aboutsummaryrefslogtreecommitdiff
path: root/kernel/time/timekeeping.c
blob: f682091fa8903fa94c2f8c93516925496b3a8db9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
/*
 *  linux/kernel/time/timekeeping.c
 *
 *  Kernel timekeeping code and accessor functions
 *
 *  This code was moved from linux/kernel/timer.c.
 *  Please see that file for copyright and history logs.
 *
 */

#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sysdev.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>


/*
 * This read-write spinlock protects us from races in SMP while
 * playing with xtime and avenrun.
 */
__attribute__((weak)) __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);

EXPORT_SYMBOL(xtime_lock);


/*
 * The current time
 * wall_to_monotonic is what we need to add to xtime (or xtime corrected
 * for sub jiffie times) to get to monotonic time.  Monotonic is pegged
 * at zero at system boot time, so wall_to_monotonic will be negative,
 * however, we will ALWAYS keep the tv_nsec part positive so we can use
 * the usual normalization.
 *
 * wall_to_monotonic is moved after resume from suspend for the monotonic
 * time not to jump. We need to add total_sleep_time to wall_to_monotonic
 * to get the real boot based time offset.
 *
 * - wall_to_monotonic is no longer the boot time, getboottime must be
 * used instead.
 */
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
static unsigned long total_sleep_time;		/* seconds */
EXPORT_SYMBOL(xtime);


#ifdef CONFIG_NO_HZ
static struct timespec xtime_cache __attribute__ ((aligned (16)));
static inline void update_xtime_cache(u64 nsec)
{
	xtime_cache = xtime;
	timespec_add_ns(&xtime_cache, nsec);
}
#else
#define xtime_cache xtime
/* We do *not* want to evaluate the argument for this case */
#define update_xtime_cache(n) do { } while (0)
#endif

static struct clocksource *clock; /* pointer to current clocksource */


#ifdef CONFIG_GENERIC_TIME
/**
 * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
 *
 * private function, must hold xtime_lock lock when being
 * called. Returns the number of nanoseconds since the
 * last call to update_wall_time() (adjusted by NTP scaling)
 */
static inline s64 __get_nsec_offset(void)
{
	cycle_t cycle_now, cycle_delta;
	s64 ns_offset;

	/* read clocksource: */
	cycle_now = clocksource_read(clock);

	/* calculate the delta since the last update_wall_time: */
	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;

	/* convert to nanoseconds: */
	ns_offset = cyc2ns(clock, cycle_delta);

	return ns_offset;
}

/**
 * __get_realtime_clock_ts - Returns the time of day in a timespec
 * @ts:		pointer to the timespec to be set
 *
 * Returns the time of day in a timespec. Used by
 * do_gettimeofday() and get_realtime_clock_ts().
 */
static inline void __get_realtime_clock_ts(struct timespec *ts)
{
	unsigned long seq;
	s64 nsecs;

	do {
		seq = read_seqbegin(&xtime_lock);

		*ts = xtime;
		nsecs = __get_nsec_offset();

	} while (read_seqretry(&xtime_lock, seq));

	timespec_add_ns(ts, nsecs);
}

/**
 * getnstimeofday - Returns the time of day in a timespec
 * @ts:		pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 */
void getnstimeofday(struct timespec *ts)
{
	__get_realtime_clock_ts(ts);
}

EXPORT_SYMBOL(getnstimeofday);

/**
 * do_gettimeofday - Returns the time of day in a timeval
 * @tv:		pointer to the timeval to be set
 *
 * NOTE: Users should be converted to using get_realtime_clock_ts()
 */
void do_gettimeofday(struct timeval *tv)
{
	struct timespec now;

	__get_realtime_clock_ts(&now);
	tv->tv_sec = now.tv_sec;
	tv->tv_usec = now.tv_nsec/1000;
}

EXPORT_SYMBOL(do_gettimeofday);
/**
 * do_settimeofday - Sets the time of day
 * @tv:		pointer to the timespec variable containing the new time
 *
 * Sets the time of day to the new time and update NTP and notify hrtimers
 */
int do_settimeofday(struct timespec *tv)
{
	unsigned long flags;
	time_t wtm_sec, sec = tv->tv_sec;
	long wtm_nsec, nsec = tv->tv_nsec;

	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
		return -EINVAL;

	write_seqlock_irqsave(&xtime_lock, flags);

	nsec -= __get_nsec_offset();

	wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
	wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);

	set_normalized_timespec(&xtime, sec, nsec);
	set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);

	clock->error = 0;
	ntp_clear();

	update_vsyscall(&xtime, clock);

	write_sequnlock_irqrestore(&xtime_lock, flags);

	/* signal hrtimers about time change */
	clock_was_set();

	return 0;
}

EXPORT_SYMBOL(do_settimeofday);

/**
 * change_clocksource - Swaps clocksources if a new one is available
 *
 * Accumulates current time interval and initializes new clocksource
 */
static void change_clocksource(void)
{
	struct clocksource *new;
	cycle_t now;
	u64 nsec;

	new = clocksource_get_next();

	if (clock == new)
		return;

	now = clocksource_read(new);
	nsec =  __get_nsec_offset();
	timespec_add_ns(&xtime, nsec);

	clock = new;
	clock->cycle_last = now;

	clock->error = 0;
	clock->xtime_nsec = 0;
	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);

	tick_clock_notify();

	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
	       clock->name);
}
#else
static inline void change_clocksource(void) { }
#endif

/**
 * timekeeping_is_continuous - check to see if timekeeping is free running
 */
int timekeeping_is_continuous(void)
{
	unsigned long seq;
	int ret;

	do {
		seq = read_seqbegin(&xtime_lock);

		ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;

	} while (read_seqretry(&xtime_lock, seq));

	return ret;
}

/**
 * read_persistent_clock -  Return time in seconds from the persistent clock.
 *
 * Weak dummy function for arches that do not yet support it.
 * Returns seconds from epoch using the battery backed persistent clock.
 * Returns zero if unsupported.
 *
 *  XXX - Do be sure to remove it once all arches implement it.
 */
unsigned long __attribute__((weak)) read_persistent_clock(void)
{
	return 0;
}

/*
 * timekeeping_init - Initializes the clocksource and common timekeeping values
 */
void __init timekeeping_init(void)
{
	unsigned long flags;
	unsigned long sec = read_persistent_clock();

	write_seqlock_irqsave(&xtime_lock, flags);

	ntp_clear();

	clock = clocksource_get_next();
	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
	clock->cycle_last = clocksource_read(clock);

	xtime.tv_sec = sec;
	xtime.tv_nsec = 0;
	set_normalized_timespec(&wall_to_monotonic,
		-xtime.tv_sec, -xtime.tv_nsec);
	total_sleep_time = 0;

	write_sequnlock_irqrestore(&xtime_lock, flags);
}

/* flag for if timekeeping is suspended */
static int timekeeping_suspended;
/* time in seconds when suspend began */
static unsigned long timekeeping_suspend_time;

/**
 * timekeeping_resume - Resumes the generic timekeeping subsystem.
 * @dev:	unused
 *
 * This is for the generic clocksource timekeeping.
 * xtime/wall_to_monotonic/jiffies/etc are
 * still managed by arch specific suspend/resume code.
 */
static int timekeeping_resume(struct sys_device *dev)
{
	unsigned long flags;
	unsigned long now = read_persistent_clock();

	clocksource_resume();

	write_seqlock_irqsave(&xtime_lock, flags);

	if (now && (now > timekeeping_suspend_time)) {
		unsigned long sleep_length = now - timekeeping_suspend_time;

		xtime.tv_sec += sleep_length;
		wall_to_monotonic.tv_sec -= sleep_length;
		total_sleep_time += sleep_length;
	}
	/* re-base the last cycle value */
	clock->cycle_last = clocksource_read(clock);
	clock->error = 0;
	timekeeping_suspended = 0;
	write_sequnlock_irqrestore(&xtime_lock, flags);

	touch_softlockup_watchdog();

	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);

	/* Resume hrtimers */
	hres_timers_resume();

	return 0;
}

static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
{
	unsigned long flags;

	timekeeping_suspend_time = read_persistent_clock();

	write_seqlock_irqsave(&xtime_lock, flags);
	timekeeping_suspended = 1;
	write_sequnlock_irqrestore(&xtime_lock, flags);

	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);

	return 0;
}

/* sysfs resume/suspend bits for timekeeping */
static struct sysdev_class timekeeping_sysclass = {
	.resume		= timekeeping_resume,
	.suspend	= timekeeping_suspend,
	set_kset_name("timekeeping"),
};

static struct sys_device device_timer = {
	.id		= 0,
	.cls		= &timekeeping_sysclass,
};

static int __init timekeeping_init_device(void)
{
	int error = sysdev_class_register(&timekeeping_sysclass);
	if (!error)
		error = sysdev_register(&device_timer);
	return error;
}

device_initcall(timekeeping_init_device);

/*
 * If the error is already larger, we look ahead even further
 * to compensate for late or lost adjustments.
 */
static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
						 s64 *offset)
{
	s64 tick_error, i;
	u32 look_ahead, adj;
	s32 error2, mult;

	/*
	 * Use the current error value to determine how much to look ahead.
	 * The larger the error the slower we adjust for it to avoid problems
	 * with losing too many ticks, otherwise we would overadjust and
	 * produce an even larger error.  The smaller the adjustment the
	 * faster we try to adjust for it, as lost ticks can do less harm
	 * here.  This is tuned so that an error of about 1 msec is adusted
	 * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
	 */
	error2 = clock->error >> (TICK_LENGTH_SHIFT + 22 - 2 * SHIFT_HZ);
	error2 = abs(error2);
	for (look_ahead = 0; error2 > 0; look_ahead++)
		error2 >>= 2;

	/*
	 * Now calculate the error in (1 << look_ahead) ticks, but first
	 * remove the single look ahead already included in the error.
	 */
	tick_error = current_tick_length() >>
		(TICK_LENGTH_SHIFT - clock->shift + 1);
	tick_error -= clock->xtime_interval >> 1;
	error = ((error - tick_error) >> look_ahead) + tick_error;

	/* Finally calculate the adjustment shift value.  */
	i = *interval;
	mult = 1;
	if (error < 0) {
		error = -error;
		*interval = -*interval;
		*offset = -*offset;
		mult = -1;
	}
	for (adj = 0; error > i; adj++)
		error >>= 1;

	*interval <<= adj;
	*offset <<= adj;
	return mult << adj;
}

/*
 * Adjust the multiplier to reduce the error value,
 * this is optimized for the most common adjustments of -1,0,1,
 * for other values we can do a bit more work.
 */
static void clocksource_adjust(s64 offset)
{
	s64 error, interval = clock->cycle_interval;
	int adj;

	error = clock->error >> (TICK_LENGTH_SHIFT - clock->shift - 1);
	if (error > interval) {
		error >>= 2;
		if (likely(error <= interval))
			adj = 1;
		else
			adj = clocksource_bigadjust(error, &interval, &offset);
	} else if (error < -interval) {
		error >>= 2;
		if (likely(error >= -interval)) {
			adj = -1;
			interval = -interval;
			offset = -offset;
		} else
			adj = clocksource_bigadjust(error, &interval, &offset);
	} else
		return;

	clock->mult += adj;
	clock->xtime_interval += interval;
	clock->xtime_nsec -= offset;
	clock->error -= (interval - offset) <<
			(TICK_LENGTH_SHIFT - clock->shift);
}

/**
 * update_wall_time - Uses the current clocksource to increment the wall time
 *
 * Called from the timer interrupt, must hold a write on xtime_lock.
 */
void update_wall_time(void)
{
	cycle_t offset;

	/* Make sure we're fully resumed: */
	if (unlikely(timekeeping_suspended))
		return;

#ifdef CONFIG_GENERIC_TIME
	offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
#else
	offset = clock->cycle_interval;
#endif
	clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;

	/* normally this loop will run just once, however in the
	 * case of lost or late ticks, it will accumulate correctly.
	 */
	while (offset >= clock->cycle_interval) {
		/* accumulate one interval */
		clock->xtime_nsec += clock->xtime_interval;
		clock->cycle_last += clock->cycle_interval;
		offset -= clock->cycle_interval;

		if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
			clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
			xtime.tv_sec++;
			second_overflow();
		}

		/* accumulate error between NTP and clock interval */
		clock->error += current_tick_length();
		clock->error -= clock->xtime_interval << (TICK_LENGTH_SHIFT - clock->shift);
	}

	/* correct the clock when NTP error is too big */
	clocksource_adjust(offset);

	/* store full nanoseconds into xtime */
	xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;

	update_xtime_cache(cyc2ns(clock, offset));

	/* check to see if there is a new clocksource to use */
	change_clocksource();
	update_vsyscall(&xtime, clock);
}

/**
 * getboottime - Return the real time of system boot.
 * @ts:		pointer to the timespec to be set
 *
 * Returns the time of day in a timespec.
 *
 * This is based on the wall_to_monotonic offset and the total suspend
 * time. Calls to settimeofday will affect the value returned (which
 * basically means that however wrong your real time clock is at boot time,
 * you get the right time here).
 */
void getboottime(struct timespec *ts)
{
	set_normalized_timespec(ts,
		- (wall_to_monotonic.tv_sec + total_sleep_time),
		- wall_to_monotonic.tv_nsec);
}

/**
 * monotonic_to_bootbased - Convert the monotonic time to boot based.
 * @ts:		pointer to the timespec to be converted
 */
void monotonic_to_bootbased(struct timespec *ts)
{
	ts->tv_sec += total_sleep_time;
}

unsigned long get_seconds(void)
{
	return xtime_cache.tv_sec;
}
EXPORT_SYMBOL(get_seconds);


struct timespec current_kernel_time(void)
{
	struct timespec now;
	unsigned long seq;

	do {
		seq = read_seqbegin(&xtime_lock);

		now = xtime_cache;
	} while (read_seqretry(&xtime_lock, seq));

	return now;
}
EXPORT_SYMBOL(current_kernel_time);