Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_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 10 #include <sys/cdefs.h> 11 __FBSDID("$FreeBSD: releng/5.2/sys/kern/kern_tc.c 122610 2003-11-13 10:03:58Z phk $"); 12 13 #include "opt_ntp.h" 14 15 #include <sys/param.h> 16 #include <sys/kernel.h> 17 #include <sys/sysctl.h> 18 #include <sys/systm.h> 19 #include <sys/timepps.h> 20 #include <sys/timetc.h> 21 #include <sys/timex.h> 22 23 /* 24 * A large step happens on boot. This constant detects such steps. 25 * It is relatively small so that ntp_update_second gets called enough 26 * in the typical 'missed a couple of seconds' case, but doesn't loop 27 * forever when the time step is large. 28 */ 29 #define LARGE_STEP 200 30 31 /* 32 * Implement a dummy timecounter which we can use until we get a real one 33 * in the air. This allows the console and other early stuff to use 34 * time services. 35 */ 36 37 static u_int 38 dummy_get_timecount(struct timecounter *tc) 39 { 40 static u_int now; 41 42 return (++now); 43 } 44 45 static struct timecounter dummy_timecounter = { 46 dummy_get_timecount, 0, ~0u, 1000000, "dummy", -1000000 47 }; 48 49 struct timehands { 50 /* These fields must be initialized by the driver. */ 51 struct timecounter *th_counter; 52 int64_t th_adjustment; 53 u_int64_t th_scale; 54 u_int th_offset_count; 55 struct bintime th_offset; 56 struct timeval th_microtime; 57 struct timespec th_nanotime; 58 /* Fields not to be copied in tc_windup start with th_generation. */ 59 volatile u_int th_generation; 60 struct timehands *th_next; 61 }; 62 63 extern struct timehands th0; 64 static struct timehands th9 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th0}; 65 static struct timehands th8 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th9}; 66 static struct timehands th7 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th8}; 67 static struct timehands th6 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th7}; 68 static struct timehands th5 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th6}; 69 static struct timehands th4 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th5}; 70 static struct timehands th3 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th4}; 71 static struct timehands th2 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th3}; 72 static struct timehands th1 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th2}; 73 static struct timehands th0 = { 74 &dummy_timecounter, 75 0, 76 (uint64_t)-1 / 1000000, 77 0, 78 {1, 0}, 79 {0, 0}, 80 {0, 0}, 81 1, 82 &th1 83 }; 84 85 static struct timehands *volatile timehands = &th0; 86 struct timecounter *timecounter = &dummy_timecounter; 87 static struct timecounter *timecounters = &dummy_timecounter; 88 89 time_t time_second = 1; 90 time_t time_uptime = 0; 91 92 static struct bintime boottimebin; 93 struct timeval boottime; 94 SYSCTL_STRUCT(_kern, KERN_BOOTTIME, boottime, CTLFLAG_RD, 95 &boottime, timeval, "System boottime"); 96 97 SYSCTL_NODE(_kern, OID_AUTO, timecounter, CTLFLAG_RW, 0, ""); 98 99 #define TC_STATS(foo) \ 100 static u_int foo; \ 101 SYSCTL_UINT(_kern_timecounter, OID_AUTO, foo, CTLFLAG_RD, &foo, 0, "");\ 102 struct __hack 103 104 TC_STATS(nbinuptime); TC_STATS(nnanouptime); TC_STATS(nmicrouptime); 105 TC_STATS(nbintime); TC_STATS(nnanotime); TC_STATS(nmicrotime); 106 TC_STATS(ngetbinuptime); TC_STATS(ngetnanouptime); TC_STATS(ngetmicrouptime); 107 TC_STATS(ngetbintime); TC_STATS(ngetnanotime); TC_STATS(ngetmicrotime); 108 TC_STATS(nsetclock); 109 110 #undef TC_STATS 111 112 static void tc_windup(void); 113 114 /* 115 * Return the difference between the timehands' counter value now and what 116 * was when we copied it to the timehands' offset_count. 117 */ 118 static __inline u_int 119 tc_delta(struct timehands *th) 120 { 121 struct timecounter *tc; 122 123 tc = th->th_counter; 124 return ((tc->tc_get_timecount(tc) - th->th_offset_count) & 125 tc->tc_counter_mask); 126 } 127 128 /* 129 * Functions for reading the time. We have to loop until we are sure that 130 * the timehands that we operated on was not updated under our feet. See 131 * the comment in <sys/time.h> for a description of these 12 functions. 132 */ 133 134 void 135 binuptime(struct bintime *bt) 136 { 137 struct timehands *th; 138 u_int gen; 139 140 nbinuptime++; 141 do { 142 th = timehands; 143 gen = th->th_generation; 144 *bt = th->th_offset; 145 bintime_addx(bt, th->th_scale * tc_delta(th)); 146 } while (gen == 0 || gen != th->th_generation); 147 } 148 149 void 150 nanouptime(struct timespec *tsp) 151 { 152 struct bintime bt; 153 154 nnanouptime++; 155 binuptime(&bt); 156 bintime2timespec(&bt, tsp); 157 } 158 159 void 160 microuptime(struct timeval *tvp) 161 { 162 struct bintime bt; 163 164 nmicrouptime++; 165 binuptime(&bt); 166 bintime2timeval(&bt, tvp); 167 } 168 169 void 170 bintime(struct bintime *bt) 171 { 172 173 nbintime++; 174 binuptime(bt); 175 bintime_add(bt, &boottimebin); 176 } 177 178 void 179 nanotime(struct timespec *tsp) 180 { 181 struct bintime bt; 182 183 nnanotime++; 184 bintime(&bt); 185 bintime2timespec(&bt, tsp); 186 } 187 188 void 189 microtime(struct timeval *tvp) 190 { 191 struct bintime bt; 192 193 nmicrotime++; 194 bintime(&bt); 195 bintime2timeval(&bt, tvp); 196 } 197 198 void 199 getbinuptime(struct bintime *bt) 200 { 201 struct timehands *th; 202 u_int gen; 203 204 ngetbinuptime++; 205 do { 206 th = timehands; 207 gen = th->th_generation; 208 *bt = th->th_offset; 209 } while (gen == 0 || gen != th->th_generation); 210 } 211 212 void 213 getnanouptime(struct timespec *tsp) 214 { 215 struct timehands *th; 216 u_int gen; 217 218 ngetnanouptime++; 219 do { 220 th = timehands; 221 gen = th->th_generation; 222 bintime2timespec(&th->th_offset, tsp); 223 } while (gen == 0 || gen != th->th_generation); 224 } 225 226 void 227 getmicrouptime(struct timeval *tvp) 228 { 229 struct timehands *th; 230 u_int gen; 231 232 ngetmicrouptime++; 233 do { 234 th = timehands; 235 gen = th->th_generation; 236 bintime2timeval(&th->th_offset, tvp); 237 } while (gen == 0 || gen != th->th_generation); 238 } 239 240 void 241 getbintime(struct bintime *bt) 242 { 243 struct timehands *th; 244 u_int gen; 245 246 ngetbintime++; 247 do { 248 th = timehands; 249 gen = th->th_generation; 250 *bt = th->th_offset; 251 } while (gen == 0 || gen != th->th_generation); 252 bintime_add(bt, &boottimebin); 253 } 254 255 void 256 getnanotime(struct timespec *tsp) 257 { 258 struct timehands *th; 259 u_int gen; 260 261 ngetnanotime++; 262 do { 263 th = timehands; 264 gen = th->th_generation; 265 *tsp = th->th_nanotime; 266 } while (gen == 0 || gen != th->th_generation); 267 } 268 269 void 270 getmicrotime(struct timeval *tvp) 271 { 272 struct timehands *th; 273 u_int gen; 274 275 ngetmicrotime++; 276 do { 277 th = timehands; 278 gen = th->th_generation; 279 *tvp = th->th_microtime; 280 } while (gen == 0 || gen != th->th_generation); 281 } 282 283 /* 284 * Initialize a new timecounter and possibly use it. 285 */ 286 void 287 tc_init(struct timecounter *tc) 288 { 289 u_int u; 290 291 u = tc->tc_frequency / tc->tc_counter_mask; 292 /* XXX: We need some margin here, 10% is a guess */ 293 u *= 11; 294 u /= 10; 295 if (u > hz && tc->tc_quality >= 0) { 296 tc->tc_quality = -2000; 297 if (bootverbose) { 298 printf("Timecounter \"%s\" frequency %ju Hz", 299 tc->tc_name, (uintmax_t)tc->tc_frequency); 300 printf(" -- Insufficient hz, needs at least %u\n", u); 301 } 302 } else if (tc->tc_quality >= 0 || bootverbose) { 303 printf("Timecounter \"%s\" frequency %ju Hz quality %d\n", 304 tc->tc_name, (uintmax_t)tc->tc_frequency, 305 tc->tc_quality); 306 } 307 308 tc->tc_next = timecounters; 309 timecounters = tc; 310 /* 311 * Never automatically use a timecounter with negative quality. 312 * Even though we run on the dummy counter, switching here may be 313 * worse since this timecounter may not be monotonous. 314 */ 315 if (tc->tc_quality < 0) 316 return; 317 if (tc->tc_quality < timecounter->tc_quality) 318 return; 319 if (tc->tc_quality == timecounter->tc_quality && 320 tc->tc_frequency < timecounter->tc_frequency) 321 return; 322 (void)tc->tc_get_timecount(tc); 323 (void)tc->tc_get_timecount(tc); 324 timecounter = tc; 325 } 326 327 /* Report the frequency of the current timecounter. */ 328 u_int64_t 329 tc_getfrequency(void) 330 { 331 332 return (timehands->th_counter->tc_frequency); 333 } 334 335 /* 336 * Step our concept of UTC. This is done by modifying our estimate of 337 * when we booted. XXX: needs further work. 338 */ 339 void 340 tc_setclock(struct timespec *ts) 341 { 342 struct timespec ts2; 343 344 nsetclock++; 345 nanouptime(&ts2); 346 boottime.tv_sec = ts->tv_sec - ts2.tv_sec; 347 /* XXX boottime should probably be a timespec. */ 348 boottime.tv_usec = (ts->tv_nsec - ts2.tv_nsec) / 1000; 349 if (boottime.tv_usec < 0) { 350 boottime.tv_usec += 1000000; 351 boottime.tv_sec--; 352 } 353 timeval2bintime(&boottime, &boottimebin); 354 355 /* XXX fiddle all the little crinkly bits around the fiords... */ 356 tc_windup(); 357 } 358 359 /* 360 * Initialize the next struct timehands in the ring and make 361 * it the active timehands. Along the way we might switch to a different 362 * timecounter and/or do seconds processing in NTP. Slightly magic. 363 */ 364 static void 365 tc_windup(void) 366 { 367 struct bintime bt; 368 struct timehands *th, *tho; 369 u_int64_t scale; 370 u_int delta, ncount, ogen; 371 int i; 372 time_t t; 373 374 /* 375 * Make the next timehands a copy of the current one, but do not 376 * overwrite the generation or next pointer. While we update 377 * the contents, the generation must be zero. 378 */ 379 tho = timehands; 380 th = tho->th_next; 381 ogen = th->th_generation; 382 th->th_generation = 0; 383 bcopy(tho, th, offsetof(struct timehands, th_generation)); 384 385 /* 386 * Capture a timecounter delta on the current timecounter and if 387 * changing timecounters, a counter value from the new timecounter. 388 * Update the offset fields accordingly. 389 */ 390 delta = tc_delta(th); 391 if (th->th_counter != timecounter) 392 ncount = timecounter->tc_get_timecount(timecounter); 393 else 394 ncount = 0; 395 th->th_offset_count += delta; 396 th->th_offset_count &= th->th_counter->tc_counter_mask; 397 bintime_addx(&th->th_offset, th->th_scale * delta); 398 399 /* 400 * Hardware latching timecounters may not generate interrupts on 401 * PPS events, so instead we poll them. There is a finite risk that 402 * the hardware might capture a count which is later than the one we 403 * got above, and therefore possibly in the next NTP second which might 404 * have a different rate than the current NTP second. It doesn't 405 * matter in practice. 406 */ 407 if (tho->th_counter->tc_poll_pps) 408 tho->th_counter->tc_poll_pps(tho->th_counter); 409 410 /* 411 * Deal with NTP second processing. The for loop normally 412 * iterates at most once, but in extreme situations it might 413 * keep NTP sane if timeouts are not run for several seconds. 414 * At boot, the time step can be large when the TOD hardware 415 * has been read, so on really large steps, we call 416 * ntp_update_second only twice. We need to call it twice in 417 * case we missed a leap second. 418 */ 419 bt = th->th_offset; 420 bintime_add(&bt, &boottimebin); 421 i = bt.sec - tho->th_microtime.tv_sec; 422 if (i > LARGE_STEP) 423 i = 2; 424 for (; i > 0; i--) { 425 t = bt.sec; 426 ntp_update_second(&th->th_adjustment, &bt.sec); 427 if (bt.sec != t) 428 boottimebin.sec += bt.sec - t; 429 } 430 /* Update the UTC timestamps used by the get*() functions. */ 431 /* XXX shouldn't do this here. Should force non-`get' versions. */ 432 bintime2timeval(&bt, &th->th_microtime); 433 bintime2timespec(&bt, &th->th_nanotime); 434 435 /* Now is a good time to change timecounters. */ 436 if (th->th_counter != timecounter) { 437 th->th_counter = timecounter; 438 th->th_offset_count = ncount; 439 } 440 441 /*- 442 * Recalculate the scaling factor. We want the number of 1/2^64 443 * fractions of a second per period of the hardware counter, taking 444 * into account the th_adjustment factor which the NTP PLL/adjtime(2) 445 * processing provides us with. 446 * 447 * The th_adjustment is nanoseconds per second with 32 bit binary 448 * fraction and we want 64 bit binary fraction of second: 449 * 450 * x = a * 2^32 / 10^9 = a * 4.294967296 451 * 452 * The range of th_adjustment is +/- 5000PPM so inside a 64bit int 453 * we can only multiply by about 850 without overflowing, but that 454 * leaves suitably precise fractions for multiply before divide. 455 * 456 * Divide before multiply with a fraction of 2199/512 results in a 457 * systematic undercompensation of 10PPM of th_adjustment. On a 458 * 5000PPM adjustment this is a 0.05PPM error. This is acceptable. 459 * 460 * We happily sacrifice the lowest of the 64 bits of our result 461 * to the goddess of code clarity. 462 * 463 */ 464 scale = (u_int64_t)1 << 63; 465 scale += (th->th_adjustment / 1024) * 2199; 466 scale /= th->th_counter->tc_frequency; 467 th->th_scale = scale * 2; 468 469 /* 470 * Now that the struct timehands is again consistent, set the new 471 * generation number, making sure to not make it zero. 472 */ 473 if (++ogen == 0) 474 ogen = 1; 475 th->th_generation = ogen; 476 477 /* Go live with the new struct timehands. */ 478 time_second = th->th_microtime.tv_sec; 479 time_uptime = th->th_offset.sec; 480 timehands = th; 481 } 482 483 /* Report or change the active timecounter hardware. */ 484 static int 485 sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS) 486 { 487 char newname[32]; 488 struct timecounter *newtc, *tc; 489 int error; 490 491 tc = timecounter; 492 strlcpy(newname, tc->tc_name, sizeof(newname)); 493 494 error = sysctl_handle_string(oidp, &newname[0], sizeof(newname), req); 495 if (error != 0 || req->newptr == NULL || 496 strcmp(newname, tc->tc_name) == 0) 497 return (error); 498 for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) { 499 if (strcmp(newname, newtc->tc_name) != 0) 500 continue; 501 502 /* Warm up new timecounter. */ 503 (void)newtc->tc_get_timecount(newtc); 504 (void)newtc->tc_get_timecount(newtc); 505 506 timecounter = newtc; 507 return (0); 508 } 509 return (EINVAL); 510 } 511 512 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | CTLFLAG_RW, 513 0, 0, sysctl_kern_timecounter_hardware, "A", ""); 514 515 516 /* Report or change the active timecounter hardware. */ 517 static int 518 sysctl_kern_timecounter_choice(SYSCTL_HANDLER_ARGS) 519 { 520 char buf[32], *spc; 521 struct timecounter *tc; 522 int error; 523 524 spc = ""; 525 error = 0; 526 for (tc = timecounters; error == 0 && tc != NULL; tc = tc->tc_next) { 527 sprintf(buf, "%s%s(%d)", 528 spc, tc->tc_name, tc->tc_quality); 529 error = SYSCTL_OUT(req, buf, strlen(buf)); 530 spc = " "; 531 } 532 return (error); 533 } 534 535 SYSCTL_PROC(_kern_timecounter, OID_AUTO, choice, CTLTYPE_STRING | CTLFLAG_RD, 536 0, 0, sysctl_kern_timecounter_choice, "A", ""); 537 538 /* 539 * RFC 2783 PPS-API implementation. 540 */ 541 542 int 543 pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps) 544 { 545 pps_params_t *app; 546 struct pps_fetch_args *fapi; 547 #ifdef PPS_SYNC 548 struct pps_kcbind_args *kapi; 549 #endif 550 551 switch (cmd) { 552 case PPS_IOC_CREATE: 553 return (0); 554 case PPS_IOC_DESTROY: 555 return (0); 556 case PPS_IOC_SETPARAMS: 557 app = (pps_params_t *)data; 558 if (app->mode & ~pps->ppscap) 559 return (EINVAL); 560 pps->ppsparam = *app; 561 return (0); 562 case PPS_IOC_GETPARAMS: 563 app = (pps_params_t *)data; 564 *app = pps->ppsparam; 565 app->api_version = PPS_API_VERS_1; 566 return (0); 567 case PPS_IOC_GETCAP: 568 *(int*)data = pps->ppscap; 569 return (0); 570 case PPS_IOC_FETCH: 571 fapi = (struct pps_fetch_args *)data; 572 if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC) 573 return (EINVAL); 574 if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec) 575 return (EOPNOTSUPP); 576 pps->ppsinfo.current_mode = pps->ppsparam.mode; 577 fapi->pps_info_buf = pps->ppsinfo; 578 return (0); 579 case PPS_IOC_KCBIND: 580 #ifdef PPS_SYNC 581 kapi = (struct pps_kcbind_args *)data; 582 /* XXX Only root should be able to do this */ 583 if (kapi->tsformat && kapi->tsformat != PPS_TSFMT_TSPEC) 584 return (EINVAL); 585 if (kapi->kernel_consumer != PPS_KC_HARDPPS) 586 return (EINVAL); 587 if (kapi->edge & ~pps->ppscap) 588 return (EINVAL); 589 pps->kcmode = kapi->edge; 590 return (0); 591 #else 592 return (EOPNOTSUPP); 593 #endif 594 default: 595 return (ENOTTY); 596 } 597 } 598 599 void 600 pps_init(struct pps_state *pps) 601 { 602 pps->ppscap |= PPS_TSFMT_TSPEC; 603 if (pps->ppscap & PPS_CAPTUREASSERT) 604 pps->ppscap |= PPS_OFFSETASSERT; 605 if (pps->ppscap & PPS_CAPTURECLEAR) 606 pps->ppscap |= PPS_OFFSETCLEAR; 607 } 608 609 void 610 pps_capture(struct pps_state *pps) 611 { 612 struct timehands *th; 613 614 th = timehands; 615 pps->capgen = th->th_generation; 616 pps->capth = th; 617 pps->capcount = th->th_counter->tc_get_timecount(th->th_counter); 618 if (pps->capgen != th->th_generation) 619 pps->capgen = 0; 620 } 621 622 void 623 pps_event(struct pps_state *pps, int event) 624 { 625 struct bintime bt; 626 struct timespec ts, *tsp, *osp; 627 u_int tcount, *pcount; 628 int foff, fhard; 629 pps_seq_t *pseq; 630 631 /* If the timecounter was wound up underneath us, bail out. */ 632 if (pps->capgen == 0 || pps->capgen != pps->capth->th_generation) 633 return; 634 635 /* Things would be easier with arrays. */ 636 if (event == PPS_CAPTUREASSERT) { 637 tsp = &pps->ppsinfo.assert_timestamp; 638 osp = &pps->ppsparam.assert_offset; 639 foff = pps->ppsparam.mode & PPS_OFFSETASSERT; 640 fhard = pps->kcmode & PPS_CAPTUREASSERT; 641 pcount = &pps->ppscount[0]; 642 pseq = &pps->ppsinfo.assert_sequence; 643 } else { 644 tsp = &pps->ppsinfo.clear_timestamp; 645 osp = &pps->ppsparam.clear_offset; 646 foff = pps->ppsparam.mode & PPS_OFFSETCLEAR; 647 fhard = pps->kcmode & PPS_CAPTURECLEAR; 648 pcount = &pps->ppscount[1]; 649 pseq = &pps->ppsinfo.clear_sequence; 650 } 651 652 /* 653 * If the timecounter changed, we cannot compare the count values, so 654 * we have to drop the rest of the PPS-stuff until the next event. 655 */ 656 if (pps->ppstc != pps->capth->th_counter) { 657 pps->ppstc = pps->capth->th_counter; 658 *pcount = pps->capcount; 659 pps->ppscount[2] = pps->capcount; 660 return; 661 } 662 663 /* Return if nothing really happened. */ 664 if (*pcount == pps->capcount) 665 return; 666 667 /* Convert the count to a timespec. */ 668 tcount = pps->capcount - pps->capth->th_offset_count; 669 tcount &= pps->capth->th_counter->tc_counter_mask; 670 bt = pps->capth->th_offset; 671 bintime_addx(&bt, pps->capth->th_scale * tcount); 672 bintime_add(&bt, &boottimebin); 673 bintime2timespec(&bt, &ts); 674 675 /* If the timecounter was wound up underneath us, bail out. */ 676 if (pps->capgen != pps->capth->th_generation) 677 return; 678 679 *pcount = pps->capcount; 680 (*pseq)++; 681 *tsp = ts; 682 683 if (foff) { 684 timespecadd(tsp, osp); 685 if (tsp->tv_nsec < 0) { 686 tsp->tv_nsec += 1000000000; 687 tsp->tv_sec -= 1; 688 } 689 } 690 #ifdef PPS_SYNC 691 if (fhard) { 692 u_int64_t scale; 693 694 /* 695 * Feed the NTP PLL/FLL. 696 * The FLL wants to know how many (hardware) nanoseconds 697 * elapsed since the previous event. 698 */ 699 tcount = pps->capcount - pps->ppscount[2]; 700 pps->ppscount[2] = pps->capcount; 701 tcount &= pps->capth->th_counter->tc_counter_mask; 702 scale = (u_int64_t)1 << 63; 703 scale /= pps->capth->th_counter->tc_frequency; 704 scale *= 2; 705 bt.sec = 0; 706 bt.frac = 0; 707 bintime_addx(&bt, scale * tcount); 708 bintime2timespec(&bt, &ts); 709 hardpps(tsp, ts.tv_nsec + 1000000000 * ts.tv_sec); 710 } 711 #endif 712 } 713 714 /* 715 * Timecounters need to be updated every so often to prevent the hardware 716 * counter from overflowing. Updating also recalculates the cached values 717 * used by the get*() family of functions, so their precision depends on 718 * the update frequency. 719 */ 720 721 static int tc_tick; 722 SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tc_tick, 0, ""); 723 724 void 725 tc_ticktock(void) 726 { 727 static int count; 728 729 if (++count < tc_tick) 730 return; 731 count = 0; 732 tc_windup(); 733 } 734 735 static void 736 inittimecounter(void *dummy) 737 { 738 u_int p; 739 740 /* 741 * Set the initial timeout to 742 * max(1, <approx. number of hardclock ticks in a millisecond>). 743 * People should probably not use the sysctl to set the timeout 744 * to smaller than its inital value, since that value is the 745 * smallest reasonable one. If they want better timestamps they 746 * should use the non-"get"* functions. 747 */ 748 if (hz > 1000) 749 tc_tick = (hz + 500) / 1000; 750 else 751 tc_tick = 1; 752 p = (tc_tick * 1000000) / hz; 753 printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000); 754 755 /* warm up new timecounter (again) and get rolling. */ 756 (void)timecounter->tc_get_timecount(timecounter); 757 (void)timecounter->tc_get_timecount(timecounter); 758 } 759 760 SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_SECOND, inittimecounter, NULL)
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