/*- * ---------------------------------------------------------------------------- * "THE BEER-WARE LICENSE" (Revision 42): * wrote this file. As long as you retain this notice you * can do whatever you want with this stuff. If we meet some day, and you think * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp * ---------------------------------------------------------------------------- */ #include __FBSDID("$FreeBSD$"); #include "opt_ntp.h" #include #include #include #include #include #include #include #include /* * A large step happens on boot. This constant detects such steps. * It is relatively small so that ntp_update_second gets called enough * in the typical 'missed a couple of seconds' case, but doesn't loop * forever when the time step is large. */ #define LARGE_STEP 200 /* * Implement a dummy timecounter which we can use until we get a real one * in the air. This allows the console and other early stuff to use * time services. */ static u_int dummy_get_timecount(struct timecounter *tc) { static u_int now; return (++now); } static struct timecounter dummy_timecounter = { dummy_get_timecount, 0, ~0u, 1000000, "dummy", -1000000 }; struct timehands { /* These fields must be initialized by the driver. */ struct timecounter *th_counter; int64_t th_adjustment; u_int64_t th_scale; u_int th_offset_count; struct bintime th_offset; struct timeval th_microtime; struct timespec th_nanotime; /* Fields not to be copied in tc_windup start with th_generation. */ volatile u_int th_generation; struct timehands *th_next; }; static struct timehands th0; static struct timehands th9 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th0}; static struct timehands th8 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th9}; static struct timehands th7 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th8}; static struct timehands th6 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th7}; static struct timehands th5 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th6}; static struct timehands th4 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th5}; static struct timehands th3 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th4}; static struct timehands th2 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th3}; static struct timehands th1 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th2}; static struct timehands th0 = { &dummy_timecounter, 0, (uint64_t)-1 / 1000000, 0, {1, 0}, {0, 0}, {0, 0}, 1, &th1 }; static struct timehands *volatile timehands = &th0; struct timecounter *timecounter = &dummy_timecounter; static struct timecounter *timecounters = &dummy_timecounter; time_t time_second = 1; time_t time_uptime = 1; static struct bintime boottimebin; struct timeval boottime; static int sysctl_kern_boottime(SYSCTL_HANDLER_ARGS); SYSCTL_PROC(_kern, KERN_BOOTTIME, boottime, CTLTYPE_STRUCT|CTLFLAG_RD, NULL, 0, sysctl_kern_boottime, "S,timeval", "System boottime"); SYSCTL_NODE(_kern, OID_AUTO, timecounter, CTLFLAG_RW, 0, ""); static int timestepwarnings; SYSCTL_INT(_kern_timecounter, OID_AUTO, stepwarnings, CTLFLAG_RW, ×tepwarnings, 0, ""); #define TC_STATS(foo) \ static u_int foo; \ SYSCTL_UINT(_kern_timecounter, OID_AUTO, foo, CTLFLAG_RD, &foo, 0, "");\ struct __hack TC_STATS(nbinuptime); TC_STATS(nnanouptime); TC_STATS(nmicrouptime); TC_STATS(nbintime); TC_STATS(nnanotime); TC_STATS(nmicrotime); TC_STATS(ngetbinuptime); TC_STATS(ngetnanouptime); TC_STATS(ngetmicrouptime); TC_STATS(ngetbintime); TC_STATS(ngetnanotime); TC_STATS(ngetmicrotime); TC_STATS(nsetclock); #undef TC_STATS static void tc_windup(void); static void cpu_tick_calibrate(int); static int sysctl_kern_boottime(SYSCTL_HANDLER_ARGS) { #ifdef SCTL_MASK32 int tv[2]; if (req->flags & SCTL_MASK32) { tv[0] = boottime.tv_sec; tv[1] = boottime.tv_usec; return SYSCTL_OUT(req, tv, sizeof(tv)); } else #endif return SYSCTL_OUT(req, &boottime, sizeof(boottime)); } /* * Return the difference between the timehands' counter value now and what * was when we copied it to the timehands' offset_count. */ static __inline u_int tc_delta(struct timehands *th) { struct timecounter *tc; tc = th->th_counter; return ((tc->tc_get_timecount(tc) - th->th_offset_count) & tc->tc_counter_mask); } /* * Functions for reading the time. We have to loop until we are sure that * the timehands that we operated on was not updated under our feet. See * the comment in for a description of these 12 functions. */ void binuptime(struct bintime *bt) { struct timehands *th; u_int gen; nbinuptime++; do { th = timehands; gen = th->th_generation; *bt = th->th_offset; bintime_addx(bt, th->th_scale * tc_delta(th)); } while (gen == 0 || gen != th->th_generation); } void nanouptime(struct timespec *tsp) { struct bintime bt; nnanouptime++; binuptime(&bt); bintime2timespec(&bt, tsp); } void microuptime(struct timeval *tvp) { struct bintime bt; nmicrouptime++; binuptime(&bt); bintime2timeval(&bt, tvp); } void bintime(struct bintime *bt) { nbintime++; binuptime(bt); bintime_add(bt, &boottimebin); } void nanotime(struct timespec *tsp) { struct bintime bt; nnanotime++; bintime(&bt); bintime2timespec(&bt, tsp); } void microtime(struct timeval *tvp) { struct bintime bt; nmicrotime++; bintime(&bt); bintime2timeval(&bt, tvp); } void getbinuptime(struct bintime *bt) { struct timehands *th; u_int gen; ngetbinuptime++; do { th = timehands; gen = th->th_generation; *bt = th->th_offset; } while (gen == 0 || gen != th->th_generation); } void getnanouptime(struct timespec *tsp) { struct timehands *th; u_int gen; ngetnanouptime++; do { th = timehands; gen = th->th_generation; bintime2timespec(&th->th_offset, tsp); } while (gen == 0 || gen != th->th_generation); } void getmicrouptime(struct timeval *tvp) { struct timehands *th; u_int gen; ngetmicrouptime++; do { th = timehands; gen = th->th_generation; bintime2timeval(&th->th_offset, tvp); } while (gen == 0 || gen != th->th_generation); } void getbintime(struct bintime *bt) { struct timehands *th; u_int gen; ngetbintime++; do { th = timehands; gen = th->th_generation; *bt = th->th_offset; } while (gen == 0 || gen != th->th_generation); bintime_add(bt, &boottimebin); } void getnanotime(struct timespec *tsp) { struct timehands *th; u_int gen; ngetnanotime++; do { th = timehands; gen = th->th_generation; *tsp = th->th_nanotime; } while (gen == 0 || gen != th->th_generation); } void getmicrotime(struct timeval *tvp) { struct timehands *th; u_int gen; ngetmicrotime++; do { th = timehands; gen = th->th_generation; *tvp = th->th_microtime; } while (gen == 0 || gen != th->th_generation); } /* * Initialize a new timecounter and possibly use it. */ void tc_init(struct timecounter *tc) { u_int u; u = tc->tc_frequency / tc->tc_counter_mask; /* XXX: We need some margin here, 10% is a guess */ u *= 11; u /= 10; if (u > hz && tc->tc_quality >= 0) { tc->tc_quality = -2000; if (bootverbose) { printf("Timecounter \"%s\" frequency %ju Hz", tc->tc_name, (uintmax_t)tc->tc_frequency); printf(" -- Insufficient hz, needs at least %u\n", u); } } else if (tc->tc_quality >= 0 || bootverbose) { printf("Timecounter \"%s\" frequency %ju Hz quality %d\n", tc->tc_name, (uintmax_t)tc->tc_frequency, tc->tc_quality); } tc->tc_next = timecounters; timecounters = tc; /* * Never automatically use a timecounter with negative quality. * Even though we run on the dummy counter, switching here may be * worse since this timecounter may not be monotonous. */ if (tc->tc_quality < 0) return; if (tc->tc_quality < timecounter->tc_quality) return; if (tc->tc_quality == timecounter->tc_quality && tc->tc_frequency < timecounter->tc_frequency) return; (void)tc->tc_get_timecount(tc); (void)tc->tc_get_timecount(tc); timecounter = tc; } /* Report the frequency of the current timecounter. */ u_int64_t tc_getfrequency(void) { return (timehands->th_counter->tc_frequency); } /* * Step our concept of UTC. This is done by modifying our estimate of * when we booted. * XXX: not locked. */ void tc_setclock(struct timespec *ts) { struct timespec tbef, taft; struct bintime bt, bt2; cpu_tick_calibrate(1); nsetclock++; nanotime(&tbef); timespec2bintime(ts, &bt); binuptime(&bt2); bintime_sub(&bt, &bt2); bintime_add(&bt2, &boottimebin); boottimebin = bt; bintime2timeval(&bt, &boottime); /* XXX fiddle all the little crinkly bits around the fiords... */ tc_windup(); nanotime(&taft); if (timestepwarnings) { log(LOG_INFO, "Time stepped from %jd.%09ld to %jd.%09ld (%jd.%09ld)\n", (intmax_t)tbef.tv_sec, tbef.tv_nsec, (intmax_t)taft.tv_sec, taft.tv_nsec, (intmax_t)ts->tv_sec, ts->tv_nsec); } cpu_tick_calibrate(1); } /* * Initialize the next struct timehands in the ring and make * it the active timehands. Along the way we might switch to a different * timecounter and/or do seconds processing in NTP. Slightly magic. */ static void tc_windup(void) { struct bintime bt; struct timehands *th, *tho; u_int64_t scale; u_int delta, ncount, ogen; int i; time_t t; /* * Make the next timehands a copy of the current one, but do not * overwrite the generation or next pointer. While we update * the contents, the generation must be zero. */ tho = timehands; th = tho->th_next; ogen = th->th_generation; th->th_generation = 0; bcopy(tho, th, offsetof(struct timehands, th_generation)); /* * Capture a timecounter delta on the current timecounter and if * changing timecounters, a counter value from the new timecounter. * Update the offset fields accordingly. */ delta = tc_delta(th); if (th->th_counter != timecounter) ncount = timecounter->tc_get_timecount(timecounter); else ncount = 0; th->th_offset_count += delta; th->th_offset_count &= th->th_counter->tc_counter_mask; bintime_addx(&th->th_offset, th->th_scale * delta); /* * Hardware latching timecounters may not generate interrupts on * PPS events, so instead we poll them. There is a finite risk that * the hardware might capture a count which is later than the one we * got above, and therefore possibly in the next NTP second which might * have a different rate than the current NTP second. It doesn't * matter in practice. */ if (tho->th_counter->tc_poll_pps) tho->th_counter->tc_poll_pps(tho->th_counter); /* * Deal with NTP second processing. The for loop normally * iterates at most once, but in extreme situations it might * keep NTP sane if timeouts are not run for several seconds. * At boot, the time step can be large when the TOD hardware * has been read, so on really large steps, we call * ntp_update_second only twice. We need to call it twice in * case we missed a leap second. */ bt = th->th_offset; bintime_add(&bt, &boottimebin); i = bt.sec - tho->th_microtime.tv_sec; if (i > LARGE_STEP) i = 2; for (; i > 0; i--) { t = bt.sec; ntp_update_second(&th->th_adjustment, &bt.sec); if (bt.sec != t) boottimebin.sec += bt.sec - t; } /* Update the UTC timestamps used by the get*() functions. */ /* XXX shouldn't do this here. Should force non-`get' versions. */ bintime2timeval(&bt, &th->th_microtime); bintime2timespec(&bt, &th->th_nanotime); /* Now is a good time to change timecounters. */ if (th->th_counter != timecounter) { th->th_counter = timecounter; th->th_offset_count = ncount; } /*- * Recalculate the scaling factor. We want the number of 1/2^64 * fractions of a second per period of the hardware counter, taking * into account the th_adjustment factor which the NTP PLL/adjtime(2) * processing provides us with. * * The th_adjustment is nanoseconds per second with 32 bit binary * fraction and we want 64 bit binary fraction of second: * * x = a * 2^32 / 10^9 = a * 4.294967296 * * The range of th_adjustment is +/- 5000PPM so inside a 64bit int * we can only multiply by about 850 without overflowing, that * leaves no suitably precise fractions for multiply before divide. * * Divide before multiply with a fraction of 2199/512 results in a * systematic undercompensation of 10PPM of th_adjustment. On a * 5000PPM adjustment this is a 0.05PPM error. This is acceptable. * * We happily sacrifice the lowest of the 64 bits of our result * to the goddess of code clarity. * */ scale = (u_int64_t)1 << 63; scale += (th->th_adjustment / 1024) * 2199; scale /= th->th_counter->tc_frequency; th->th_scale = scale * 2; /* * Now that the struct timehands is again consistent, set the new * generation number, making sure to not make it zero. */ if (++ogen == 0) ogen = 1; th->th_generation = ogen; /* Go live with the new struct timehands. */ time_second = th->th_microtime.tv_sec; time_uptime = th->th_offset.sec; timehands = th; } /* Report or change the active timecounter hardware. */ static int sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS) { char newname[32]; struct timecounter *newtc, *tc; int error; tc = timecounter; strlcpy(newname, tc->tc_name, sizeof(newname)); error = sysctl_handle_string(oidp, &newname[0], sizeof(newname), req); if (error != 0 || req->newptr == NULL || strcmp(newname, tc->tc_name) == 0) return (error); for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) { if (strcmp(newname, newtc->tc_name) != 0) continue; /* Warm up new timecounter. */ (void)newtc->tc_get_timecount(newtc); (void)newtc->tc_get_timecount(newtc); timecounter = newtc; return (0); } return (EINVAL); } SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | CTLFLAG_RW, 0, 0, sysctl_kern_timecounter_hardware, "A", ""); /* Report or change the active timecounter hardware. */ static int sysctl_kern_timecounter_choice(SYSCTL_HANDLER_ARGS) { char buf[32], *spc; struct timecounter *tc; int error; spc = ""; error = 0; for (tc = timecounters; error == 0 && tc != NULL; tc = tc->tc_next) { sprintf(buf, "%s%s(%d)", spc, tc->tc_name, tc->tc_quality); error = SYSCTL_OUT(req, buf, strlen(buf)); spc = " "; } return (error); } SYSCTL_PROC(_kern_timecounter, OID_AUTO, choice, CTLTYPE_STRING | CTLFLAG_RD, 0, 0, sysctl_kern_timecounter_choice, "A", ""); /* * RFC 2783 PPS-API implementation. */ int pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps) { pps_params_t *app; struct pps_fetch_args *fapi; #ifdef PPS_SYNC struct pps_kcbind_args *kapi; #endif KASSERT(pps != NULL, ("NULL pps pointer in pps_ioctl")); switch (cmd) { case PPS_IOC_CREATE: return (0); case PPS_IOC_DESTROY: return (0); case PPS_IOC_SETPARAMS: app = (pps_params_t *)data; if (app->mode & ~pps->ppscap) return (EINVAL); pps->ppsparam = *app; return (0); case PPS_IOC_GETPARAMS: app = (pps_params_t *)data; *app = pps->ppsparam; app->api_version = PPS_API_VERS_1; return (0); case PPS_IOC_GETCAP: *(int*)data = pps->ppscap; return (0); case PPS_IOC_FETCH: fapi = (struct pps_fetch_args *)data; if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC) return (EINVAL); if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec) return (EOPNOTSUPP); pps->ppsinfo.current_mode = pps->ppsparam.mode; fapi->pps_info_buf = pps->ppsinfo; return (0); case PPS_IOC_KCBIND: #ifdef PPS_SYNC kapi = (struct pps_kcbind_args *)data; /* XXX Only root should be able to do this */ if (kapi->tsformat && kapi->tsformat != PPS_TSFMT_TSPEC) return (EINVAL); if (kapi->kernel_consumer != PPS_KC_HARDPPS) return (EINVAL); if (kapi->edge & ~pps->ppscap) return (EINVAL); pps->kcmode = kapi->edge; return (0); #else return (EOPNOTSUPP); #endif default: return (ENOIOCTL); } } void pps_init(struct pps_state *pps) { pps->ppscap |= PPS_TSFMT_TSPEC; if (pps->ppscap & PPS_CAPTUREASSERT) pps->ppscap |= PPS_OFFSETASSERT; if (pps->ppscap & PPS_CAPTURECLEAR) pps->ppscap |= PPS_OFFSETCLEAR; } void pps_capture(struct pps_state *pps) { struct timehands *th; KASSERT(pps != NULL, ("NULL pps pointer in pps_capture")); th = timehands; pps->capgen = th->th_generation; pps->capth = th; pps->capcount = th->th_counter->tc_get_timecount(th->th_counter); if (pps->capgen != th->th_generation) pps->capgen = 0; } void pps_event(struct pps_state *pps, int event) { struct bintime bt; struct timespec ts, *tsp, *osp; u_int tcount, *pcount; int foff, fhard; pps_seq_t *pseq; KASSERT(pps != NULL, ("NULL pps pointer in pps_event")); /* If the timecounter was wound up underneath us, bail out. */ if (pps->capgen == 0 || pps->capgen != pps->capth->th_generation) return; /* Things would be easier with arrays. */ if (event == PPS_CAPTUREASSERT) { tsp = &pps->ppsinfo.assert_timestamp; osp = &pps->ppsparam.assert_offset; foff = pps->ppsparam.mode & PPS_OFFSETASSERT; fhard = pps->kcmode & PPS_CAPTUREASSERT; pcount = &pps->ppscount[0]; pseq = &pps->ppsinfo.assert_sequence; } else { tsp = &pps->ppsinfo.clear_timestamp; osp = &pps->ppsparam.clear_offset; foff = pps->ppsparam.mode & PPS_OFFSETCLEAR; fhard = pps->kcmode & PPS_CAPTURECLEAR; pcount = &pps->ppscount[1]; pseq = &pps->ppsinfo.clear_sequence; } /* * If the timecounter changed, we cannot compare the count values, so * we have to drop the rest of the PPS-stuff until the next event. */ if (pps->ppstc != pps->capth->th_counter) { pps->ppstc = pps->capth->th_counter; *pcount = pps->capcount; pps->ppscount[2] = pps->capcount; return; } /* Convert the count to a timespec. */ tcount = pps->capcount - pps->capth->th_offset_count; tcount &= pps->capth->th_counter->tc_counter_mask; bt = pps->capth->th_offset; bintime_addx(&bt, pps->capth->th_scale * tcount); bintime_add(&bt, &boottimebin); bintime2timespec(&bt, &ts); /* If the timecounter was wound up underneath us, bail out. */ if (pps->capgen != pps->capth->th_generation) return; *pcount = pps->capcount; (*pseq)++; *tsp = ts; if (foff) { timespecadd(tsp, osp); if (tsp->tv_nsec < 0) { tsp->tv_nsec += 1000000000; tsp->tv_sec -= 1; } } #ifdef PPS_SYNC if (fhard) { u_int64_t scale; /* * Feed the NTP PLL/FLL. * The FLL wants to know how many (hardware) nanoseconds * elapsed since the previous event. */ tcount = pps->capcount - pps->ppscount[2]; pps->ppscount[2] = pps->capcount; tcount &= pps->capth->th_counter->tc_counter_mask; scale = (u_int64_t)1 << 63; scale /= pps->capth->th_counter->tc_frequency; scale *= 2; bt.sec = 0; bt.frac = 0; bintime_addx(&bt, scale * tcount); bintime2timespec(&bt, &ts); hardpps(tsp, ts.tv_nsec + 1000000000 * ts.tv_sec); } #endif } /* * Timecounters need to be updated every so often to prevent the hardware * counter from overflowing. Updating also recalculates the cached values * used by the get*() family of functions, so their precision depends on * the update frequency. */ static int tc_tick; SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tc_tick, 0, ""); void tc_ticktock(void) { static int count; static time_t last_calib; if (++count < tc_tick) return; count = 0; tc_windup(); if (time_uptime != last_calib && !(time_uptime & 0xf)) { cpu_tick_calibrate(0); last_calib = time_uptime; } } static void inittimecounter(void *dummy) { u_int p; /* * Set the initial timeout to * max(1, ). * People should probably not use the sysctl to set the timeout * to smaller than its inital value, since that value is the * smallest reasonable one. If they want better timestamps they * should use the non-"get"* functions. */ if (hz > 1000) tc_tick = (hz + 500) / 1000; else tc_tick = 1; p = (tc_tick * 1000000) / hz; printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000); /* warm up new timecounter (again) and get rolling. */ (void)timecounter->tc_get_timecount(timecounter); (void)timecounter->tc_get_timecount(timecounter); } SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_SECOND, inittimecounter, NULL) /* Cpu tick handling -------------------------------------------------*/ static int cpu_tick_variable; static uint64_t cpu_tick_frequency; static uint64_t tc_cpu_ticks(void) { static uint64_t base; static unsigned last; unsigned u; struct timecounter *tc; tc = timehands->th_counter; u = tc->tc_get_timecount(tc) & tc->tc_counter_mask; if (u < last) base += (uint64_t)tc->tc_counter_mask + 1; last = u; return (u + base); } /* * This function gets called ever 16 seconds on only one designated * CPU in the system from hardclock() via tc_ticktock(). * * Whenever the real time clock is stepped we get called with reset=1 * to make sure we handle suspend/resume and similar events correctly. */ static void cpu_tick_calibrate(int reset) { static uint64_t c_last; uint64_t c_this, c_delta; static struct bintime t_last; struct bintime t_this, t_delta; uint32_t divi; if (reset) { /* The clock was stepped, abort & reset */ t_last.sec = 0; return; } /* we don't calibrate fixed rate cputicks */ if (!cpu_tick_variable) return; getbinuptime(&t_this); c_this = cpu_ticks(); if (t_last.sec != 0) { c_delta = c_this - c_last; t_delta = t_this; bintime_sub(&t_delta, &t_last); /* * Validate that 16 +/- 1/256 seconds passed. * After division by 16 this gives us a precision of * roughly 250PPM which is sufficient */ if (t_delta.sec > 16 || ( t_delta.sec == 16 && t_delta.frac >= (0x01LL << 56))) { /* too long */ if (bootverbose) printf("%ju.%016jx too long\n", (uintmax_t)t_delta.sec, (uintmax_t)t_delta.frac); } else if (t_delta.sec < 15 || (t_delta.sec == 15 && t_delta.frac <= (0xffLL << 56))) { /* too short */ if (bootverbose) printf("%ju.%016jx too short\n", (uintmax_t)t_delta.sec, (uintmax_t)t_delta.frac); } else { /* just right */ /* * Headroom: * 2^(64-20) / 16[s] = * 2^(44) / 16[s] = * 17.592.186.044.416 / 16 = * 1.099.511.627.776 [Hz] */ divi = t_delta.sec << 20; divi |= t_delta.frac >> (64 - 20); c_delta <<= 20; c_delta /= divi; if (c_delta > cpu_tick_frequency) { if (0 && bootverbose) printf("cpu_tick increased to %ju Hz\n", c_delta); cpu_tick_frequency = c_delta; } } } c_last = c_this; t_last = t_this; } void set_cputicker(cpu_tick_f *func, uint64_t freq, unsigned var) { if (func == NULL) { cpu_ticks = tc_cpu_ticks; } else { cpu_tick_frequency = freq; cpu_tick_variable = var; cpu_ticks = func; } } uint64_t cpu_tickrate(void) { if (cpu_ticks == tc_cpu_ticks) return (tc_getfrequency()); return (cpu_tick_frequency); } /* * We need to be slightly careful converting cputicks to microseconds. * There is plenty of margin in 64 bits of microseconds (half a million * years) and in 64 bits at 4 GHz (146 years), but if we do a multiply * before divide conversion (to retain precision) we find that the * margin shrinks to 1.5 hours (one millionth of 146y). * With a three prong approach we never loose significant bits, no * matter what the cputick rate and length of timeinterval is. */ uint64_t cputick2usec(uint64_t tick) { if (tick > 18446744073709551LL) /* floor(2^64 / 1000) */ return (tick / (cpu_tickrate() / 1000000LL)); else if (tick > 18446744073709LL) /* floor(2^64 / 1000000) */ return ((tick * 1000LL) / (cpu_tickrate() / 1000LL)); else return ((tick * 1000000LL) / cpu_tickrate()); } cpu_tick_f *cpu_ticks = tc_cpu_ticks;