kern_tc.c

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    1 /*-
    2  * ----------------------------------------------------------------------------
    3  * "THE BEER-WARE LICENSE" (Revision 42):
    4  * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
    5  * can do whatever you want with this stuff. If we meet some day, and you think
    6  * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
    7  * ----------------------------------------------------------------------------
    8  *
    9  * $FreeBSD: releng/5.0/sys/kern/kern_tc.c 108837 2003-01-06 22:47:16Z peter $
   10  */
   11 
   12 #include "opt_ntp.h"
   13 
   14 #include <sys/param.h>
   15 #include <sys/kernel.h>
   16 #include <sys/sysctl.h>
   17 #include <sys/systm.h>
   18 #include <sys/timepps.h>
   19 #include <sys/timetc.h>
   20 #include <sys/timex.h>
   21 
   22 /*
   23  * Implement a dummy timecounter which we can use until we get a real one
   24  * in the air.  This allows the console and other early stuff to use
   25  * time services.
   26  */
   27 
   28 static u_int
   29 dummy_get_timecount(struct timecounter *tc)
   30 {
   31         static u_int now;
   32 
   33         return (++now);
   34 }
   35 
   36 static struct timecounter dummy_timecounter = {
   37         dummy_get_timecount, 0, ~0u, 1000000, "dummy",
   38 };
   39 
   40 struct timehands {
   41         /* These fields must be initialized by the driver. */
   42         struct timecounter      *th_counter;
   43         int64_t                 th_adjustment;
   44         u_int64_t               th_scale;
   45         u_int                   th_offset_count;
   46         struct bintime          th_offset;
   47         struct timeval          th_microtime;
   48         struct timespec         th_nanotime;
   49         /* Fields not to be copied in tc_windup start with th_generation. */
   50         volatile u_int          th_generation;
   51         struct timehands        *th_next;
   52 };
   53 
   54 extern struct timehands th0;
   55 static struct timehands th9 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th0};
   56 static struct timehands th8 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th9};
   57 static struct timehands th7 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th8};
   58 static struct timehands th6 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th7};
   59 static struct timehands th5 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th6};
   60 static struct timehands th4 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th5};
   61 static struct timehands th3 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th4};
   62 static struct timehands th2 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th3};
   63 static struct timehands th1 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th2};
   64 static struct timehands th0 = {
   65         &dummy_timecounter,
   66         0,
   67         (uint64_t)-1 / 1000000,
   68         0,
   69         {1, 0},
   70         {0, 0},
   71         {0, 0},
   72         1,
   73         &th1
   74 };
   75 
   76 static struct timehands *volatile timehands = &th0;
   77 struct timecounter *timecounter = &dummy_timecounter;
   78 static struct timecounter *timecounters = &dummy_timecounter;
   79 
   80 time_t time_second = 1;
   81 time_t time_uptime = 0;
   82 
   83 static struct bintime boottimebin;
   84 struct timeval boottime;
   85 SYSCTL_STRUCT(_kern, KERN_BOOTTIME, boottime, CTLFLAG_RD,
   86     &boottime, timeval, "System boottime");
   87 
   88 SYSCTL_NODE(_kern, OID_AUTO, timecounter, CTLFLAG_RW, 0, "");
   89 
   90 #define TC_STATS(foo) \
   91         static u_int foo; \
   92         SYSCTL_UINT(_kern_timecounter, OID_AUTO, foo, CTLFLAG_RD, &foo, 0, "");\
   93         struct __hack
   94 
   95 TC_STATS(nbinuptime);    TC_STATS(nnanouptime);    TC_STATS(nmicrouptime);
   96 TC_STATS(nbintime);      TC_STATS(nnanotime);      TC_STATS(nmicrotime);
   97 TC_STATS(ngetbinuptime); TC_STATS(ngetnanouptime); TC_STATS(ngetmicrouptime);
   98 TC_STATS(ngetbintime);   TC_STATS(ngetnanotime);   TC_STATS(ngetmicrotime);
   99 
  100 #undef TC_STATS
  101 
  102 static void tc_windup(void);
  103 
  104 /*
  105  * Return the difference between the timehands' counter value now and what
  106  * was when we copied it to the timehands' offset_count.
  107  */
  108 static __inline u_int
  109 tc_delta(struct timehands *th)
  110 {
  111         struct timecounter *tc;
  112 
  113         tc = th->th_counter;
  114         return ((tc->tc_get_timecount(tc) - th->th_offset_count) &
  115             tc->tc_counter_mask);
  116 }
  117 
  118 /*
  119  * Functions for reading the time.  We have to loop until we are sure that
  120  * the timehands that we operated on was not updated under our feet.  See
  121  * the comment in <sys/time.h> for a description of these 12 functions.
  122  */
  123 
  124 void
  125 binuptime(struct bintime *bt)
  126 {
  127         struct timehands *th;
  128         u_int gen;
  129 
  130         nbinuptime++;
  131         do {
  132                 th = timehands;
  133                 gen = th->th_generation;
  134                 *bt = th->th_offset;
  135                 bintime_addx(bt, th->th_scale * tc_delta(th));
  136         } while (gen == 0 || gen != th->th_generation);
  137 }
  138 
  139 void
  140 nanouptime(struct timespec *tsp)
  141 {
  142         struct bintime bt;
  143 
  144         nnanouptime++;
  145         binuptime(&bt);
  146         bintime2timespec(&bt, tsp);
  147 }
  148 
  149 void
  150 microuptime(struct timeval *tvp)
  151 {
  152         struct bintime bt;
  153 
  154         nmicrouptime++;
  155         binuptime(&bt);
  156         bintime2timeval(&bt, tvp);
  157 }
  158 
  159 void
  160 bintime(struct bintime *bt)
  161 {
  162 
  163         nbintime++;
  164         binuptime(bt);
  165         bintime_add(bt, &boottimebin);
  166 }
  167 
  168 void
  169 nanotime(struct timespec *tsp)
  170 {
  171         struct bintime bt;
  172 
  173         nnanotime++;
  174         bintime(&bt);
  175         bintime2timespec(&bt, tsp);
  176 }
  177 
  178 void
  179 microtime(struct timeval *tvp)
  180 {
  181         struct bintime bt;
  182 
  183         nmicrotime++;
  184         bintime(&bt);
  185         bintime2timeval(&bt, tvp);
  186 }
  187 
  188 void
  189 getbinuptime(struct bintime *bt)
  190 {
  191         struct timehands *th;
  192         u_int gen;
  193 
  194         ngetbinuptime++;
  195         do {
  196                 th = timehands;
  197                 gen = th->th_generation;
  198                 *bt = th->th_offset;
  199         } while (gen == 0 || gen != th->th_generation);
  200 }
  201 
  202 void
  203 getnanouptime(struct timespec *tsp)
  204 {
  205         struct timehands *th;
  206         u_int gen;
  207 
  208         ngetnanouptime++;
  209         do {
  210                 th = timehands;
  211                 gen = th->th_generation;
  212                 bintime2timespec(&th->th_offset, tsp);
  213         } while (gen == 0 || gen != th->th_generation);
  214 }
  215 
  216 void
  217 getmicrouptime(struct timeval *tvp)
  218 {
  219         struct timehands *th;
  220         u_int gen;
  221 
  222         ngetmicrouptime++;
  223         do {
  224                 th = timehands;
  225                 gen = th->th_generation;
  226                 bintime2timeval(&th->th_offset, tvp);
  227         } while (gen == 0 || gen != th->th_generation);
  228 }
  229 
  230 void
  231 getbintime(struct bintime *bt)
  232 {
  233         struct timehands *th;
  234         u_int gen;
  235 
  236         ngetbintime++;
  237         do {
  238                 th = timehands;
  239                 gen = th->th_generation;
  240                 *bt = th->th_offset;
  241         } while (gen == 0 || gen != th->th_generation);
  242         bintime_add(bt, &boottimebin);
  243 }
  244 
  245 void
  246 getnanotime(struct timespec *tsp)
  247 {
  248         struct timehands *th;
  249         u_int gen;
  250 
  251         ngetnanotime++;
  252         do {
  253                 th = timehands;
  254                 gen = th->th_generation;
  255                 *tsp = th->th_nanotime;
  256         } while (gen == 0 || gen != th->th_generation);
  257 }
  258 
  259 void
  260 getmicrotime(struct timeval *tvp)
  261 {
  262         struct timehands *th;
  263         u_int gen;
  264 
  265         ngetmicrotime++;
  266         do {
  267                 th = timehands;
  268                 gen = th->th_generation;
  269                 *tvp = th->th_microtime;
  270         } while (gen == 0 || gen != th->th_generation);
  271 }
  272 
  273 /*
  274  * Initialize a new timecounter.
  275  * We should really try to rank the timecounters and intelligently determine
  276  * if the new timecounter is better than the current one.  This is subject
  277  * to further study.  For now always use the new timecounter.
  278  */
  279 void
  280 tc_init(struct timecounter *tc)
  281 {
  282         unsigned u;
  283 
  284         printf("Timecounter \"%s\"  frequency %lu Hz",
  285             tc->tc_name, (u_long)tc->tc_frequency);
  286 
  287         u = tc->tc_frequency / tc->tc_counter_mask;
  288         if (u > hz) {
  289                 printf(" -- Insufficient hz, needs at least %u\n", u);
  290                 return;
  291         }
  292         tc->tc_next = timecounters;
  293         timecounters = tc;
  294         printf("\n");
  295         (void)tc->tc_get_timecount(tc);
  296         (void)tc->tc_get_timecount(tc);
  297         timecounter = tc;
  298 }
  299 
  300 /* Report the frequency of the current timecounter. */
  301 u_int32_t
  302 tc_getfrequency(void)
  303 {
  304 
  305         return (timehands->th_counter->tc_frequency);
  306 }
  307 
  308 /*
  309  * Step our concept of GMT.  This is done by modifying our estimate of
  310  * when we booted.  XXX: needs futher work.
  311  */
  312 void
  313 tc_setclock(struct timespec *ts)
  314 {
  315         struct timespec ts2;
  316 
  317         nanouptime(&ts2);
  318         boottime.tv_sec = ts->tv_sec - ts2.tv_sec;
  319         /* XXX boottime should probably be a timespec. */
  320         boottime.tv_usec = (ts->tv_nsec - ts2.tv_nsec) / 1000;
  321         if (boottime.tv_usec < 0) {
  322                 boottime.tv_usec += 1000000;
  323                 boottime.tv_sec--;
  324         }
  325         timeval2bintime(&boottime, &boottimebin);
  326 
  327         /* XXX fiddle all the little crinkly bits around the fiords... */
  328         tc_windup();
  329 }
  330 
  331 /*
  332  * Initialize the next struct timehands in the ring and make
  333  * it the active timehands.  Along the way we might switch to a different
  334  * timecounter and/or do seconds processing in NTP.  Slightly magic.
  335  */
  336 static void
  337 tc_windup(void)
  338 {
  339         struct bintime bt;
  340         struct timehands *th, *tho;
  341         u_int64_t scale;
  342         u_int delta, ncount, ogen;
  343         int i;
  344 
  345         /*
  346          * Make the next timehands a copy of the current one, but do not
  347          * overwrite the generation or next pointer.  While we update
  348          * the contents, the generation must be zero.
  349          */
  350         tho = timehands;
  351         th = tho->th_next;
  352         ogen = th->th_generation;
  353         th->th_generation = 0;
  354         bcopy(tho, th, offsetof(struct timehands, th_generation));
  355 
  356         /*
  357          * Capture a timecounter delta on the current timecounter and if
  358          * changing timecounters, a counter value from the new timecounter.
  359          * Update the offset fields accordingly.
  360          */
  361         delta = tc_delta(th);
  362         if (th->th_counter != timecounter)
  363                 ncount = timecounter->tc_get_timecount(timecounter);
  364         else
  365                 ncount = 0;
  366         th->th_offset_count += delta;
  367         th->th_offset_count &= th->th_counter->tc_counter_mask;
  368         bintime_addx(&th->th_offset, th->th_scale * delta);
  369 
  370         /*
  371          * Hardware latching timecounters may not generate interrupts on
  372          * PPS events, so instead we poll them.  There is a finite risk that
  373          * the hardware might capture a count which is later than the one we
  374          * got above, and therefore possibly in the next NTP second which might
  375          * have a different rate than the current NTP second.  It doesn't
  376          * matter in practice.
  377          */
  378         if (tho->th_counter->tc_poll_pps)
  379                 tho->th_counter->tc_poll_pps(tho->th_counter);
  380 
  381         /*
  382          * Deal with NTP second processing.  The for loop normally only
  383          * iterates once, but in extreme situations it might keep NTP sane
  384          * if timeouts are not run for several seconds.
  385          */
  386         for (i = th->th_offset.sec - tho->th_offset.sec; i > 0; i--)
  387                 ntp_update_second(&th->th_adjustment, &th->th_offset.sec);
  388 
  389         /* Now is a good time to change timecounters. */
  390         if (th->th_counter != timecounter) {
  391                 th->th_counter = timecounter;
  392                 th->th_offset_count = ncount;
  393         }
  394 
  395         /*-
  396          * Recalculate the scaling factor.  We want the number of 1/2^64
  397          * fractions of a second per period of the hardware counter, taking
  398          * into account the th_adjustment factor which the NTP PLL/adjtime(2)
  399          * processing provides us with.
  400          *
  401          * The th_adjustment is nanoseconds per second with 32 bit binary
  402          * fraction and want 64 bit binary fraction of second:
  403          *
  404          *       x = a * 2^32 / 10^9 = a * 4.294967296
  405          *
  406          * The range of th_adjustment is +/- 5000PPM so inside a 64bit int
  407          * we can only multiply by about 850 without overflowing, but that
  408          * leaves suitably precise fractions for multiply before divide.
  409          *
  410          * Divide before multiply with a fraction of 2199/512 results in a
  411          * systematic undercompensation of 10PPM of th_adjustment.  On a
  412          * 5000PPM adjustment this is a 0.05PPM error.  This is acceptable.
  413          *
  414          * We happily sacrifice the lowest of the 64 bits of our result
  415          * to the goddess of code clarity.
  416          *
  417          */
  418         scale = (u_int64_t)1 << 63;
  419         scale += (th->th_adjustment / 1024) * 2199;
  420         scale /= th->th_counter->tc_frequency;
  421         th->th_scale = scale * 2;
  422 
  423         /* Update the GMT timestamps used for the get*() functions. */
  424         bt = th->th_offset;
  425         bintime_add(&bt, &boottimebin);
  426         bintime2timeval(&bt, &th->th_microtime);
  427         bintime2timespec(&bt, &th->th_nanotime);
  428 
  429         /*
  430          * Now that the struct timehands is again consistent, set the new
  431          * generation number, making sure to not make it zero.
  432          */
  433         if (++ogen == 0)
  434                 ogen = 1;
  435         th->th_generation = ogen;
  436 
  437         /* Go live with the new struct timehands. */
  438         time_second = th->th_microtime.tv_sec;
  439         time_uptime = th->th_offset.sec;
  440         timehands = th;
  441 }
  442 
  443 /* Report or change the active timecounter hardware. */
  444 static int
  445 sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS)
  446 {
  447         char newname[32];
  448         struct timecounter *newtc, *tc;
  449         int error;
  450 
  451         tc = timecounter;
  452         strlcpy(newname, tc->tc_name, sizeof(newname));
  453 
  454         error = sysctl_handle_string(oidp, &newname[0], sizeof(newname), req);
  455         if (error != 0 || req->newptr == NULL ||
  456             strcmp(newname, tc->tc_name) == 0)
  457                 return (error);
  458         for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) {
  459                 if (strcmp(newname, newtc->tc_name) != 0)
  460                         continue;
  461 
  462                 /* Warm up new timecounter. */
  463                 (void)newtc->tc_get_timecount(newtc);
  464                 (void)newtc->tc_get_timecount(newtc);
  465 
  466                 timecounter = newtc;
  467                 return (0);
  468         }
  469         return (EINVAL);
  470 }
  471 
  472 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | CTLFLAG_RW,
  473     0, 0, sysctl_kern_timecounter_hardware, "A", "");
  474 
  475 /*
  476  * RFC 2783 PPS-API implementation.
  477  */
  478 
  479 int
  480 pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps)
  481 {
  482         pps_params_t *app;
  483         struct pps_fetch_args *fapi;
  484 #ifdef PPS_SYNC
  485         struct pps_kcbind_args *kapi;
  486 #endif
  487 
  488         switch (cmd) {
  489         case PPS_IOC_CREATE:
  490                 return (0);
  491         case PPS_IOC_DESTROY:
  492                 return (0);
  493         case PPS_IOC_SETPARAMS:
  494                 app = (pps_params_t *)data;
  495                 if (app->mode & ~pps->ppscap)
  496                         return (EINVAL);
  497                 pps->ppsparam = *app;
  498                 return (0);
  499         case PPS_IOC_GETPARAMS:
  500                 app = (pps_params_t *)data;
  501                 *app = pps->ppsparam;
  502                 app->api_version = PPS_API_VERS_1;
  503                 return (0);
  504         case PPS_IOC_GETCAP:
  505                 *(int*)data = pps->ppscap;
  506                 return (0);
  507         case PPS_IOC_FETCH:
  508                 fapi = (struct pps_fetch_args *)data;
  509                 if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC)
  510                         return (EINVAL);
  511                 if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec)
  512                         return (EOPNOTSUPP);
  513                 pps->ppsinfo.current_mode = pps->ppsparam.mode;
  514                 fapi->pps_info_buf = pps->ppsinfo;
  515                 return (0);
  516         case PPS_IOC_KCBIND:
  517 #ifdef PPS_SYNC
  518                 kapi = (struct pps_kcbind_args *)data;
  519                 /* XXX Only root should be able to do this */
  520                 if (kapi->tsformat && kapi->tsformat != PPS_TSFMT_TSPEC)
  521                         return (EINVAL);
  522                 if (kapi->kernel_consumer != PPS_KC_HARDPPS)
  523                         return (EINVAL);
  524                 if (kapi->edge & ~pps->ppscap)
  525                         return (EINVAL);
  526                 pps->kcmode = kapi->edge;
  527                 return (0);
  528 #else
  529                 return (EOPNOTSUPP);
  530 #endif
  531         default:
  532                 return (ENOTTY);
  533         }
  534 }
  535 
  536 void
  537 pps_init(struct pps_state *pps)
  538 {
  539         pps->ppscap |= PPS_TSFMT_TSPEC;
  540         if (pps->ppscap & PPS_CAPTUREASSERT)
  541                 pps->ppscap |= PPS_OFFSETASSERT;
  542         if (pps->ppscap & PPS_CAPTURECLEAR)
  543                 pps->ppscap |= PPS_OFFSETCLEAR;
  544 }
  545 
  546 void
  547 pps_capture(struct pps_state *pps)
  548 {
  549         struct timehands *th;
  550 
  551         th = timehands;
  552         pps->capgen = th->th_generation;
  553         pps->capth = th;
  554         pps->capcount = th->th_counter->tc_get_timecount(th->th_counter);
  555         if (pps->capgen != th->th_generation)
  556                 pps->capgen = 0;
  557 }
  558 
  559 void
  560 pps_event(struct pps_state *pps, int event)
  561 {
  562         struct bintime bt;
  563         struct timespec ts, *tsp, *osp;
  564         u_int tcount, *pcount;
  565         int foff, fhard;
  566         pps_seq_t *pseq;
  567 
  568         /* If the timecounter was wound up underneath us, bail out. */
  569         if (pps->capgen == 0 || pps->capgen != pps->capth->th_generation)
  570                 return;
  571 
  572         /* Things would be easier with arrays. */
  573         if (event == PPS_CAPTUREASSERT) {
  574                 tsp = &pps->ppsinfo.assert_timestamp;
  575                 osp = &pps->ppsparam.assert_offset;
  576                 foff = pps->ppsparam.mode & PPS_OFFSETASSERT;
  577                 fhard = pps->kcmode & PPS_CAPTUREASSERT;
  578                 pcount = &pps->ppscount[0];
  579                 pseq = &pps->ppsinfo.assert_sequence;
  580         } else {
  581                 tsp = &pps->ppsinfo.clear_timestamp;
  582                 osp = &pps->ppsparam.clear_offset;
  583                 foff = pps->ppsparam.mode & PPS_OFFSETCLEAR;
  584                 fhard = pps->kcmode & PPS_CAPTURECLEAR;
  585                 pcount = &pps->ppscount[1];
  586                 pseq = &pps->ppsinfo.clear_sequence;
  587         }
  588 
  589         /*
  590          * If the timecounter changed, we cannot compare the count values, so
  591          * we have to drop the rest of the PPS-stuff until the next event.
  592          */
  593         if (pps->ppstc != pps->capth->th_counter) {
  594                 pps->ppstc = pps->capth->th_counter;
  595                 *pcount = pps->capcount;
  596                 pps->ppscount[2] = pps->capcount;
  597                 return;
  598         }
  599 
  600         /* Return if nothing really happened. */
  601         if (*pcount == pps->capcount)
  602                 return;
  603 
  604         /* Convert the count to a timespec. */
  605         tcount = pps->capcount - pps->capth->th_offset_count;
  606         tcount &= pps->capth->th_counter->tc_counter_mask;
  607         bt = pps->capth->th_offset;
  608         bintime_addx(&bt, pps->capth->th_scale * tcount);
  609         bintime_add(&bt, &boottimebin);
  610         bintime2timespec(&bt, &ts);
  611 
  612         /* If the timecounter was wound up underneath us, bail out. */
  613         if (pps->capgen != pps->capth->th_generation)
  614                 return;
  615 
  616         *pcount = pps->capcount;
  617         (*pseq)++;
  618         *tsp = ts;
  619 
  620         if (foff) {
  621                 timespecadd(tsp, osp);
  622                 if (tsp->tv_nsec < 0) {
  623                         tsp->tv_nsec += 1000000000;
  624                         tsp->tv_sec -= 1;
  625                 }
  626         }
  627 #ifdef PPS_SYNC
  628         if (fhard) {
  629                 /*
  630                  * Feed the NTP PLL/FLL.
  631                  * The FLL wants to know how many nanoseconds elapsed since
  632                  * the previous event.
  633                  * I have never been able to convince myself that this code
  634                  * is actually correct:  Using th_scale is bound to contain
  635                  * a phase correction component from userland, when running
  636                  * as FLL, so the number hardpps() gets is not meaningful IMO.
  637                  */
  638                 tcount = pps->capcount - pps->ppscount[2];
  639                 pps->ppscount[2] = pps->capcount;
  640                 tcount &= pps->capth->th_counter->tc_counter_mask;
  641                 bt.sec = 0;
  642                 bt.frac = 0;
  643                 bintime_addx(&bt, pps->capth->th_scale * tcount);
  644                 bintime2timespec(&bt, &ts);
  645                 hardpps(tsp, ts.tv_nsec + 1000000000 * ts.tv_sec);
  646         }
  647 #endif
  648 }
  649 
  650 /*
  651  * Timecounters need to be updated every so often to prevent the hardware
  652  * counter from overflowing.  Updating also recalculates the cached values
  653  * used by the get*() family of functions, so their precision depends on
  654  * the update frequency.
  655  */
  656 
  657 static int tc_tick;
  658 SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tick, 0, "");
  659 
  660 void
  661 tc_ticktock(void)
  662 {
  663         static int count;
  664 
  665         if (++count < tc_tick)
  666                 return;
  667         count = 0;
  668         tc_windup();
  669 }
  670 
  671 static void
  672 inittimecounter(void *dummy)
  673 {
  674         u_int p;
  675 
  676         /*
  677          * Set the initial timeout to
  678          * max(1, <approx. number of hardclock ticks in a millisecond>).
  679          * People should probably not use the sysctl to set the timeout
  680          * to smaller than its inital value, since that value is the
  681          * smallest reasonable one.  If they want better timestamps they
  682          * should use the non-"get"* functions.
  683          */
  684         if (hz > 1000)
  685                 tc_tick = (hz + 500) / 1000;
  686         else
  687                 tc_tick = 1;
  688         p = (tc_tick * 1000000) / hz;
  689         printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000);
  690 
  691         /* warm up new timecounter (again) and get rolling. */
  692         (void)timecounter->tc_get_timecount(timecounter);
  693         (void)timecounter->tc_get_timecount(timecounter);
  694 }
  695 
  696 SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_SECOND, inittimecounter, NULL)
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FreeBSD/Linux Kernel Cross Reference sys/kern/kern_tc.c

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