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 * clocksource_forward_now - update clock to the current time
66 * Forward the current clock to update its state since the last call to
67 * update_wall_time(). This is useful before significant clock changes,
68 * as it avoids having to deal with this time offset explicitly.
70 static void clocksource_forward_now(void)
72 cycle_t cycle_now
, cycle_delta
;
75 cycle_now
= clocksource_read(clock
);
76 cycle_delta
= (cycle_now
- clock
->cycle_last
) & clock
->mask
;
77 clock
->cycle_last
= cycle_now
;
79 nsec
= cyc2ns(clock
, cycle_delta
);
80 timespec_add_ns(&xtime
, nsec
);
84 * getnstimeofday - Returns the time of day in a timespec
85 * @ts: pointer to the timespec to be set
87 * Returns the time of day in a timespec.
89 void getnstimeofday(struct timespec
*ts
)
91 cycle_t cycle_now
, cycle_delta
;
95 WARN_ON(timekeeping_suspended
);
98 seq
= read_seqbegin(&xtime_lock
);
102 /* read clocksource: */
103 cycle_now
= clocksource_read(clock
);
105 /* calculate the delta since the last update_wall_time: */
106 cycle_delta
= (cycle_now
- clock
->cycle_last
) & clock
->mask
;
108 /* convert to nanoseconds: */
109 nsecs
= cyc2ns(clock
, cycle_delta
);
111 } while (read_seqretry(&xtime_lock
, seq
));
113 timespec_add_ns(ts
, nsecs
);
116 EXPORT_SYMBOL(getnstimeofday
);
119 * do_gettimeofday - Returns the time of day in a timeval
120 * @tv: pointer to the timeval to be set
122 * NOTE: Users should be converted to using getnstimeofday()
124 void do_gettimeofday(struct timeval
*tv
)
128 getnstimeofday(&now
);
129 tv
->tv_sec
= now
.tv_sec
;
130 tv
->tv_usec
= now
.tv_nsec
/1000;
133 EXPORT_SYMBOL(do_gettimeofday
);
135 * do_settimeofday - Sets the time of day
136 * @tv: pointer to the timespec variable containing the new time
138 * Sets the time of day to the new time and update NTP and notify hrtimers
140 int do_settimeofday(struct timespec
*tv
)
142 struct timespec ts_delta
;
145 if ((unsigned long)tv
->tv_nsec
>= NSEC_PER_SEC
)
148 write_seqlock_irqsave(&xtime_lock
, flags
);
150 clocksource_forward_now();
152 ts_delta
.tv_sec
= tv
->tv_sec
- xtime
.tv_sec
;
153 ts_delta
.tv_nsec
= tv
->tv_nsec
- xtime
.tv_nsec
;
154 wall_to_monotonic
= timespec_sub(wall_to_monotonic
, ts_delta
);
158 update_xtime_cache(0);
163 update_vsyscall(&xtime
, clock
);
165 write_sequnlock_irqrestore(&xtime_lock
, flags
);
167 /* signal hrtimers about time change */
173 EXPORT_SYMBOL(do_settimeofday
);
176 * change_clocksource - Swaps clocksources if a new one is available
178 * Accumulates current time interval and initializes new clocksource
180 static void change_clocksource(void)
182 struct clocksource
*new;
184 new = clocksource_get_next();
189 clocksource_forward_now();
192 clock
->cycle_last
= 0;
193 clock
->cycle_last
= clocksource_read(new);
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 clocksource_forward_now(void) { }
209 static inline void change_clocksource(void) { }
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
;
273 * timekeeping_resume - Resumes the generic timekeeping subsystem.
276 * This is for the generic clocksource timekeeping.
277 * xtime/wall_to_monotonic/jiffies/etc are
278 * still managed by arch specific suspend/resume code.
280 static int timekeeping_resume(struct sys_device
*dev
)
283 unsigned long now
= read_persistent_clock();
285 clocksource_resume();
287 write_seqlock_irqsave(&xtime_lock
, flags
);
289 if (now
&& (now
> timekeeping_suspend_time
)) {
290 unsigned long sleep_length
= now
- timekeeping_suspend_time
;
292 xtime
.tv_sec
+= sleep_length
;
293 wall_to_monotonic
.tv_sec
-= sleep_length
;
294 total_sleep_time
+= sleep_length
;
296 update_xtime_cache(0);
297 /* re-base the last cycle value */
298 clock
->cycle_last
= 0;
299 clock
->cycle_last
= clocksource_read(clock
);
301 timekeeping_suspended
= 0;
302 write_sequnlock_irqrestore(&xtime_lock
, flags
);
304 touch_softlockup_watchdog();
306 clockevents_notify(CLOCK_EVT_NOTIFY_RESUME
, NULL
);
308 /* Resume hrtimers */
309 hres_timers_resume();
314 static int timekeeping_suspend(struct sys_device
*dev
, pm_message_t state
)
318 timekeeping_suspend_time
= read_persistent_clock();
320 write_seqlock_irqsave(&xtime_lock
, flags
);
321 clocksource_forward_now();
322 timekeeping_suspended
= 1;
323 write_sequnlock_irqrestore(&xtime_lock
, flags
);
325 clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND
, NULL
);
330 /* sysfs resume/suspend bits for timekeeping */
331 static struct sysdev_class timekeeping_sysclass
= {
332 .name
= "timekeeping",
333 .resume
= timekeeping_resume
,
334 .suspend
= timekeeping_suspend
,
337 static struct sys_device device_timer
= {
339 .cls
= &timekeeping_sysclass
,
342 static int __init
timekeeping_init_device(void)
344 int error
= sysdev_class_register(&timekeeping_sysclass
);
346 error
= sysdev_register(&device_timer
);
350 device_initcall(timekeeping_init_device
);
353 * If the error is already larger, we look ahead even further
354 * to compensate for late or lost adjustments.
356 static __always_inline
int clocksource_bigadjust(s64 error
, s64
*interval
,
364 * Use the current error value to determine how much to look ahead.
365 * The larger the error the slower we adjust for it to avoid problems
366 * with losing too many ticks, otherwise we would overadjust and
367 * produce an even larger error. The smaller the adjustment the
368 * faster we try to adjust for it, as lost ticks can do less harm
369 * here. This is tuned so that an error of about 1 msec is adjusted
370 * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
372 error2
= clock
->error
>> (NTP_SCALE_SHIFT
+ 22 - 2 * SHIFT_HZ
);
373 error2
= abs(error2
);
374 for (look_ahead
= 0; error2
> 0; look_ahead
++)
378 * Now calculate the error in (1 << look_ahead) ticks, but first
379 * remove the single look ahead already included in the error.
381 tick_error
= tick_length
>> (NTP_SCALE_SHIFT
- clock
->shift
+ 1);
382 tick_error
-= clock
->xtime_interval
>> 1;
383 error
= ((error
- tick_error
) >> look_ahead
) + tick_error
;
385 /* Finally calculate the adjustment shift value. */
390 *interval
= -*interval
;
394 for (adj
= 0; error
> i
; adj
++)
403 * Adjust the multiplier to reduce the error value,
404 * this is optimized for the most common adjustments of -1,0,1,
405 * for other values we can do a bit more work.
407 static void clocksource_adjust(s64 offset
)
409 s64 error
, interval
= clock
->cycle_interval
;
412 error
= clock
->error
>> (NTP_SCALE_SHIFT
- clock
->shift
- 1);
413 if (error
> interval
) {
415 if (likely(error
<= interval
))
418 adj
= clocksource_bigadjust(error
, &interval
, &offset
);
419 } else if (error
< -interval
) {
421 if (likely(error
>= -interval
)) {
423 interval
= -interval
;
426 adj
= clocksource_bigadjust(error
, &interval
, &offset
);
431 clock
->xtime_interval
+= interval
;
432 clock
->xtime_nsec
-= offset
;
433 clock
->error
-= (interval
- offset
) <<
434 (NTP_SCALE_SHIFT
- clock
->shift
);
438 * update_wall_time - Uses the current clocksource to increment the wall time
440 * Called from the timer interrupt, must hold a write on xtime_lock.
442 void update_wall_time(void)
446 /* Make sure we're fully resumed: */
447 if (unlikely(timekeeping_suspended
))
450 #ifdef CONFIG_GENERIC_TIME
451 offset
= (clocksource_read(clock
) - clock
->cycle_last
) & clock
->mask
;
453 offset
= clock
->cycle_interval
;
455 clock
->xtime_nsec
+= (s64
)xtime
.tv_nsec
<< clock
->shift
;
457 /* normally this loop will run just once, however in the
458 * case of lost or late ticks, it will accumulate correctly.
460 while (offset
>= clock
->cycle_interval
) {
461 /* accumulate one interval */
462 offset
-= clock
->cycle_interval
;
463 clock
->cycle_last
+= clock
->cycle_interval
;
465 clock
->xtime_nsec
+= clock
->xtime_interval
;
466 if (clock
->xtime_nsec
>= (u64
)NSEC_PER_SEC
<< clock
->shift
) {
467 clock
->xtime_nsec
-= (u64
)NSEC_PER_SEC
<< clock
->shift
;
472 /* accumulate error between NTP and clock interval */
473 clock
->error
+= tick_length
;
474 clock
->error
-= clock
->xtime_interval
<< (NTP_SCALE_SHIFT
- clock
->shift
);
477 /* correct the clock when NTP error is too big */
478 clocksource_adjust(offset
);
481 * Since in the loop above, we accumulate any amount of time
482 * in xtime_nsec over a second into xtime.tv_sec, its possible for
483 * xtime_nsec to be fairly small after the loop. Further, if we're
484 * slightly speeding the clocksource up in clocksource_adjust(),
485 * its possible the required corrective factor to xtime_nsec could
486 * cause it to underflow.
488 * Now, we cannot simply roll the accumulated second back, since
489 * the NTP subsystem has been notified via second_overflow. So
490 * instead we push xtime_nsec forward by the amount we underflowed,
491 * and add that amount into the error.
493 * We'll correct this error next time through this function, when
494 * xtime_nsec is not as small.
496 if (unlikely((s64
)clock
->xtime_nsec
< 0)) {
497 s64 neg
= -(s64
)clock
->xtime_nsec
;
498 clock
->xtime_nsec
= 0;
499 clock
->error
+= neg
<< (NTP_SCALE_SHIFT
- clock
->shift
);
502 /* store full nanoseconds into xtime */
503 xtime
.tv_nsec
= (s64
)clock
->xtime_nsec
>> clock
->shift
;
504 clock
->xtime_nsec
-= (s64
)xtime
.tv_nsec
<< clock
->shift
;
506 update_xtime_cache(cyc2ns(clock
, offset
));
508 /* check to see if there is a new clocksource to use */
509 change_clocksource();
510 update_vsyscall(&xtime
, clock
);
514 * getboottime - Return the real time of system boot.
515 * @ts: pointer to the timespec to be set
517 * Returns the time of day in a timespec.
519 * This is based on the wall_to_monotonic offset and the total suspend
520 * time. Calls to settimeofday will affect the value returned (which
521 * basically means that however wrong your real time clock is at boot time,
522 * you get the right time here).
524 void getboottime(struct timespec
*ts
)
526 set_normalized_timespec(ts
,
527 - (wall_to_monotonic
.tv_sec
+ total_sleep_time
),
528 - wall_to_monotonic
.tv_nsec
);
532 * monotonic_to_bootbased - Convert the monotonic time to boot based.
533 * @ts: pointer to the timespec to be converted
535 void monotonic_to_bootbased(struct timespec
*ts
)
537 ts
->tv_sec
+= total_sleep_time
;
540 unsigned long get_seconds(void)
542 return xtime_cache
.tv_sec
;
544 EXPORT_SYMBOL(get_seconds
);
547 struct timespec
current_kernel_time(void)
553 seq
= read_seqbegin(&xtime_lock
);
556 } while (read_seqretry(&xtime_lock
, seq
));
560 EXPORT_SYMBOL(current_kernel_time
);