8524070b |
1 | /* |
2 | * linux/kernel/time/timekeeping.c |
3 | * |
4 | * Kernel timekeeping code and accessor functions |
5 | * |
6 | * This code was moved from linux/kernel/timer.c. |
7 | * Please see that file for copyright and history logs. |
8 | * |
9 | */ |
10 | |
11 | #include <linux/module.h> |
12 | #include <linux/interrupt.h> |
13 | #include <linux/percpu.h> |
14 | #include <linux/init.h> |
15 | #include <linux/mm.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> |
21 | |
22 | |
23 | /* |
24 | * This read-write spinlock protects us from races in SMP while |
25 | * playing with xtime and avenrun. |
26 | */ |
27 | __attribute__((weak)) __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock); |
28 | |
29 | EXPORT_SYMBOL(xtime_lock); |
30 | |
31 | |
32 | /* |
33 | * The current time |
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. |
39 | */ |
40 | struct timespec xtime __attribute__ ((aligned (16))); |
41 | struct timespec wall_to_monotonic __attribute__ ((aligned (16))); |
42 | |
43 | EXPORT_SYMBOL(xtime); |
44 | |
45 | |
46 | static struct clocksource *clock; /* pointer to current clocksource */ |
47 | |
48 | |
49 | #ifdef CONFIG_GENERIC_TIME |
50 | /** |
51 | * __get_nsec_offset - Returns nanoseconds since last call to periodic_hook |
52 | * |
53 | * private function, must hold xtime_lock lock when being |
54 | * called. Returns the number of nanoseconds since the |
55 | * last call to update_wall_time() (adjusted by NTP scaling) |
56 | */ |
57 | static inline s64 __get_nsec_offset(void) |
58 | { |
59 | cycle_t cycle_now, cycle_delta; |
60 | s64 ns_offset; |
61 | |
62 | /* read clocksource: */ |
63 | cycle_now = clocksource_read(clock); |
64 | |
65 | /* calculate the delta since the last update_wall_time: */ |
66 | cycle_delta = (cycle_now - clock->cycle_last) & clock->mask; |
67 | |
68 | /* convert to nanoseconds: */ |
69 | ns_offset = cyc2ns(clock, cycle_delta); |
70 | |
71 | return ns_offset; |
72 | } |
73 | |
74 | /** |
75 | * __get_realtime_clock_ts - Returns the time of day in a timespec |
76 | * @ts: pointer to the timespec to be set |
77 | * |
78 | * Returns the time of day in a timespec. Used by |
79 | * do_gettimeofday() and get_realtime_clock_ts(). |
80 | */ |
81 | static inline void __get_realtime_clock_ts(struct timespec *ts) |
82 | { |
83 | unsigned long seq; |
84 | s64 nsecs; |
85 | |
86 | do { |
87 | seq = read_seqbegin(&xtime_lock); |
88 | |
89 | *ts = xtime; |
90 | nsecs = __get_nsec_offset(); |
91 | |
92 | } while (read_seqretry(&xtime_lock, seq)); |
93 | |
94 | timespec_add_ns(ts, nsecs); |
95 | } |
96 | |
97 | /** |
98 | * getnstimeofday - Returns the time of day in a timespec |
99 | * @ts: pointer to the timespec to be set |
100 | * |
101 | * Returns the time of day in a timespec. |
102 | */ |
103 | void getnstimeofday(struct timespec *ts) |
104 | { |
105 | __get_realtime_clock_ts(ts); |
106 | } |
107 | |
108 | EXPORT_SYMBOL(getnstimeofday); |
109 | |
110 | /** |
111 | * do_gettimeofday - Returns the time of day in a timeval |
112 | * @tv: pointer to the timeval to be set |
113 | * |
114 | * NOTE: Users should be converted to using get_realtime_clock_ts() |
115 | */ |
116 | void do_gettimeofday(struct timeval *tv) |
117 | { |
118 | struct timespec now; |
119 | |
120 | __get_realtime_clock_ts(&now); |
121 | tv->tv_sec = now.tv_sec; |
122 | tv->tv_usec = now.tv_nsec/1000; |
123 | } |
124 | |
125 | EXPORT_SYMBOL(do_gettimeofday); |
126 | /** |
127 | * do_settimeofday - Sets the time of day |
128 | * @tv: pointer to the timespec variable containing the new time |
129 | * |
130 | * Sets the time of day to the new time and update NTP and notify hrtimers |
131 | */ |
132 | int do_settimeofday(struct timespec *tv) |
133 | { |
134 | unsigned long flags; |
135 | time_t wtm_sec, sec = tv->tv_sec; |
136 | long wtm_nsec, nsec = tv->tv_nsec; |
137 | |
138 | if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC) |
139 | return -EINVAL; |
140 | |
141 | write_seqlock_irqsave(&xtime_lock, flags); |
142 | |
143 | nsec -= __get_nsec_offset(); |
144 | |
145 | wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec); |
146 | wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec); |
147 | |
148 | set_normalized_timespec(&xtime, sec, nsec); |
149 | set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec); |
150 | |
151 | clock->error = 0; |
152 | ntp_clear(); |
153 | |
154 | update_vsyscall(&xtime, clock); |
155 | |
156 | write_sequnlock_irqrestore(&xtime_lock, flags); |
157 | |
158 | /* signal hrtimers about time change */ |
159 | clock_was_set(); |
160 | |
161 | return 0; |
162 | } |
163 | |
164 | EXPORT_SYMBOL(do_settimeofday); |
165 | |
166 | /** |
167 | * change_clocksource - Swaps clocksources if a new one is available |
168 | * |
169 | * Accumulates current time interval and initializes new clocksource |
170 | */ |
171 | static void change_clocksource(void) |
172 | { |
173 | struct clocksource *new; |
174 | cycle_t now; |
175 | u64 nsec; |
176 | |
177 | new = clocksource_get_next(); |
178 | |
179 | if (clock == new) |
180 | return; |
181 | |
182 | now = clocksource_read(new); |
183 | nsec = __get_nsec_offset(); |
184 | timespec_add_ns(&xtime, nsec); |
185 | |
186 | clock = new; |
187 | clock->cycle_last = now; |
188 | |
189 | clock->error = 0; |
190 | clock->xtime_nsec = 0; |
191 | clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH); |
192 | |
193 | tick_clock_notify(); |
194 | |
195 | printk(KERN_INFO "Time: %s clocksource has been installed.\n", |
196 | clock->name); |
197 | } |
198 | #else |
199 | static inline void change_clocksource(void) { } |
200 | #endif |
201 | |
202 | /** |
203 | * timekeeping_is_continuous - check to see if timekeeping is free running |
204 | */ |
205 | int timekeeping_is_continuous(void) |
206 | { |
207 | unsigned long seq; |
208 | int ret; |
209 | |
210 | do { |
211 | seq = read_seqbegin(&xtime_lock); |
212 | |
213 | ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES; |
214 | |
215 | } while (read_seqretry(&xtime_lock, seq)); |
216 | |
217 | return ret; |
218 | } |
219 | |
220 | /** |
221 | * read_persistent_clock - Return time in seconds from the persistent clock. |
222 | * |
223 | * Weak dummy function for arches that do not yet support it. |
224 | * Returns seconds from epoch using the battery backed persistent clock. |
225 | * Returns zero if unsupported. |
226 | * |
227 | * XXX - Do be sure to remove it once all arches implement it. |
228 | */ |
229 | unsigned long __attribute__((weak)) read_persistent_clock(void) |
230 | { |
231 | return 0; |
232 | } |
233 | |
234 | /* |
235 | * timekeeping_init - Initializes the clocksource and common timekeeping values |
236 | */ |
237 | void __init timekeeping_init(void) |
238 | { |
239 | unsigned long flags; |
240 | unsigned long sec = read_persistent_clock(); |
241 | |
242 | write_seqlock_irqsave(&xtime_lock, flags); |
243 | |
244 | ntp_clear(); |
245 | |
246 | clock = clocksource_get_next(); |
247 | clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH); |
248 | clock->cycle_last = clocksource_read(clock); |
249 | |
250 | xtime.tv_sec = sec; |
251 | xtime.tv_nsec = 0; |
252 | set_normalized_timespec(&wall_to_monotonic, |
253 | -xtime.tv_sec, -xtime.tv_nsec); |
254 | |
255 | write_sequnlock_irqrestore(&xtime_lock, flags); |
256 | } |
257 | |
258 | /* flag for if timekeeping is suspended */ |
259 | static int timekeeping_suspended; |
260 | /* time in seconds when suspend began */ |
261 | static unsigned long timekeeping_suspend_time; |
262 | |
263 | /** |
264 | * timekeeping_resume - Resumes the generic timekeeping subsystem. |
265 | * @dev: unused |
266 | * |
267 | * This is for the generic clocksource timekeeping. |
268 | * xtime/wall_to_monotonic/jiffies/etc are |
269 | * still managed by arch specific suspend/resume code. |
270 | */ |
271 | static int timekeeping_resume(struct sys_device *dev) |
272 | { |
273 | unsigned long flags; |
274 | unsigned long now = read_persistent_clock(); |
275 | |
276 | write_seqlock_irqsave(&xtime_lock, flags); |
277 | |
278 | if (now && (now > timekeeping_suspend_time)) { |
279 | unsigned long sleep_length = now - timekeeping_suspend_time; |
280 | |
281 | xtime.tv_sec += sleep_length; |
282 | wall_to_monotonic.tv_sec -= sleep_length; |
283 | } |
284 | /* re-base the last cycle value */ |
285 | clock->cycle_last = clocksource_read(clock); |
286 | clock->error = 0; |
287 | timekeeping_suspended = 0; |
288 | write_sequnlock_irqrestore(&xtime_lock, flags); |
289 | |
290 | touch_softlockup_watchdog(); |
291 | |
292 | clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL); |
293 | |
294 | /* Resume hrtimers */ |
295 | hres_timers_resume(); |
296 | |
297 | return 0; |
298 | } |
299 | |
300 | static int timekeeping_suspend(struct sys_device *dev, pm_message_t state) |
301 | { |
302 | unsigned long flags; |
303 | |
304 | write_seqlock_irqsave(&xtime_lock, flags); |
305 | timekeeping_suspended = 1; |
306 | timekeeping_suspend_time = read_persistent_clock(); |
307 | write_sequnlock_irqrestore(&xtime_lock, flags); |
308 | |
309 | clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL); |
310 | |
311 | return 0; |
312 | } |
313 | |
314 | /* sysfs resume/suspend bits for timekeeping */ |
315 | static struct sysdev_class timekeeping_sysclass = { |
316 | .resume = timekeeping_resume, |
317 | .suspend = timekeeping_suspend, |
318 | set_kset_name("timekeeping"), |
319 | }; |
320 | |
321 | static struct sys_device device_timer = { |
322 | .id = 0, |
323 | .cls = &timekeeping_sysclass, |
324 | }; |
325 | |
326 | static int __init timekeeping_init_device(void) |
327 | { |
328 | int error = sysdev_class_register(&timekeeping_sysclass); |
329 | if (!error) |
330 | error = sysdev_register(&device_timer); |
331 | return error; |
332 | } |
333 | |
334 | device_initcall(timekeeping_init_device); |
335 | |
336 | /* |
337 | * If the error is already larger, we look ahead even further |
338 | * to compensate for late or lost adjustments. |
339 | */ |
340 | static __always_inline int clocksource_bigadjust(s64 error, s64 *interval, |
341 | s64 *offset) |
342 | { |
343 | s64 tick_error, i; |
344 | u32 look_ahead, adj; |
345 | s32 error2, mult; |
346 | |
347 | /* |
348 | * Use the current error value to determine how much to look ahead. |
349 | * The larger the error the slower we adjust for it to avoid problems |
350 | * with losing too many ticks, otherwise we would overadjust and |
351 | * produce an even larger error. The smaller the adjustment the |
352 | * faster we try to adjust for it, as lost ticks can do less harm |
353 | * here. This is tuned so that an error of about 1 msec is adusted |
354 | * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks). |
355 | */ |
356 | error2 = clock->error >> (TICK_LENGTH_SHIFT + 22 - 2 * SHIFT_HZ); |
357 | error2 = abs(error2); |
358 | for (look_ahead = 0; error2 > 0; look_ahead++) |
359 | error2 >>= 2; |
360 | |
361 | /* |
362 | * Now calculate the error in (1 << look_ahead) ticks, but first |
363 | * remove the single look ahead already included in the error. |
364 | */ |
365 | tick_error = current_tick_length() >> |
366 | (TICK_LENGTH_SHIFT - clock->shift + 1); |
367 | tick_error -= clock->xtime_interval >> 1; |
368 | error = ((error - tick_error) >> look_ahead) + tick_error; |
369 | |
370 | /* Finally calculate the adjustment shift value. */ |
371 | i = *interval; |
372 | mult = 1; |
373 | if (error < 0) { |
374 | error = -error; |
375 | *interval = -*interval; |
376 | *offset = -*offset; |
377 | mult = -1; |
378 | } |
379 | for (adj = 0; error > i; adj++) |
380 | error >>= 1; |
381 | |
382 | *interval <<= adj; |
383 | *offset <<= adj; |
384 | return mult << adj; |
385 | } |
386 | |
387 | /* |
388 | * Adjust the multiplier to reduce the error value, |
389 | * this is optimized for the most common adjustments of -1,0,1, |
390 | * for other values we can do a bit more work. |
391 | */ |
392 | static void clocksource_adjust(struct clocksource *clock, s64 offset) |
393 | { |
394 | s64 error, interval = clock->cycle_interval; |
395 | int adj; |
396 | |
397 | error = clock->error >> (TICK_LENGTH_SHIFT - clock->shift - 1); |
398 | if (error > interval) { |
399 | error >>= 2; |
400 | if (likely(error <= interval)) |
401 | adj = 1; |
402 | else |
403 | adj = clocksource_bigadjust(error, &interval, &offset); |
404 | } else if (error < -interval) { |
405 | error >>= 2; |
406 | if (likely(error >= -interval)) { |
407 | adj = -1; |
408 | interval = -interval; |
409 | offset = -offset; |
410 | } else |
411 | adj = clocksource_bigadjust(error, &interval, &offset); |
412 | } else |
413 | return; |
414 | |
415 | clock->mult += adj; |
416 | clock->xtime_interval += interval; |
417 | clock->xtime_nsec -= offset; |
418 | clock->error -= (interval - offset) << |
419 | (TICK_LENGTH_SHIFT - clock->shift); |
420 | } |
421 | |
422 | /** |
423 | * update_wall_time - Uses the current clocksource to increment the wall time |
424 | * |
425 | * Called from the timer interrupt, must hold a write on xtime_lock. |
426 | */ |
427 | void update_wall_time(void) |
428 | { |
429 | cycle_t offset; |
430 | |
431 | /* Make sure we're fully resumed: */ |
432 | if (unlikely(timekeeping_suspended)) |
433 | return; |
434 | |
435 | #ifdef CONFIG_GENERIC_TIME |
436 | offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask; |
437 | #else |
438 | offset = clock->cycle_interval; |
439 | #endif |
440 | clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift; |
441 | |
442 | /* normally this loop will run just once, however in the |
443 | * case of lost or late ticks, it will accumulate correctly. |
444 | */ |
445 | while (offset >= clock->cycle_interval) { |
446 | /* accumulate one interval */ |
447 | clock->xtime_nsec += clock->xtime_interval; |
448 | clock->cycle_last += clock->cycle_interval; |
449 | offset -= clock->cycle_interval; |
450 | |
451 | if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) { |
452 | clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift; |
453 | xtime.tv_sec++; |
454 | second_overflow(); |
455 | } |
456 | |
457 | /* interpolator bits */ |
458 | time_interpolator_update(clock->xtime_interval |
459 | >> clock->shift); |
460 | |
461 | /* accumulate error between NTP and clock interval */ |
462 | clock->error += current_tick_length(); |
463 | clock->error -= clock->xtime_interval << (TICK_LENGTH_SHIFT - clock->shift); |
464 | } |
465 | |
466 | /* correct the clock when NTP error is too big */ |
467 | clocksource_adjust(clock, offset); |
468 | |
469 | /* store full nanoseconds into xtime */ |
470 | xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift; |
471 | clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; |
472 | |
473 | /* check to see if there is a new clocksource to use */ |
474 | change_clocksource(); |
475 | update_vsyscall(&xtime, clock); |
476 | } |