2 * linux/kernel/time/timekeeping.c
4 * Kernel timekeeping code and accessor functions
6 * This code was moved from linux/kernel/timer.c.
7 * Please see that file for copyright and history logs.
11 #include <linux/module.h>
12 #include <linux/interrupt.h>
13 #include <linux/percpu.h>
14 #include <linux/init.h>
16 #include <linux/sysdev.h>
17 #include <linux/clocksource.h>
18 #include <linux/jiffies.h>
19 #include <linux/time.h>
20 #include <linux/tick.h>
24 * This read-write spinlock protects us from races in SMP while
25 * playing with xtime and avenrun.
27 __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
32 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
33 * for sub jiffie times) to get to monotonic time. Monotonic is pegged
34 * at zero at system boot time, so wall_to_monotonic will be negative,
35 * however, we will ALWAYS keep the tv_nsec part positive so we can use
36 * the usual normalization.
38 * wall_to_monotonic is moved after resume from suspend for the monotonic
39 * time not to jump. We need to add total_sleep_time to wall_to_monotonic
40 * to get the real boot based time offset.
42 * - wall_to_monotonic is no longer the boot time, getboottime must be
45 struct timespec xtime __attribute__ ((aligned (16)));
46 struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
47 static unsigned long total_sleep_time; /* seconds */
49 /* flag for if timekeeping is suspended */
50 int __read_mostly timekeeping_suspended;
52 static struct timespec xtime_cache __attribute__ ((aligned (16)));
53 void update_xtime_cache(u64 nsec)
56 timespec_add_ns(&xtime_cache, nsec);
59 struct clocksource *clock;
62 #ifdef CONFIG_GENERIC_TIME
64 * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
66 * private function, must hold xtime_lock lock when being
67 * called. Returns the number of nanoseconds since the
68 * last call to update_wall_time() (adjusted by NTP scaling)
70 static inline s64 __get_nsec_offset(void)
72 cycle_t cycle_now, cycle_delta;
75 /* read clocksource: */
76 cycle_now = clocksource_read(clock);
78 /* calculate the delta since the last update_wall_time: */
79 cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
81 /* convert to nanoseconds: */
82 ns_offset = cyc2ns(clock, cycle_delta);
88 * getnstimeofday - Returns the time of day in a timespec
89 * @ts: pointer to the timespec to be set
91 * Returns the time of day in a timespec.
93 void getnstimeofday(struct timespec *ts)
98 WARN_ON(timekeeping_suspended);
101 seq = read_seqbegin(&xtime_lock);
104 nsecs = __get_nsec_offset();
106 } while (read_seqretry(&xtime_lock, seq));
108 timespec_add_ns(ts, nsecs);
111 EXPORT_SYMBOL(getnstimeofday);
114 * do_gettimeofday - Returns the time of day in a timeval
115 * @tv: pointer to the timeval to be set
117 * NOTE: Users should be converted to using getnstimeofday()
119 void do_gettimeofday(struct timeval *tv)
123 getnstimeofday(&now);
124 tv->tv_sec = now.tv_sec;
125 tv->tv_usec = now.tv_nsec/1000;
128 EXPORT_SYMBOL(do_gettimeofday);
130 * do_settimeofday - Sets the time of day
131 * @tv: pointer to the timespec variable containing the new time
133 * Sets the time of day to the new time and update NTP and notify hrtimers
135 int do_settimeofday(struct timespec *tv)
138 time_t wtm_sec, sec = tv->tv_sec;
139 long wtm_nsec, nsec = tv->tv_nsec;
141 if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
144 write_seqlock_irqsave(&xtime_lock, flags);
146 nsec -= __get_nsec_offset();
148 wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
149 wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
151 set_normalized_timespec(&xtime, sec, nsec);
152 set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
153 update_xtime_cache(0);
158 update_vsyscall(&xtime, clock);
160 write_sequnlock_irqrestore(&xtime_lock, flags);
162 /* signal hrtimers about time change */
168 EXPORT_SYMBOL(do_settimeofday);
171 * change_clocksource - Swaps clocksources if a new one is available
173 * Accumulates current time interval and initializes new clocksource
175 static void change_clocksource(void)
177 struct clocksource *new;
181 new = clocksource_get_next();
187 now = clocksource_read(new);
188 nsec = __get_nsec_offset();
189 timespec_add_ns(&xtime, nsec);
192 clock->cycle_last = now;
195 clock->xtime_nsec = 0;
196 clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
201 * We're holding xtime lock and waking up klogd would deadlock
202 * us on enqueue. So no printing!
203 printk(KERN_INFO "Time: %s clocksource has been installed.\n",
208 static inline void change_clocksource(void) { }
209 static inline s64 __get_nsec_offset(void) { return 0; }
213 * timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
215 int timekeeping_valid_for_hres(void)
221 seq = read_seqbegin(&xtime_lock);
223 ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
225 } while (read_seqretry(&xtime_lock, seq));
231 * read_persistent_clock - Return time in seconds from the persistent clock.
233 * Weak dummy function for arches that do not yet support it.
234 * Returns seconds from epoch using the battery backed persistent clock.
235 * Returns zero if unsupported.
237 * XXX - Do be sure to remove it once all arches implement it.
239 unsigned long __attribute__((weak)) read_persistent_clock(void)
245 * timekeeping_init - Initializes the clocksource and common timekeeping values
247 void __init timekeeping_init(void)
250 unsigned long sec = read_persistent_clock();
252 write_seqlock_irqsave(&xtime_lock, flags);
256 clock = clocksource_get_next();
257 clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
258 clock->cycle_last = clocksource_read(clock);
262 set_normalized_timespec(&wall_to_monotonic,
263 -xtime.tv_sec, -xtime.tv_nsec);
264 update_xtime_cache(0);
265 total_sleep_time = 0;
266 write_sequnlock_irqrestore(&xtime_lock, flags);
269 /* time in seconds when suspend began */
270 static unsigned long timekeeping_suspend_time;
271 /* xtime offset when we went into suspend */
272 static s64 timekeeping_suspend_nsecs;
275 * timekeeping_resume - Resumes the generic timekeeping subsystem.
278 * This is for the generic clocksource timekeeping.
279 * xtime/wall_to_monotonic/jiffies/etc are
280 * still managed by arch specific suspend/resume code.
282 static int timekeeping_resume(struct sys_device *dev)
285 unsigned long now = read_persistent_clock();
287 clocksource_resume();
289 write_seqlock_irqsave(&xtime_lock, flags);
291 if (now && (now > timekeeping_suspend_time)) {
292 unsigned long sleep_length = now - timekeeping_suspend_time;
294 xtime.tv_sec += sleep_length;
295 wall_to_monotonic.tv_sec -= sleep_length;
296 total_sleep_time += sleep_length;
298 /* Make sure that we have the correct xtime reference */
299 timespec_add_ns(&xtime, timekeeping_suspend_nsecs);
300 update_xtime_cache(0);
301 /* re-base the last cycle value */
302 clock->cycle_last = 0;
303 clock->cycle_last = clocksource_read(clock);
305 timekeeping_suspended = 0;
306 write_sequnlock_irqrestore(&xtime_lock, flags);
308 touch_softlockup_watchdog();
310 clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
312 /* Resume hrtimers */
313 hres_timers_resume();
318 static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
322 timekeeping_suspend_time = read_persistent_clock();
324 write_seqlock_irqsave(&xtime_lock, flags);
325 /* Get the current xtime offset */
326 timekeeping_suspend_nsecs = __get_nsec_offset();
327 timekeeping_suspended = 1;
328 write_sequnlock_irqrestore(&xtime_lock, flags);
330 clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
335 /* sysfs resume/suspend bits for timekeeping */
336 static struct sysdev_class timekeeping_sysclass = {
337 .name = "timekeeping",
338 .resume = timekeeping_resume,
339 .suspend = timekeeping_suspend,
342 static struct sys_device device_timer = {
344 .cls = &timekeeping_sysclass,
347 static int __init timekeeping_init_device(void)
349 int error = sysdev_class_register(&timekeeping_sysclass);
351 error = sysdev_register(&device_timer);
355 device_initcall(timekeeping_init_device);
358 * If the error is already larger, we look ahead even further
359 * to compensate for late or lost adjustments.
361 static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
369 * Use the current error value to determine how much to look ahead.
370 * The larger the error the slower we adjust for it to avoid problems
371 * with losing too many ticks, otherwise we would overadjust and
372 * produce an even larger error. The smaller the adjustment the
373 * faster we try to adjust for it, as lost ticks can do less harm
374 * here. This is tuned so that an error of about 1 msec is adjusted
375 * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
377 error2 = clock->error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
378 error2 = abs(error2);
379 for (look_ahead = 0; error2 > 0; look_ahead++)
383 * Now calculate the error in (1 << look_ahead) ticks, but first
384 * remove the single look ahead already included in the error.
386 tick_error = tick_length >> (NTP_SCALE_SHIFT - clock->shift + 1);
387 tick_error -= clock->xtime_interval >> 1;
388 error = ((error - tick_error) >> look_ahead) + tick_error;
390 /* Finally calculate the adjustment shift value. */
395 *interval = -*interval;
399 for (adj = 0; error > i; adj++)
408 * Adjust the multiplier to reduce the error value,
409 * this is optimized for the most common adjustments of -1,0,1,
410 * for other values we can do a bit more work.
412 static void clocksource_adjust(s64 offset)
414 s64 error, interval = clock->cycle_interval;
417 error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
418 if (error > interval) {
420 if (likely(error <= interval))
423 adj = clocksource_bigadjust(error, &interval, &offset);
424 } else if (error < -interval) {
426 if (likely(error >= -interval)) {
428 interval = -interval;
431 adj = clocksource_bigadjust(error, &interval, &offset);
436 clock->xtime_interval += interval;
437 clock->xtime_nsec -= offset;
438 clock->error -= (interval - offset) <<
439 (NTP_SCALE_SHIFT - clock->shift);
443 * update_wall_time - Uses the current clocksource to increment the wall time
445 * Called from the timer interrupt, must hold a write on xtime_lock.
447 void update_wall_time(void)
451 /* Make sure we're fully resumed: */
452 if (unlikely(timekeeping_suspended))
455 #ifdef CONFIG_GENERIC_TIME
456 offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
458 offset = clock->cycle_interval;
460 clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;
462 /* normally this loop will run just once, however in the
463 * case of lost or late ticks, it will accumulate correctly.
465 while (offset >= clock->cycle_interval) {
466 /* accumulate one interval */
467 clock->xtime_nsec += clock->xtime_interval;
468 clock->cycle_last += clock->cycle_interval;
469 offset -= clock->cycle_interval;
471 if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
472 clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
477 /* accumulate error between NTP and clock interval */
478 clock->error += tick_length;
479 clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
482 /* correct the clock when NTP error is too big */
483 clocksource_adjust(offset);
485 /* store full nanoseconds into xtime */
486 xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
487 clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
489 update_xtime_cache(cyc2ns(clock, offset));
491 /* check to see if there is a new clocksource to use */
492 change_clocksource();
493 update_vsyscall(&xtime, clock);
497 * getboottime - Return the real time of system boot.
498 * @ts: pointer to the timespec to be set
500 * Returns the time of day in a timespec.
502 * This is based on the wall_to_monotonic offset and the total suspend
503 * time. Calls to settimeofday will affect the value returned (which
504 * basically means that however wrong your real time clock is at boot time,
505 * you get the right time here).
507 void getboottime(struct timespec *ts)
509 set_normalized_timespec(ts,
510 - (wall_to_monotonic.tv_sec + total_sleep_time),
511 - wall_to_monotonic.tv_nsec);
515 * monotonic_to_bootbased - Convert the monotonic time to boot based.
516 * @ts: pointer to the timespec to be converted
518 void monotonic_to_bootbased(struct timespec *ts)
520 ts->tv_sec += total_sleep_time;
523 unsigned long get_seconds(void)
525 return xtime_cache.tv_sec;
527 EXPORT_SYMBOL(get_seconds);
530 struct timespec current_kernel_time(void)
536 seq = read_seqbegin(&xtime_lock);
539 } while (read_seqretry(&xtime_lock, seq));
543 EXPORT_SYMBOL(current_kernel_time);