  398 {
  399         struct bintime bt;
  400 
  401         TC_COUNT(nnanotime);
  402         bintime(&bt);
  403         bintime2timespec(&bt, tsp);
  404 }
  405 
  406 void
  407 microtime(struct timeval *tvp)
  408 {
  409         struct bintime bt;
  410 
  411         TC_COUNT(nmicrotime);
  412         bintime(&bt);
  413         bintime2timeval(&bt, tvp);
  414 }
  415 
  416 void
  417 getbinuptime(struct bintime *bt)
  418 {
  419         struct timehands *th;
  420         u_int gen;
  421 
  422         TC_COUNT(ngetbinuptime);
  423         do {
  424                 th = timehands;
  425                 gen = th->th_generation;
  426                 *bt = th->th_offset;
  427         } while (gen == 0 || gen != th->th_generation);
  428 }
  429 
  430 void
  431 getnanouptime(struct timespec *tsp)
  432 {
  433         struct timehands *th;
  434         u_int gen;
  435 
  436         TC_COUNT(ngetnanouptime);
  437         do {
  438                 th = timehands;
  439                 gen = th->th_generation;
  440                 bintime2timespec(&th->th_offset, tsp);
  441         } while (gen == 0 || gen != th->th_generation);
  442 }
  443 
  444 void
  445 getmicrouptime(struct timeval *tvp)
  446 {
  447         struct timehands *th;
  448         u_int gen;
  449 
  450         TC_COUNT(ngetmicrouptime);
  451         do {
  452                 th = timehands;
  453                 gen = th->th_generation;
  454                 bintime2timeval(&th->th_offset, tvp);
  455         } while (gen == 0 || gen != th->th_generation);
  456 }
  457 
  458 void
  459 getbintime(struct bintime *bt)
  460 {
  461         struct timehands *th;
  462         u_int gen;
  463 
  464         TC_COUNT(ngetbintime);
  465         do {
  466                 th = timehands;
  467                 gen = th->th_generation;
  468                 *bt = th->th_offset;
  469         } while (gen == 0 || gen != th->th_generation);
  470         bintime_add(bt, &timebasebin);
  471 }
  472 
  473 static inline void
  474 dogetnanotime(struct timespec *tsp)
  475 {
  476         struct timehands *th;
  477         u_int gen;
  478 
  479         TC_COUNT(ngetnanotime);
  480         do {
  481                 th = timehands;
  482                 gen = th->th_generation;
  483                 *tsp = th->th_nanotime;
  484         } while (gen == 0 || gen != th->th_generation);
  485 }
  486 
  487 void
  488 getnanotime(struct timespec *tsp)
  489 {
  490 
  491         dogetnanotime(tsp);
  492 }
  493 
  494 void dtrace_getnanotime(struct timespec *tsp);
  495 
  496 void
  497 dtrace_getnanotime(struct timespec *tsp)
  498 {
  499 
  500         dogetnanotime(tsp);
  501 }
  502 
  503 void
  504 getmicrotime(struct timeval *tvp)
  505 {
  506         struct timehands *th;
  507         u_int gen;
  508 
  509         TC_COUNT(ngetmicrotime);
  510         do {
  511                 th = timehands;
  512                 gen = th->th_generation;
  513                 *tvp = th->th_microtime;
  514         } while (gen == 0 || gen != th->th_generation);
  515 }
  516 
  517 void
  518 getnanoboottime(struct timespec *tsp)
  519 {
  520         struct bintime bt;
  521 
  522         getbinboottime(&bt);
  523         bintime2timespec(&bt, tsp);
  524 }
  525 
  526 void
  527 getmicroboottime(struct timeval *tvp)
  528 {
  529         struct bintime bt;
  530 
  531         getbinboottime(&bt);
  532         bintime2timeval(&bt, tvp);
  533 }
  534 
  535 void
  536 getbinboottime(struct bintime *bt)
  537 {
  538 
  539         /*
  540          * XXX Need lockless read synchronization around timebasebin
  541          * (and not just here).
  542          */
  543         *bt = timebasebin;
  544 }
  545 
  546 /*
  547  * Initialize a new timecounter and possibly use it.
  548  */
  549 void
  550 tc_init(struct timecounter *tc)
  551 {
  552         u_int u;
  553 
  554         KASSERTMSG(tc->tc_next == NULL, "timecounter %s already initialised",
  555             tc->tc_name);
  556 
  557         u = tc->tc_frequency / tc->tc_counter_mask;
  558         /* XXX: We need some margin here, 10% is a guess */
  559         u *= 11;
  560         u /= 10;
  561         if (u > hz && tc->tc_quality >= 0) {
  562                 tc->tc_quality = -2000;
  563                 aprint_verbose(
  564                     "timecounter: Timecounter \"%s\" frequency %ju Hz",
  565                             tc->tc_name, (uintmax_t)tc->tc_frequency);
  566                 aprint_verbose(" -- Insufficient hz, needs at least %u\n", u);
  567         } else if (tc->tc_quality >= 0 || bootverbose) {
  568                 aprint_verbose(
  569                     "timecounter: Timecounter \"%s\" frequency %ju Hz "
  570                     "quality %d\n", tc->tc_name, (uintmax_t)tc->tc_frequency,
  571                     tc->tc_quality);
  572         }
  573 
  574         mutex_spin_enter(&timecounter_lock);
  575         tc->tc_next = timecounters;
  576         timecounters = tc;
  577         timecounter_mods++;
  578         /*
  579          * Never automatically use a timecounter with negative quality.
  580          * Even though we run on the dummy counter, switching here may be
  581          * worse since this timecounter may not be monotonous.
  582          */
  583         if (tc->tc_quality >= 0 && (tc->tc_quality > timecounter->tc_quality ||
  584             (tc->tc_quality == timecounter->tc_quality &&
  585             tc->tc_frequency > timecounter->tc_frequency))) {
  586                 (void)tc->tc_get_timecount(tc);
  587                 (void)tc->tc_get_timecount(tc);
  588                 timecounter = tc;
  589                 tc_windup();
  590         }
  591         mutex_spin_exit(&timecounter_lock);
  592 }
  593 
  594 /*
  595  * Pick a new timecounter due to the existing counter going bad.
  596  */
  597 static void
  598 tc_pick(void)
  599 {
  600         struct timecounter *best, *tc;
  601 
  602         KASSERT(mutex_owned(&timecounter_lock));
  603 
  604         for (best = tc = timecounters; tc != NULL; tc = tc->tc_next) {
  605                 if (tc->tc_quality > best->tc_quality)
  606                         best = tc;
  607                 else if (tc->tc_quality < best->tc_quality)
  608                         continue;
  609                 else if (tc->tc_frequency > best->tc_frequency)
  610                         best = tc;
  611         }
  612         (void)best->tc_get_timecount(best);
  613         (void)best->tc_get_timecount(best);
  614         timecounter = best;
  615 }
  616 
  617 /*
  618  * A timecounter has gone bad, arrange to pick a new one at the next
  619  * clock tick.
  620  */
  621 void
  622 tc_gonebad(struct timecounter *tc)
  623 {
  624 
  625         tc->tc_quality = -100;
  626         membar_producer();
  627         atomic_inc_uint(&timecounter_bad);
  628 }
  629 
  630 /*
  631  * Stop using a timecounter and remove it from the timecounters list.
  632  */
  633 int
  634 tc_detach(struct timecounter *target)
  635 {
  636         struct timecounter *tc;
  637         struct timecounter **tcp = NULL;
  638         int removals;
  639         lwp_t *l;
  640 
  641         /* First, find the timecounter. */
  642         mutex_spin_enter(&timecounter_lock);
  643         for (tcp = &timecounters, tc = timecounters;
  644              tc != NULL;
  645              tcp = &tc->tc_next, tc = tc->tc_next) {
  646                 if (tc == target)
  647                         break;
  648         }
  649         if (tc == NULL) {
  650                 mutex_spin_exit(&timecounter_lock);
  651                 return ESRCH;
  652         }
  653 
  654         /* And now, remove it. */
  655         *tcp = tc->tc_next;
  656         if (timecounter == target) {
  657                 tc_pick();
  658                 tc_windup();
  659         }
  660         timecounter_mods++;
  661         removals = timecounter_removals++;
  662         mutex_spin_exit(&timecounter_lock);
  663 
  664         /*
  665          * We now have to determine if any threads in the system are still
  666          * making use of this timecounter.
  667          *
  668          * We issue a broadcast cross call to elide memory ordering issues,
  669          * then scan all LWPs in the system looking at each's timecounter
  670          * generation number.  We need to see a value of zero (not actively
  671          * using a timecounter) or a value greater than our removal value.
  672          *
  673          * We may race with threads that read `timecounter_removals' and
  674          * and then get preempted before updating `l_tcgen'.  This is not
  675          * a problem, since it means that these threads have not yet started
  676          * accessing timecounter state.  All we do need is one clean
  677          * snapshot of the system where every thread appears not to be using
  678          * old timecounter state.
  679          */
  680         for (;;) {
  681                 xc_barrier(0);
  682 
  683                 mutex_enter(&proc_lock);
  684                 LIST_FOREACH(l, &alllwp, l_list) {
  685                         if (l->l_tcgen == 0 || l->l_tcgen > removals) {
  686                                 /*
  687                                  * Not using timecounter or old timecounter
  688                                  * state at time of our xcall or later.
  689                                  */
  690                                 continue;
  691                         }
  692                         break;
  693                 }
  694                 mutex_exit(&proc_lock);
  695 
  696                 /*
  697                  * If the timecounter is still in use, wait at least 10ms
  698                  * before retrying.
  699                  */
  700                 if (l == NULL) {
  701                         break;
  702                 }
  703                 (void)kpause("tcdetach", false, mstohz(10), NULL);
  704         }
  705 
  706         tc->tc_next = NULL;
  707         return 0;
  708 }
  709 
  710 /* Report the frequency of the current timecounter. */
  711 uint64_t
  712 tc_getfrequency(void)
  713 {
  714 
  715         return timehands->th_counter->tc_frequency;
  716 }
  717 
  718 /*
  719  * Step our concept of UTC.  This is done by modifying our estimate of
  720  * when we booted.
  721  */
  722 void
  723 tc_setclock(const struct timespec *ts)
  724 {
  725         struct timespec ts2;
  726         struct bintime bt, bt2;
  727 
  728         mutex_spin_enter(&timecounter_lock);
  729         TC_COUNT(nsetclock);
  730         binuptime(&bt2);
  731         timespec2bintime(ts, &bt);
  732         bintime_sub(&bt, &bt2);
  733         bintime_add(&bt2, &timebasebin);
  734         timebasebin = bt;
  735         tc_windup();
  736         mutex_spin_exit(&timecounter_lock);
  737 
  738         if (timestepwarnings) {
  739                 bintime2timespec(&bt2, &ts2);
  740                 log(LOG_INFO,
  741                     "Time stepped from %lld.%09ld to %lld.%09ld\n",
  742                     (long long)ts2.tv_sec, ts2.tv_nsec,
  743                     (long long)ts->tv_sec, ts->tv_nsec);
  744         }
  745 }
  746 
  747 /*
  748  * Initialize the next struct timehands in the ring and make
  749  * it the active timehands.  Along the way we might switch to a different
  750  * timecounter and/or do seconds processing in NTP.  Slightly magic.
  751  */
  752 static void
  753 tc_windup(void)
  754 {
  755         struct bintime bt;
  756         struct timehands *th, *tho;
  757         uint64_t scale;
  758         u_int delta, ncount, ogen;
  759         int i, s_update;
  760         time_t t;
  761 
  762         KASSERT(mutex_owned(&timecounter_lock));
  763 
  764         s_update = 0;
  765 
  766         /*
  767          * Make the next timehands a copy of the current one, but do not
  768          * overwrite the generation or next pointer.  While we update
  769          * the contents, the generation must be zero.  Ensure global
  770          * visibility of the generation before proceeding.
  771          */
  772         tho = timehands;
  773         th = tho->th_next;
  774         ogen = th->th_generation;
  775         th->th_generation = 0;
  776         membar_producer();
  777         bcopy(tho, th, offsetof(struct timehands, th_generation));
  778 
  779         /*
  780          * Capture a timecounter delta on the current timecounter and if
  781          * changing timecounters, a counter value from the new timecounter.
  782          * Update the offset fields accordingly.
  783          */
  784         delta = tc_delta(th);
  785         if (th->th_counter != timecounter)
  786                 ncount = timecounter->tc_get_timecount(timecounter);
  787         else
  788                 ncount = 0;
  789         th->th_offset_count += delta;
  790         bintime_addx(&th->th_offset, th->th_scale * delta);
  791 
  792         /*
  793          * Hardware latching timecounters may not generate interrupts on
  794          * PPS events, so instead we poll them.  There is a finite risk that
  795          * the hardware might capture a count which is later than the one we
  796          * got above, and therefore possibly in the next NTP second which might
  797          * have a different rate than the current NTP second.  It doesn't
  798          * matter in practice.
  799          */
  800         if (tho->th_counter->tc_poll_pps)
  801                 tho->th_counter->tc_poll_pps(tho->th_counter);
  802 
  803         /*
  804          * Deal with NTP second processing.  The for loop normally
  805          * iterates at most once, but in extreme situations it might
  806          * keep NTP sane if timeouts are not run for several seconds.
  807          * At boot, the time step can be large when the TOD hardware
  808          * has been read, so on really large steps, we call
  809          * ntp_update_second only twice.  We need to call it twice in
  810          * case we missed a leap second.
  811          * If NTP is not compiled in ntp_update_second still calculates
  812          * the adjustment resulting from adjtime() calls.
  813          */
  814         bt = th->th_offset;
  815         bintime_add(&bt, &timebasebin);
  816         i = bt.sec - tho->th_microtime.tv_sec;
  817         if (i > LARGE_STEP)
  818                 i = 2;
  819         for (; i > 0; i--) {
  820                 t = bt.sec;
  821                 ntp_update_second(&th->th_adjustment, &bt.sec);
  822                 s_update = 1;
  823                 if (bt.sec != t)
  824                         timebasebin.sec += bt.sec - t;
  825         }
  826 
  827         /* Update the UTC timestamps used by the get*() functions. */
  828         /* XXX shouldn't do this here.  Should force non-`get' versions. */
  829         bintime2timeval(&bt, &th->th_microtime);
  830         bintime2timespec(&bt, &th->th_nanotime);
  831         /* Now is a good time to change timecounters. */
  832         if (th->th_counter != timecounter) {
  833                 th->th_counter = timecounter;
  834                 th->th_offset_count = ncount;
  835                 s_update = 1;
  836         }
  837 
  838         /*-
  839          * Recalculate the scaling factor.  We want the number of 1/2^64
  840          * fractions of a second per period of the hardware counter, taking
  841          * into account the th_adjustment factor which the NTP PLL/adjtime(2)
  842          * processing provides us with.
  843          *
  844          * The th_adjustment is nanoseconds per second with 32 bit binary
  845          * fraction and we want 64 bit binary fraction of second:
  846          *
  847          *       x = a * 2^32 / 10^9 = a * 4.294967296
  848          *
  849          * The range of th_adjustment is +/- 5000PPM so inside a 64bit int
  850          * we can only multiply by about 850 without overflowing, but that
  851          * leaves suitably precise fractions for multiply before divide.
  852          *
  853          * Divide before multiply with a fraction of 2199/512 results in a
  854          * systematic undercompensation of 10PPM of th_adjustment.  On a
  855          * 5000PPM adjustment this is a 0.05PPM error.  This is acceptable.
  856          *
  857          * We happily sacrifice the lowest of the 64 bits of our result
  858          * to the goddess of code clarity.
  859          *
  860          */
  861         if (s_update) {
  862                 scale = (uint64_t)1 << 63;
  863                 scale += (th->th_adjustment / 1024) * 2199;
  864                 scale /= th->th_counter->tc_frequency;
  865                 th->th_scale = scale * 2;
  866         }
  867         /*
  868          * Now that the struct timehands is again consistent, set the new
  869          * generation number, making sure to not make it zero.  Ensure
  870          * changes are globally visible before changing.
  871          */
  872         if (++ogen == 0)
  873                 ogen = 1;
  874         membar_producer();
  875         th->th_generation = ogen;
  876 
  877         /*
  878          * Go live with the new struct timehands.  Ensure changes are
  879          * globally visible before changing.
  880          */
  881         time_second = th->th_microtime.tv_sec;
  882         time_uptime = th->th_offset.sec;
  883         membar_producer();
  884         timehands = th;
  885 
  886         /*
  887          * Force users of the old timehand to move on.  This is
  888          * necessary for MP systems; we need to ensure that the
  889          * consumers will move away from the old timehand before
  890          * we begin updating it again when we eventually wrap
  891          * around.
  892          */
  893         if (++tho->th_generation == 0)
  894                 tho->th_generation = 1;
  895 }
  896 
  897 /*
  898  * RFC 2783 PPS-API implementation.
  899  */
  900 
  901 int
  902 pps_ioctl(u_long cmd, void *data, struct pps_state *pps)
  903 {
  904         pps_params_t *app;
  905         pps_info_t *pipi;
  906 #ifdef PPS_SYNC
  907         int *epi;
  908 #endif
  909 
  910         KASSERT(mutex_owned(&timecounter_lock));
  911 
  912         KASSERT(pps != NULL);
  913 
  914         switch (cmd) {
  915         case PPS_IOC_CREATE:
  916                 return 0;
  917         case PPS_IOC_DESTROY:
  918                 return 0;
  919         case PPS_IOC_SETPARAMS:
  920                 app = (pps_params_t *)data;
  921                 if (app->mode & ~pps->ppscap)
  922                         return EINVAL;
  923                 pps->ppsparam = *app;
  924                 return 0;
  925         case PPS_IOC_GETPARAMS:
  926                 app = (pps_params_t *)data;
  927                 *app = pps->ppsparam;
  928                 app->api_version = PPS_API_VERS_1;
  929                 return 0;
  930         case PPS_IOC_GETCAP:
  931                 *(int*)data = pps->ppscap;
  932                 return 0;
  933         case PPS_IOC_FETCH:
  934                 pipi = (pps_info_t *)data;
  935                 pps->ppsinfo.current_mode = pps->ppsparam.mode;
  936                 *pipi = pps->ppsinfo;
  937                 return 0;
  938         case PPS_IOC_KCBIND:
  939 #ifdef PPS_SYNC
  940                 epi = (int *)data;
  941                 /* XXX Only root should be able to do this */
  942                 if (*epi & ~pps->ppscap)
  943                         return EINVAL;
  944                 pps->kcmode = *epi;
  945                 return 0;
  946 #else
  947                 return EOPNOTSUPP;
  948 #endif
  949         default:
  950                 return EPASSTHROUGH;
  951         }
  952 }
  953 
  954 void
  955 pps_init(struct pps_state *pps)
  956 {
  957 
  958         KASSERT(mutex_owned(&timecounter_lock));
  959 
  960         pps->ppscap |= PPS_TSFMT_TSPEC;
  961         if (pps->ppscap & PPS_CAPTUREASSERT)
  962                 pps->ppscap |= PPS_OFFSETASSERT;
  963         if (pps->ppscap & PPS_CAPTURECLEAR)
  964                 pps->ppscap |= PPS_OFFSETCLEAR;
  965 }
  966 
  967 /*
  968  * capture a timetamp in the pps structure
  969  */
  970 void
  971 pps_capture(struct pps_state *pps)
  972 {
  973         struct timehands *th;
  974 
  975         KASSERT(mutex_owned(&timecounter_lock));
  976         KASSERT(pps != NULL);
  977 
  978         th = timehands;
  979         pps->capgen = th->th_generation;
  980         pps->capth = th;
  981         pps->capcount = (uint64_t)tc_delta(th) + th->th_offset_count;
  982         if (pps->capgen != th->th_generation)
  983                 pps->capgen = 0;
  984 }
  985 
  986 #ifdef PPS_DEBUG
  987 int ppsdebug = 0;
  988 #endif
  989 
  990 /*
  991  * process a pps_capture()ed event
  992  */
  993 void
  994 pps_event(struct pps_state *pps, int event)
  995 {
  996         pps_ref_event(pps, event, NULL, PPS_REFEVNT_PPS|PPS_REFEVNT_CAPTURE);
  997 }
  998 
  999 /*
 1000  * extended pps api /  kernel pll/fll entry point
 1001  *
 1002  * feed reference time stamps to PPS engine
 1003  *
 1004  * will simulate a PPS event and feed
 1005  * the NTP PLL/FLL if requested.
 1006  *
 1007  * the ref time stamps should be roughly once
 1008  * a second but do not need to be exactly in phase
 1009  * with the UTC second but should be close to it.
 1010  * this relaxation of requirements allows callout
 1011  * driven timestamping mechanisms to feed to pps 
 1012  * capture/kernel pll logic.
 1013  *
 1014  * calling pattern is:
 1015  *  pps_capture() (for PPS_REFEVNT_{CAPTURE|CAPCUR})
 1016  *  read timestamp from reference source
 1017  *  pps_ref_event()
 1018  *
 1019  * supported refmodes:
 1020  *  PPS_REFEVNT_CAPTURE
 1021  *    use system timestamp of pps_capture()
 1022  *  PPS_REFEVNT_CURRENT
 1023  *    use system timestamp of this call
 1024  *  PPS_REFEVNT_CAPCUR
 1025  *    use average of read capture and current system time stamp
 1026  *  PPS_REFEVNT_PPS
 1027  *    assume timestamp on second mark - ref_ts is ignored
 1028  *
 1029  */
 1030 
 1031 void
 1032 pps_ref_event(struct pps_state *pps,
 1033               int event,
 1034               struct bintime *ref_ts,
 1035               int refmode
 1036         )
 1037 {
 1038         struct bintime bt;      /* current time */
 1039         struct bintime btd;     /* time difference */
 1040         struct bintime bt_ref;  /* reference time */
 1041         struct timespec ts, *tsp, *osp;
 1042         struct timehands *th;
 1043         uint64_t tcount, acount, dcount, *pcount;
 1044         int foff, gen;
 1045 #ifdef PPS_SYNC
 1046         int fhard;
 1047 #endif
 1048         pps_seq_t *pseq;
 1049 
 1050         KASSERT(mutex_owned(&timecounter_lock));
 1051 
 1052         KASSERT(pps != NULL);
 1053 
 1054         /* pick up current time stamp if needed */
 1055         if (refmode & (PPS_REFEVNT_CURRENT|PPS_REFEVNT_CAPCUR)) {
 1056                 /* pick up current time stamp */
 1057                 th = timehands;
 1058                 gen = th->th_generation;
 1059                 tcount = (uint64_t)tc_delta(th) + th->th_offset_count;
 1060                 if (gen != th->th_generation)
 1061                         gen = 0;
 1062 
 1063                 /* If the timecounter was wound up underneath us, bail out. */
 1064                 if (pps->capgen == 0 ||
 1065                     pps->capgen != pps->capth->th_generation ||
 1066                     gen == 0 ||
 1067                     gen != pps->capgen) {
 1068 #ifdef PPS_DEBUG
 1069                         if (ppsdebug & 0x1) {
 1070                                 log(LOG_DEBUG,
 1071                                     "pps_ref_event(pps=%p, event=%d, ...): DROP (wind-up)\n",
 1072                                     pps, event);
 1073                         }
 1074 #endif
 1075                         return;
 1076                 }
 1077         } else {
 1078                 tcount = 0;     /* keep GCC happy */
 1079         }
 1080 
 1081 #ifdef PPS_DEBUG
 1082         if (ppsdebug & 0x1) {
 1083                 struct timespec tmsp;
 1084         
 1085                 if (ref_ts == NULL) {
 1086                         tmsp.tv_sec = 0;
 1087                         tmsp.tv_nsec = 0;
 1088                 } else {
 1089                         bintime2timespec(ref_ts, &tmsp);
 1090                 }
 1091 
 1092                 log(LOG_DEBUG,
 1093                     "pps_ref_event(pps=%p, event=%d, ref_ts=%"PRIi64
 1094                     ".%09"PRIi32", refmode=0x%1x)\n",
 1095                     pps, event, tmsp.tv_sec, (int32_t)tmsp.tv_nsec, refmode);
 1096         }
 1097 #endif
 1098 
 1099         /* setup correct event references */
 1100         if (event == PPS_CAPTUREASSERT) {
 1101                 tsp = &pps->ppsinfo.assert_timestamp;
 1102                 osp = &pps->ppsparam.assert_offset;
 1103                 foff = pps->ppsparam.mode & PPS_OFFSETASSERT;
 1104 #ifdef PPS_SYNC
 1105                 fhard = pps->kcmode & PPS_CAPTUREASSERT;
 1106 #endif
 1107                 pcount = &pps->ppscount[0];
 1108                 pseq = &pps->ppsinfo.assert_sequence;
 1109         } else {
 1110                 tsp = &pps->ppsinfo.clear_timestamp;
 1111                 osp = &pps->ppsparam.clear_offset;
 1112                 foff = pps->ppsparam.mode & PPS_OFFSETCLEAR;
 1113 #ifdef PPS_SYNC
 1114                 fhard = pps->kcmode & PPS_CAPTURECLEAR;
 1115 #endif
 1116                 pcount = &pps->ppscount[1];
 1117                 pseq = &pps->ppsinfo.clear_sequence;
 1118         }
 1119 
 1120         /* determine system time stamp according to refmode */
 1121         dcount = 0;             /* keep GCC happy */
 1122         switch (refmode & PPS_REFEVNT_RMASK) {
 1123         case PPS_REFEVNT_CAPTURE:
 1124                 acount = pps->capcount; /* use capture timestamp */
 1125                 break;
 1126 
 1127         case PPS_REFEVNT_CURRENT:
 1128                 acount = tcount; /* use current timestamp */
 1129                 break;
 1130 
 1131         case PPS_REFEVNT_CAPCUR:
 1132                 /*
 1133                  * calculate counter value between pps_capture() and
 1134                  * pps_ref_event()
 1135                  */
 1136                 dcount = tcount - pps->capcount;
 1137                 acount = (dcount / 2) + pps->capcount;
 1138                 break;
 1139 
 1140         default:                /* ignore call error silently */
 1141                 return;
 1142         }
 1143 
 1144         /*
 1145          * If the timecounter changed, we cannot compare the count values, so
 1146          * we have to drop the rest of the PPS-stuff until the next event.
 1147          */
 1148         if (pps->ppstc != pps->capth->th_counter) {
 1149                 pps->ppstc = pps->capth->th_counter;
 1150                 pps->capcount = acount;
 1151                 *pcount = acount;
 1152                 pps->ppscount[2] = acount;
 1153 #ifdef PPS_DEBUG
 1154                 if (ppsdebug & 0x1) {
 1155                         log(LOG_DEBUG,
 1156                             "pps_ref_event(pps=%p, event=%d, ...): DROP (time-counter change)\n",
 1157                             pps, event);
 1158                 }
 1159 #endif
 1160                 return;
 1161         }
 1162 
 1163         pps->capcount = acount;
 1164 
 1165         /* Convert the count to a bintime. */
 1166         bt = pps->capth->th_offset;
 1167         bintime_addx(&bt, pps->capth->th_scale * (acount - pps->capth->th_offset_count));
 1168         bintime_add(&bt, &timebasebin);
 1169 
 1170         if ((refmode & PPS_REFEVNT_PPS) == 0) {
 1171                 /* determine difference to reference time stamp */
 1172                 bt_ref = *ref_ts;
 1173 
 1174                 btd = bt;
 1175                 bintime_sub(&btd, &bt_ref);
 1176 
 1177                 /* 
 1178                  * simulate a PPS timestamp by dropping the fraction
 1179                  * and applying the offset
 1180                  */
 1181                 if (bt.frac >= (uint64_t)1<<63) /* skip to nearest second */
 1182                         bt.sec++;
 1183                 bt.frac = 0;
 1184                 bintime_add(&bt, &btd);
 1185         } else {
 1186                 /*
 1187                  * create ref_ts from current time - 
 1188                  * we are supposed to be called on
 1189                  * the second mark
 1190                  */
 1191                 bt_ref = bt;
 1192                 if (bt_ref.frac >= (uint64_t)1<<63)     /* skip to nearest second */
 1193                         bt_ref.sec++;
 1194                 bt_ref.frac = 0;
 1195         }
 1196 
 1197         /* convert bintime to timestamp */
 1198         bintime2timespec(&bt, &ts);
 1199 
 1200         /* If the timecounter was wound up underneath us, bail out. */
 1201         if (pps->capgen != pps->capth->th_generation)
 1202                 return;
 1203 
 1204         /* store time stamp */
 1205         *pcount = pps->capcount;
 1206         (*pseq)++;
 1207         *tsp = ts;
 1208 
 1209         /* add offset correction */
 1210         if (foff) {
 1211                 timespecadd(tsp, osp, tsp);
 1212                 if (tsp->tv_nsec < 0) {
 1213                         tsp->tv_nsec += 1000000000;
 1214                         tsp->tv_sec -= 1;
 1215                 }
 1216         }
 1217 
 1218 #ifdef PPS_DEBUG
 1219         if (ppsdebug & 0x2) {
 1220                 struct timespec ts2;
 1221                 struct timespec ts3;
 1222 
 1223                 bintime2timespec(&bt_ref, &ts2);
 1224 
 1225                 bt.sec = 0;
 1226                 bt.frac = 0;
 1227 
 1228                 if (refmode & PPS_REFEVNT_CAPCUR) {
 1229                             bintime_addx(&bt, pps->capth->th_scale * dcount);
 1230                 }
 1231                 bintime2timespec(&bt, &ts3);
 1232 
 1233                 log(LOG_DEBUG, "ref_ts=%"PRIi64".%09"PRIi32
 1234                     ", ts=%"PRIi64".%09"PRIi32", read latency=%"PRIi64" ns\n",
 1235                     ts2.tv_sec, (int32_t)ts2.tv_nsec,
 1236                     tsp->tv_sec, (int32_t)tsp->tv_nsec,
 1237                     timespec2ns(&ts3));
 1238         }
 1239 #endif
 1240 
 1241 #ifdef PPS_SYNC
 1242         if (fhard) {
 1243                 uint64_t scale;
 1244                 uint64_t div;
 1245 
 1246                 /*
 1247                  * Feed the NTP PLL/FLL.
 1248                  * The FLL wants to know how many (hardware) nanoseconds
 1249                  * elapsed since the previous event (mod 1 second) thus
 1250                  * we are actually looking at the frequency difference scaled
 1251                  * in nsec.
 1252                  * As the counter time stamps are not truly at 1Hz
 1253                  * we need to scale the count by the elapsed
 1254                  * reference time.
 1255                  * valid sampling interval: [0.5..2[ sec
 1256                  */
 1257 
 1258                 /* calculate elapsed raw count */
 1259                 tcount = pps->capcount - pps->ppscount[2];
 1260                 pps->ppscount[2] = pps->capcount;
 1261                 tcount &= pps->capth->th_counter->tc_counter_mask;
 1262                 
 1263                 /* calculate elapsed ref time */
 1264                 btd = bt_ref;
 1265                 bintime_sub(&btd, &pps->ref_time);
 1266                 pps->ref_time = bt_ref;
 1267 
 1268                 /* check that we stay below 2 sec */
 1269                 if (btd.sec < 0 || btd.sec > 1)
 1270                         return;
 1271 
 1272                 /* we want at least 0.5 sec between samples */
 1273                 if (btd.sec == 0 && btd.frac < (uint64_t)1<<63)
 1274                         return;
 1275 
 1276                 /*
 1277                  * calculate cycles per period by multiplying
 1278                  * the frequency with the elapsed period
 1279                  * we pick a fraction of 30 bits
 1280                  * ~1ns resolution for elapsed time
 1281                  */ 
 1282                 div   = (uint64_t)btd.sec << 30;
 1283                 div  |= (btd.frac >> 34) & (((uint64_t)1 << 30) - 1);
 1284                 div  *= pps->capth->th_counter->tc_frequency;
 1285                 div >>= 30;
 1286 
 1287                 if (div == 0)   /* safeguard */
 1288                         return;
 1289 
 1290                 scale = (uint64_t)1 << 63;
 1291                 scale /= div;
 1292                 scale *= 2;
 1293 
 1294                 bt.sec = 0;
 1295                 bt.frac = 0;
 1296                 bintime_addx(&bt, scale * tcount);
 1297                 bintime2timespec(&bt, &ts);
 1298 
 1299 #ifdef PPS_DEBUG
 1300                 if (ppsdebug & 0x4) {
 1301                         struct timespec ts2;
 1302                         int64_t df;
 1303 
 1304                         bintime2timespec(&bt_ref, &ts2);
 1305                         df = timespec2ns(&ts);
 1306                         if (df > 500000000)
 1307                                 df -= 1000000000;
 1308                         log(LOG_DEBUG, "hardpps: ref_ts=%"PRIi64
 1309                             ".%09"PRIi32", ts=%"PRIi64".%09"PRIi32
 1310                             ", freqdiff=%"PRIi64" ns/s\n",
 1311                             ts2.tv_sec, (int32_t)ts2.tv_nsec,
 1312                             tsp->tv_sec, (int32_t)tsp->tv_nsec,
 1313                             df);
 1314                 }
 1315 #endif
 1316 
 1317                 hardpps(tsp, timespec2ns(&ts));
 1318         }
 1319 #endif
 1320 }
 1321 
 1322 /*
 1323  * Timecounters need to be updated every so often to prevent the hardware
 1324  * counter from overflowing.  Updating also recalculates the cached values
 1325  * used by the get*() family of functions, so their precision depends on
 1326  * the update frequency.
 1327  */
 1328 
 1329 static int tc_tick;
 1330 
 1331 void
 1332 tc_ticktock(void)
 1333 {
 1334         static int count;
 1335 
 1336         if (++count < tc_tick)
 1337                 return;
 1338         count = 0;
 1339         mutex_spin_enter(&timecounter_lock);
 1340         if (__predict_false(timecounter_bad != 0)) {
 1341                 /* An existing timecounter has gone bad, pick a new one. */
 1342                 (void)atomic_swap_uint(&timecounter_bad, 0);
 1343                 if (timecounter->tc_quality < 0) {
 1344                         tc_pick();
 1345                 }
 1346         }
 1347         tc_windup();
 1348         mutex_spin_exit(&timecounter_lock);
 1349 }
 1350 
 1351 void
 1352 inittimecounter(void)
 1353 {
 1354         u_int p;
 1355 
 1356         mutex_init(&timecounter_lock, MUTEX_DEFAULT, IPL_HIGH);
 1357 
 1358         /*
 1359          * Set the initial timeout to
 1360          * max(1, <approx. number of hardclock ticks in a millisecond>).
 1361          * People should probably not use the sysctl to set the timeout
 1362          * to smaller than its initial value, since that value is the
 1363          * smallest reasonable one.  If they want better timestamps they
 1364          * should use the non-"get"* functions.
 1365          */
 1366         if (hz > 1000)
 1367                 tc_tick = (hz + 500) / 1000;
 1368         else
 1369                 tc_tick = 1;
 1370         p = (tc_tick * 1000000) / hz;
 1371         aprint_verbose("timecounter: Timecounters tick every %d.%03u msec\n",
 1372             p / 1000, p % 1000);
 1373 
 1374         /* warm up new timecounter (again) and get rolling. */
 1375         (void)timecounter->tc_get_timecount(timecounter);
 1376         (void)timecounter->tc_get_timecount(timecounter);
 1377 }
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FreeBSD/Linux Kernel Cross Reference sys/kern/kern_tc.c

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