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 __attribute__((weak
)) __cacheline_aligned_in_smp
DEFINE_SEQLOCK(xtime_lock
);
29 EXPORT_SYMBOL(xtime_lock
);
34 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
35 * for sub jiffie times) to get to monotonic time. Monotonic is pegged
36 * at zero at system boot time, so wall_to_monotonic will be negative,
37 * however, we will ALWAYS keep the tv_nsec part positive so we can use
38 * the usual normalization.
40 * wall_to_monotonic is moved after resume from suspend for the monotonic
41 * time not to jump. We need to add total_sleep_time to wall_to_monotonic
42 * to get the real boot based time offset.
44 * - wall_to_monotonic is no longer the boot time, getboottime must be
47 struct timespec xtime
__attribute__ ((aligned (16)));
48 struct timespec wall_to_monotonic
__attribute__ ((aligned (16)));
49 static unsigned long total_sleep_time
; /* seconds */
54 static struct timespec xtime_cache
__attribute__ ((aligned (16)));
55 static inline void update_xtime_cache(u64 nsec
)
58 timespec_add_ns(&xtime_cache
, nsec
);
61 #define xtime_cache xtime
62 /* We do *not* want to evaluate the argument for this case */
63 #define update_xtime_cache(n) do { } while (0)
66 static struct clocksource
*clock
; /* pointer to current clocksource */
69 #ifdef CONFIG_GENERIC_TIME
71 * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
73 * private function, must hold xtime_lock lock when being
74 * called. Returns the number of nanoseconds since the
75 * last call to update_wall_time() (adjusted by NTP scaling)
77 static inline s64
__get_nsec_offset(void)
79 cycle_t cycle_now
, cycle_delta
;
82 /* read clocksource: */
83 cycle_now
= clocksource_read(clock
);
85 /* calculate the delta since the last update_wall_time: */
86 cycle_delta
= (cycle_now
- clock
->cycle_last
) & clock
->mask
;
88 /* convert to nanoseconds: */
89 ns_offset
= cyc2ns(clock
, cycle_delta
);
95 * __get_realtime_clock_ts - Returns the time of day in a timespec
96 * @ts: pointer to the timespec to be set
98 * Returns the time of day in a timespec. Used by
99 * do_gettimeofday() and get_realtime_clock_ts().
101 static inline void __get_realtime_clock_ts(struct timespec
*ts
)
107 seq
= read_seqbegin(&xtime_lock
);
110 nsecs
= __get_nsec_offset();
112 } while (read_seqretry(&xtime_lock
, seq
));
114 timespec_add_ns(ts
, nsecs
);
118 * getnstimeofday - Returns the time of day in a timespec
119 * @ts: pointer to the timespec to be set
121 * Returns the time of day in a timespec.
123 void getnstimeofday(struct timespec
*ts
)
125 __get_realtime_clock_ts(ts
);
128 EXPORT_SYMBOL(getnstimeofday
);
131 * do_gettimeofday - Returns the time of day in a timeval
132 * @tv: pointer to the timeval to be set
134 * NOTE: Users should be converted to using get_realtime_clock_ts()
136 void do_gettimeofday(struct timeval
*tv
)
140 __get_realtime_clock_ts(&now
);
141 tv
->tv_sec
= now
.tv_sec
;
142 tv
->tv_usec
= now
.tv_nsec
/1000;
145 EXPORT_SYMBOL(do_gettimeofday
);
147 * do_settimeofday - Sets the time of day
148 * @tv: pointer to the timespec variable containing the new time
150 * Sets the time of day to the new time and update NTP and notify hrtimers
152 int do_settimeofday(struct timespec
*tv
)
155 time_t wtm_sec
, sec
= tv
->tv_sec
;
156 long wtm_nsec
, nsec
= tv
->tv_nsec
;
158 if ((unsigned long)tv
->tv_nsec
>= NSEC_PER_SEC
)
161 write_seqlock_irqsave(&xtime_lock
, flags
);
163 nsec
-= __get_nsec_offset();
165 wtm_sec
= wall_to_monotonic
.tv_sec
+ (xtime
.tv_sec
- sec
);
166 wtm_nsec
= wall_to_monotonic
.tv_nsec
+ (xtime
.tv_nsec
- nsec
);
168 set_normalized_timespec(&xtime
, sec
, nsec
);
169 set_normalized_timespec(&wall_to_monotonic
, wtm_sec
, wtm_nsec
);
174 update_vsyscall(&xtime
, clock
);
176 write_sequnlock_irqrestore(&xtime_lock
, flags
);
178 /* signal hrtimers about time change */
184 EXPORT_SYMBOL(do_settimeofday
);
187 * change_clocksource - Swaps clocksources if a new one is available
189 * Accumulates current time interval and initializes new clocksource
191 static void change_clocksource(void)
193 struct clocksource
*new;
197 new = clocksource_get_next();
202 now
= clocksource_read(new);
203 nsec
= __get_nsec_offset();
204 timespec_add_ns(&xtime
, nsec
);
207 clock
->cycle_last
= now
;
210 clock
->xtime_nsec
= 0;
211 clocksource_calculate_interval(clock
, NTP_INTERVAL_LENGTH
);
215 printk(KERN_INFO
"Time: %s clocksource has been installed.\n",
219 static inline void change_clocksource(void) { }
223 * timekeeping_is_continuous - check to see if timekeeping is free running
225 int timekeeping_is_continuous(void)
231 seq
= read_seqbegin(&xtime_lock
);
233 ret
= clock
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
;
235 } while (read_seqretry(&xtime_lock
, seq
));
241 * read_persistent_clock - Return time in seconds from the persistent clock.
243 * Weak dummy function for arches that do not yet support it.
244 * Returns seconds from epoch using the battery backed persistent clock.
245 * Returns zero if unsupported.
247 * XXX - Do be sure to remove it once all arches implement it.
249 unsigned long __attribute__((weak
)) read_persistent_clock(void)
255 * timekeeping_init - Initializes the clocksource and common timekeeping values
257 void __init
timekeeping_init(void)
260 unsigned long sec
= read_persistent_clock();
262 write_seqlock_irqsave(&xtime_lock
, flags
);
266 clock
= clocksource_get_next();
267 clocksource_calculate_interval(clock
, NTP_INTERVAL_LENGTH
);
268 clock
->cycle_last
= clocksource_read(clock
);
272 set_normalized_timespec(&wall_to_monotonic
,
273 -xtime
.tv_sec
, -xtime
.tv_nsec
);
274 total_sleep_time
= 0;
276 write_sequnlock_irqrestore(&xtime_lock
, flags
);
279 /* flag for if timekeeping is suspended */
280 static int timekeeping_suspended
;
281 /* time in seconds when suspend began */
282 static unsigned long timekeeping_suspend_time
;
285 * timekeeping_resume - Resumes the generic timekeeping subsystem.
288 * This is for the generic clocksource timekeeping.
289 * xtime/wall_to_monotonic/jiffies/etc are
290 * still managed by arch specific suspend/resume code.
292 static int timekeeping_resume(struct sys_device
*dev
)
295 unsigned long now
= read_persistent_clock();
297 clocksource_resume();
299 write_seqlock_irqsave(&xtime_lock
, flags
);
301 if (now
&& (now
> timekeeping_suspend_time
)) {
302 unsigned long sleep_length
= now
- timekeeping_suspend_time
;
304 xtime
.tv_sec
+= sleep_length
;
305 wall_to_monotonic
.tv_sec
-= sleep_length
;
306 total_sleep_time
+= sleep_length
;
308 /* re-base the last cycle value */
309 clock
->cycle_last
= clocksource_read(clock
);
311 timekeeping_suspended
= 0;
312 write_sequnlock_irqrestore(&xtime_lock
, flags
);
314 touch_softlockup_watchdog();
316 clockevents_notify(CLOCK_EVT_NOTIFY_RESUME
, NULL
);
318 /* Resume hrtimers */
319 hres_timers_resume();
324 static int timekeeping_suspend(struct sys_device
*dev
, pm_message_t state
)
328 write_seqlock_irqsave(&xtime_lock
, flags
);
329 timekeeping_suspended
= 1;
330 timekeeping_suspend_time
= read_persistent_clock();
331 write_sequnlock_irqrestore(&xtime_lock
, flags
);
333 clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND
, NULL
);
338 /* sysfs resume/suspend bits for timekeeping */
339 static struct sysdev_class timekeeping_sysclass
= {
340 .resume
= timekeeping_resume
,
341 .suspend
= timekeeping_suspend
,
342 set_kset_name("timekeeping"),
345 static struct sys_device device_timer
= {
347 .cls
= &timekeeping_sysclass
,
350 static int __init
timekeeping_init_device(void)
352 int error
= sysdev_class_register(&timekeeping_sysclass
);
354 error
= sysdev_register(&device_timer
);
358 device_initcall(timekeeping_init_device
);
361 * If the error is already larger, we look ahead even further
362 * to compensate for late or lost adjustments.
364 static __always_inline
int clocksource_bigadjust(s64 error
, s64
*interval
,
372 * Use the current error value to determine how much to look ahead.
373 * The larger the error the slower we adjust for it to avoid problems
374 * with losing too many ticks, otherwise we would overadjust and
375 * produce an even larger error. The smaller the adjustment the
376 * faster we try to adjust for it, as lost ticks can do less harm
377 * here. This is tuned so that an error of about 1 msec is adusted
378 * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
380 error2
= clock
->error
>> (TICK_LENGTH_SHIFT
+ 22 - 2 * SHIFT_HZ
);
381 error2
= abs(error2
);
382 for (look_ahead
= 0; error2
> 0; look_ahead
++)
386 * Now calculate the error in (1 << look_ahead) ticks, but first
387 * remove the single look ahead already included in the error.
389 tick_error
= current_tick_length() >>
390 (TICK_LENGTH_SHIFT
- clock
->shift
+ 1);
391 tick_error
-= clock
->xtime_interval
>> 1;
392 error
= ((error
- tick_error
) >> look_ahead
) + tick_error
;
394 /* Finally calculate the adjustment shift value. */
399 *interval
= -*interval
;
403 for (adj
= 0; error
> i
; adj
++)
412 * Adjust the multiplier to reduce the error value,
413 * this is optimized for the most common adjustments of -1,0,1,
414 * for other values we can do a bit more work.
416 static void clocksource_adjust(s64 offset
)
418 s64 error
, interval
= clock
->cycle_interval
;
421 error
= clock
->error
>> (TICK_LENGTH_SHIFT
- clock
->shift
- 1);
422 if (error
> interval
) {
424 if (likely(error
<= interval
))
427 adj
= clocksource_bigadjust(error
, &interval
, &offset
);
428 } else if (error
< -interval
) {
430 if (likely(error
>= -interval
)) {
432 interval
= -interval
;
435 adj
= clocksource_bigadjust(error
, &interval
, &offset
);
440 clock
->xtime_interval
+= interval
;
441 clock
->xtime_nsec
-= offset
;
442 clock
->error
-= (interval
- offset
) <<
443 (TICK_LENGTH_SHIFT
- clock
->shift
);
447 * update_wall_time - Uses the current clocksource to increment the wall time
449 * Called from the timer interrupt, must hold a write on xtime_lock.
451 void update_wall_time(void)
455 /* Make sure we're fully resumed: */
456 if (unlikely(timekeeping_suspended
))
459 #ifdef CONFIG_GENERIC_TIME
460 offset
= (clocksource_read(clock
) - clock
->cycle_last
) & clock
->mask
;
462 offset
= clock
->cycle_interval
;
464 clock
->xtime_nsec
+= (s64
)xtime
.tv_nsec
<< clock
->shift
;
466 /* normally this loop will run just once, however in the
467 * case of lost or late ticks, it will accumulate correctly.
469 while (offset
>= clock
->cycle_interval
) {
470 /* accumulate one interval */
471 clock
->xtime_nsec
+= clock
->xtime_interval
;
472 clock
->cycle_last
+= clock
->cycle_interval
;
473 offset
-= clock
->cycle_interval
;
475 if (clock
->xtime_nsec
>= (u64
)NSEC_PER_SEC
<< clock
->shift
) {
476 clock
->xtime_nsec
-= (u64
)NSEC_PER_SEC
<< clock
->shift
;
481 /* accumulate error between NTP and clock interval */
482 clock
->error
+= current_tick_length();
483 clock
->error
-= clock
->xtime_interval
<< (TICK_LENGTH_SHIFT
- clock
->shift
);
486 /* correct the clock when NTP error is too big */
487 clocksource_adjust(offset
);
489 /* store full nanoseconds into xtime */
490 xtime
.tv_nsec
= (s64
)clock
->xtime_nsec
>> clock
->shift
;
491 clock
->xtime_nsec
-= (s64
)xtime
.tv_nsec
<< clock
->shift
;
493 update_xtime_cache(cyc2ns(clock
, offset
));
495 /* check to see if there is a new clocksource to use */
496 change_clocksource();
497 update_vsyscall(&xtime
, clock
);
501 * getboottime - Return the real time of system boot.
502 * @ts: pointer to the timespec to be set
504 * Returns the time of day in a timespec.
506 * This is based on the wall_to_monotonic offset and the total suspend
507 * time. Calls to settimeofday will affect the value returned (which
508 * basically means that however wrong your real time clock is at boot time,
509 * you get the right time here).
511 void getboottime(struct timespec
*ts
)
513 set_normalized_timespec(ts
,
514 - (wall_to_monotonic
.tv_sec
+ total_sleep_time
),
515 - wall_to_monotonic
.tv_nsec
);
519 * monotonic_to_bootbased - Convert the monotonic time to boot based.
520 * @ts: pointer to the timespec to be converted
522 void monotonic_to_bootbased(struct timespec
*ts
)
524 ts
->tv_sec
+= total_sleep_time
;
527 unsigned long get_seconds(void)
529 return xtime_cache
.tv_sec
;
531 EXPORT_SYMBOL(get_seconds
);
534 struct timespec
current_kernel_time(void)
540 seq
= read_seqbegin(&xtime_lock
);
543 } while (read_seqretry(&xtime_lock
, seq
));
547 EXPORT_SYMBOL(current_kernel_time
);