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1/*
2 * sched_clock() for unstable CPU clocks
3 *
4 * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
5 *
6 * Updates and enhancements:
7 * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
8 *
9 * Based on code by:
10 * Ingo Molnar <mingo@redhat.com>
11 * Guillaume Chazarain <guichaz@gmail.com>
12 *
13 *
14 * What this file implements:
15 *
16 * cpu_clock(i) provides a fast (execution time) high resolution
17 * clock with bounded drift between CPUs. The value of cpu_clock(i)
18 * is monotonic for constant i. The timestamp returned is in nanoseconds.
19 *
20 * ######################### BIG FAT WARNING ##########################
21 * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
22 * # go backwards !! #
23 * ####################################################################
24 *
25 * There is no strict promise about the base, although it tends to start
26 * at 0 on boot (but people really shouldn't rely on that).
27 *
28 * cpu_clock(i) -- can be used from any context, including NMI.
29 * local_clock() -- is cpu_clock() on the current CPU.
30 *
31 * sched_clock_cpu(i)
32 *
33 * How it is implemented:
34 *
35 * The implementation either uses sched_clock() when
36 * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
37 * sched_clock() is assumed to provide these properties (mostly it means
38 * the architecture provides a globally synchronized highres time source).
39 *
40 * Otherwise it tries to create a semi stable clock from a mixture of other
41 * clocks, including:
42 *
43 * - GTOD (clock monotomic)
44 * - sched_clock()
45 * - explicit idle events
46 *
47 * We use GTOD as base and use sched_clock() deltas to improve resolution. The
48 * deltas are filtered to provide monotonicity and keeping it within an
49 * expected window.
50 *
51 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
52 * that is otherwise invisible (TSC gets stopped).
53 *
54 */
55#include "sched.h"
56
57/*
58 * Scheduler clock - returns current time in nanosec units.
59 * This is default implementation.
60 * Architectures and sub-architectures can override this.
61 */
62unsigned long long __weak sched_clock(void)
63{
64 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
65 * (NSEC_PER_SEC / HZ);
66}
67EXPORT_SYMBOL_GPL(sched_clock);
68
69__read_mostly int sched_clock_running;
70
71void sched_clock_init(void)
72{
73 sched_clock_running = 1;
74}
75
76#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
77/*
78 * We must start with !__sched_clock_stable because the unstable -> stable
79 * transition is accurate, while the stable -> unstable transition is not.
80 *
81 * Similarly we start with __sched_clock_stable_early, thereby assuming we
82 * will become stable, such that there's only a single 1 -> 0 transition.
83 */
84static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
85static int __sched_clock_stable_early = 1;
86
87/*
88 * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
89 */
90__read_mostly u64 __sched_clock_offset;
91static __read_mostly u64 __gtod_offset;
92
93struct sched_clock_data {
94 u64 tick_raw;
95 u64 tick_gtod;
96 u64 clock;
97};
98
99static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
100
101static inline struct sched_clock_data *this_scd(void)
102{
103 return this_cpu_ptr(&sched_clock_data);
104}
105
106static inline struct sched_clock_data *cpu_sdc(int cpu)
107{
108 return &per_cpu(sched_clock_data, cpu);
109}
110
111int sched_clock_stable(void)
112{
113 return static_branch_likely(&__sched_clock_stable);
114}
115
116static void __scd_stamp(struct sched_clock_data *scd)
117{
118 scd->tick_gtod = ktime_get_ns();
119 scd->tick_raw = sched_clock();
120}
121
122static void __set_sched_clock_stable(void)
123{
124 struct sched_clock_data *scd;
125
126 /*
127 * Since we're still unstable and the tick is already running, we have
128 * to disable IRQs in order to get a consistent scd->tick* reading.
129 */
130 local_irq_disable();
131 scd = this_scd();
132 /*
133 * Attempt to make the (initial) unstable->stable transition continuous.
134 */
135 __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
136 local_irq_enable();
137
138 printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
139 scd->tick_gtod, __gtod_offset,
140 scd->tick_raw, __sched_clock_offset);
141
142 static_branch_enable(&__sched_clock_stable);
143 tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
144}
145
146/*
147 * If we ever get here, we're screwed, because we found out -- typically after
148 * the fact -- that TSC wasn't good. This means all our clocksources (including
149 * ktime) could have reported wrong values.
150 *
151 * What we do here is an attempt to fix up and continue sort of where we left
152 * off in a coherent manner.
153 *
154 * The only way to fully avoid random clock jumps is to boot with:
155 * "tsc=unstable".
156 */
157static void __sched_clock_work(struct work_struct *work)
158{
159 struct sched_clock_data *scd;
160 int cpu;
161
162 /* take a current timestamp and set 'now' */
163 preempt_disable();
164 scd = this_scd();
165 __scd_stamp(scd);
166 scd->clock = scd->tick_gtod + __gtod_offset;
167 preempt_enable();
168
169 /* clone to all CPUs */
170 for_each_possible_cpu(cpu)
171 per_cpu(sched_clock_data, cpu) = *scd;
172
173 printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n");
174 printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
175 scd->tick_gtod, __gtod_offset,
176 scd->tick_raw, __sched_clock_offset);
177
178 static_branch_disable(&__sched_clock_stable);
179}
180
181static DECLARE_WORK(sched_clock_work, __sched_clock_work);
182
183static void __clear_sched_clock_stable(void)
184{
185 if (!sched_clock_stable())
186 return;
187
188 tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
189 schedule_work(&sched_clock_work);
190}
191
192void clear_sched_clock_stable(void)
193{
194 __sched_clock_stable_early = 0;
195
196 smp_mb(); /* matches sched_clock_init_late() */
197
198 if (sched_clock_running == 2)
199 __clear_sched_clock_stable();
200}
201
202/*
203 * We run this as late_initcall() such that it runs after all built-in drivers,
204 * notably: acpi_processor and intel_idle, which can mark the TSC as unstable.
205 */
206static int __init sched_clock_init_late(void)
207{
208 sched_clock_running = 2;
209 /*
210 * Ensure that it is impossible to not do a static_key update.
211 *
212 * Either {set,clear}_sched_clock_stable() must see sched_clock_running
213 * and do the update, or we must see their __sched_clock_stable_early
214 * and do the update, or both.
215 */
216 smp_mb(); /* matches {set,clear}_sched_clock_stable() */
217
218 if (__sched_clock_stable_early)
219 __set_sched_clock_stable();
220
221 return 0;
222}
223late_initcall(sched_clock_init_late);
224
225/*
226 * min, max except they take wrapping into account
227 */
228
229static inline u64 wrap_min(u64 x, u64 y)
230{
231 return (s64)(x - y) < 0 ? x : y;
232}
233
234static inline u64 wrap_max(u64 x, u64 y)
235{
236 return (s64)(x - y) > 0 ? x : y;
237}
238
239/*
240 * update the percpu scd from the raw @now value
241 *
242 * - filter out backward motion
243 * - use the GTOD tick value to create a window to filter crazy TSC values
244 */
245static u64 sched_clock_local(struct sched_clock_data *scd)
246{
247 u64 now, clock, old_clock, min_clock, max_clock, gtod;
248 s64 delta;
249
250again:
251 now = sched_clock();
252 delta = now - scd->tick_raw;
253 if (unlikely(delta < 0))
254 delta = 0;
255
256 old_clock = scd->clock;
257
258 /*
259 * scd->clock = clamp(scd->tick_gtod + delta,
260 * max(scd->tick_gtod, scd->clock),
261 * scd->tick_gtod + TICK_NSEC);
262 */
263
264 gtod = scd->tick_gtod + __gtod_offset;
265 clock = gtod + delta;
266 min_clock = wrap_max(gtod, old_clock);
267 max_clock = wrap_max(old_clock, gtod + TICK_NSEC);
268
269 clock = wrap_max(clock, min_clock);
270 clock = wrap_min(clock, max_clock);
271
272 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
273 goto again;
274
275 return clock;
276}
277
278static u64 sched_clock_remote(struct sched_clock_data *scd)
279{
280 struct sched_clock_data *my_scd = this_scd();
281 u64 this_clock, remote_clock;
282 u64 *ptr, old_val, val;
283
284#if BITS_PER_LONG != 64
285again:
286 /*
287 * Careful here: The local and the remote clock values need to
288 * be read out atomic as we need to compare the values and
289 * then update either the local or the remote side. So the
290 * cmpxchg64 below only protects one readout.
291 *
292 * We must reread via sched_clock_local() in the retry case on
293 * 32-bit kernels as an NMI could use sched_clock_local() via the
294 * tracer and hit between the readout of
295 * the low 32-bit and the high 32-bit portion.
296 */
297 this_clock = sched_clock_local(my_scd);
298 /*
299 * We must enforce atomic readout on 32-bit, otherwise the
300 * update on the remote CPU can hit inbetween the readout of
301 * the low 32-bit and the high 32-bit portion.
302 */
303 remote_clock = cmpxchg64(&scd->clock, 0, 0);
304#else
305 /*
306 * On 64-bit kernels the read of [my]scd->clock is atomic versus the
307 * update, so we can avoid the above 32-bit dance.
308 */
309 sched_clock_local(my_scd);
310again:
311 this_clock = my_scd->clock;
312 remote_clock = scd->clock;
313#endif
314
315 /*
316 * Use the opportunity that we have both locks
317 * taken to couple the two clocks: we take the
318 * larger time as the latest time for both
319 * runqueues. (this creates monotonic movement)
320 */
321 if (likely((s64)(remote_clock - this_clock) < 0)) {
322 ptr = &scd->clock;
323 old_val = remote_clock;
324 val = this_clock;
325 } else {
326 /*
327 * Should be rare, but possible:
328 */
329 ptr = &my_scd->clock;
330 old_val = this_clock;
331 val = remote_clock;
332 }
333
334 if (cmpxchg64(ptr, old_val, val) != old_val)
335 goto again;
336
337 return val;
338}
339
340/*
341 * Similar to cpu_clock(), but requires local IRQs to be disabled.
342 *
343 * See cpu_clock().
344 */
345u64 sched_clock_cpu(int cpu)
346{
347 struct sched_clock_data *scd;
348 u64 clock;
349
350 if (sched_clock_stable())
351 return sched_clock() + __sched_clock_offset;
352
353 if (unlikely(!sched_clock_running))
354 return 0ull;
355
356 preempt_disable_notrace();
357 scd = cpu_sdc(cpu);
358
359 if (cpu != smp_processor_id())
360 clock = sched_clock_remote(scd);
361 else
362 clock = sched_clock_local(scd);
363 preempt_enable_notrace();
364
365 return clock;
366}
367EXPORT_SYMBOL_GPL(sched_clock_cpu);
368
369void sched_clock_tick(void)
370{
371 struct sched_clock_data *scd;
372
373 if (sched_clock_stable())
374 return;
375
376 if (unlikely(!sched_clock_running))
377 return;
378
379 lockdep_assert_irqs_disabled();
380
381 scd = this_scd();
382 __scd_stamp(scd);
383 sched_clock_local(scd);
384}
385
386void sched_clock_tick_stable(void)
387{
388 u64 gtod, clock;
389
390 if (!sched_clock_stable())
391 return;
392
393 /*
394 * Called under watchdog_lock.
395 *
396 * The watchdog just found this TSC to (still) be stable, so now is a
397 * good moment to update our __gtod_offset. Because once we find the
398 * TSC to be unstable, any computation will be computing crap.
399 */
400 local_irq_disable();
401 gtod = ktime_get_ns();
402 clock = sched_clock();
403 __gtod_offset = (clock + __sched_clock_offset) - gtod;
404 local_irq_enable();
405}
406
407/*
408 * We are going deep-idle (irqs are disabled):
409 */
410void sched_clock_idle_sleep_event(void)
411{
412 sched_clock_cpu(smp_processor_id());
413}
414EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
415
416/*
417 * We just idled; resync with ktime.
418 */
419void sched_clock_idle_wakeup_event(void)
420{
421 unsigned long flags;
422
423 if (sched_clock_stable())
424 return;
425
426 if (unlikely(timekeeping_suspended))
427 return;
428
429 local_irq_save(flags);
430 sched_clock_tick();
431 local_irq_restore(flags);
432}
433EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
434
435#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
436
437u64 sched_clock_cpu(int cpu)
438{
439 if (unlikely(!sched_clock_running))
440 return 0;
441
442 return sched_clock();
443}
444
445#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
446
447/*
448 * Running clock - returns the time that has elapsed while a guest has been
449 * running.
450 * On a guest this value should be local_clock minus the time the guest was
451 * suspended by the hypervisor (for any reason).
452 * On bare metal this function should return the same as local_clock.
453 * Architectures and sub-architectures can override this.
454 */
455u64 __weak running_clock(void)
456{
457 return local_clock();
458}
1/*
2 * sched_clock for unstable cpu clocks
3 *
4 * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
5 *
6 * Updates and enhancements:
7 * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
8 *
9 * Based on code by:
10 * Ingo Molnar <mingo@redhat.com>
11 * Guillaume Chazarain <guichaz@gmail.com>
12 *
13 *
14 * What:
15 *
16 * cpu_clock(i) provides a fast (execution time) high resolution
17 * clock with bounded drift between CPUs. The value of cpu_clock(i)
18 * is monotonic for constant i. The timestamp returned is in nanoseconds.
19 *
20 * ######################### BIG FAT WARNING ##########################
21 * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
22 * # go backwards !! #
23 * ####################################################################
24 *
25 * There is no strict promise about the base, although it tends to start
26 * at 0 on boot (but people really shouldn't rely on that).
27 *
28 * cpu_clock(i) -- can be used from any context, including NMI.
29 * local_clock() -- is cpu_clock() on the current cpu.
30 *
31 * sched_clock_cpu(i)
32 *
33 * How:
34 *
35 * The implementation either uses sched_clock() when
36 * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
37 * sched_clock() is assumed to provide these properties (mostly it means
38 * the architecture provides a globally synchronized highres time source).
39 *
40 * Otherwise it tries to create a semi stable clock from a mixture of other
41 * clocks, including:
42 *
43 * - GTOD (clock monotomic)
44 * - sched_clock()
45 * - explicit idle events
46 *
47 * We use GTOD as base and use sched_clock() deltas to improve resolution. The
48 * deltas are filtered to provide monotonicity and keeping it within an
49 * expected window.
50 *
51 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
52 * that is otherwise invisible (TSC gets stopped).
53 *
54 */
55#include <linux/spinlock.h>
56#include <linux/hardirq.h>
57#include <linux/export.h>
58#include <linux/percpu.h>
59#include <linux/ktime.h>
60#include <linux/sched.h>
61#include <linux/static_key.h>
62#include <linux/workqueue.h>
63#include <linux/compiler.h>
64
65/*
66 * Scheduler clock - returns current time in nanosec units.
67 * This is default implementation.
68 * Architectures and sub-architectures can override this.
69 */
70unsigned long long __weak sched_clock(void)
71{
72 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
73 * (NSEC_PER_SEC / HZ);
74}
75EXPORT_SYMBOL_GPL(sched_clock);
76
77__read_mostly int sched_clock_running;
78
79#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
80static struct static_key __sched_clock_stable = STATIC_KEY_INIT;
81static int __sched_clock_stable_early;
82
83int sched_clock_stable(void)
84{
85 return static_key_false(&__sched_clock_stable);
86}
87
88static void __set_sched_clock_stable(void)
89{
90 if (!sched_clock_stable())
91 static_key_slow_inc(&__sched_clock_stable);
92}
93
94void set_sched_clock_stable(void)
95{
96 __sched_clock_stable_early = 1;
97
98 smp_mb(); /* matches sched_clock_init() */
99
100 if (!sched_clock_running)
101 return;
102
103 __set_sched_clock_stable();
104}
105
106static void __clear_sched_clock_stable(struct work_struct *work)
107{
108 /* XXX worry about clock continuity */
109 if (sched_clock_stable())
110 static_key_slow_dec(&__sched_clock_stable);
111}
112
113static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable);
114
115void clear_sched_clock_stable(void)
116{
117 __sched_clock_stable_early = 0;
118
119 smp_mb(); /* matches sched_clock_init() */
120
121 if (!sched_clock_running)
122 return;
123
124 schedule_work(&sched_clock_work);
125}
126
127struct sched_clock_data {
128 u64 tick_raw;
129 u64 tick_gtod;
130 u64 clock;
131};
132
133static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
134
135static inline struct sched_clock_data *this_scd(void)
136{
137 return &__get_cpu_var(sched_clock_data);
138}
139
140static inline struct sched_clock_data *cpu_sdc(int cpu)
141{
142 return &per_cpu(sched_clock_data, cpu);
143}
144
145void sched_clock_init(void)
146{
147 u64 ktime_now = ktime_to_ns(ktime_get());
148 int cpu;
149
150 for_each_possible_cpu(cpu) {
151 struct sched_clock_data *scd = cpu_sdc(cpu);
152
153 scd->tick_raw = 0;
154 scd->tick_gtod = ktime_now;
155 scd->clock = ktime_now;
156 }
157
158 sched_clock_running = 1;
159
160 /*
161 * Ensure that it is impossible to not do a static_key update.
162 *
163 * Either {set,clear}_sched_clock_stable() must see sched_clock_running
164 * and do the update, or we must see their __sched_clock_stable_early
165 * and do the update, or both.
166 */
167 smp_mb(); /* matches {set,clear}_sched_clock_stable() */
168
169 if (__sched_clock_stable_early)
170 __set_sched_clock_stable();
171 else
172 __clear_sched_clock_stable(NULL);
173}
174
175/*
176 * min, max except they take wrapping into account
177 */
178
179static inline u64 wrap_min(u64 x, u64 y)
180{
181 return (s64)(x - y) < 0 ? x : y;
182}
183
184static inline u64 wrap_max(u64 x, u64 y)
185{
186 return (s64)(x - y) > 0 ? x : y;
187}
188
189/*
190 * update the percpu scd from the raw @now value
191 *
192 * - filter out backward motion
193 * - use the GTOD tick value to create a window to filter crazy TSC values
194 */
195static u64 sched_clock_local(struct sched_clock_data *scd)
196{
197 u64 now, clock, old_clock, min_clock, max_clock;
198 s64 delta;
199
200again:
201 now = sched_clock();
202 delta = now - scd->tick_raw;
203 if (unlikely(delta < 0))
204 delta = 0;
205
206 old_clock = scd->clock;
207
208 /*
209 * scd->clock = clamp(scd->tick_gtod + delta,
210 * max(scd->tick_gtod, scd->clock),
211 * scd->tick_gtod + TICK_NSEC);
212 */
213
214 clock = scd->tick_gtod + delta;
215 min_clock = wrap_max(scd->tick_gtod, old_clock);
216 max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
217
218 clock = wrap_max(clock, min_clock);
219 clock = wrap_min(clock, max_clock);
220
221 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
222 goto again;
223
224 return clock;
225}
226
227static u64 sched_clock_remote(struct sched_clock_data *scd)
228{
229 struct sched_clock_data *my_scd = this_scd();
230 u64 this_clock, remote_clock;
231 u64 *ptr, old_val, val;
232
233#if BITS_PER_LONG != 64
234again:
235 /*
236 * Careful here: The local and the remote clock values need to
237 * be read out atomic as we need to compare the values and
238 * then update either the local or the remote side. So the
239 * cmpxchg64 below only protects one readout.
240 *
241 * We must reread via sched_clock_local() in the retry case on
242 * 32bit as an NMI could use sched_clock_local() via the
243 * tracer and hit between the readout of
244 * the low32bit and the high 32bit portion.
245 */
246 this_clock = sched_clock_local(my_scd);
247 /*
248 * We must enforce atomic readout on 32bit, otherwise the
249 * update on the remote cpu can hit inbetween the readout of
250 * the low32bit and the high 32bit portion.
251 */
252 remote_clock = cmpxchg64(&scd->clock, 0, 0);
253#else
254 /*
255 * On 64bit the read of [my]scd->clock is atomic versus the
256 * update, so we can avoid the above 32bit dance.
257 */
258 sched_clock_local(my_scd);
259again:
260 this_clock = my_scd->clock;
261 remote_clock = scd->clock;
262#endif
263
264 /*
265 * Use the opportunity that we have both locks
266 * taken to couple the two clocks: we take the
267 * larger time as the latest time for both
268 * runqueues. (this creates monotonic movement)
269 */
270 if (likely((s64)(remote_clock - this_clock) < 0)) {
271 ptr = &scd->clock;
272 old_val = remote_clock;
273 val = this_clock;
274 } else {
275 /*
276 * Should be rare, but possible:
277 */
278 ptr = &my_scd->clock;
279 old_val = this_clock;
280 val = remote_clock;
281 }
282
283 if (cmpxchg64(ptr, old_val, val) != old_val)
284 goto again;
285
286 return val;
287}
288
289/*
290 * Similar to cpu_clock(), but requires local IRQs to be disabled.
291 *
292 * See cpu_clock().
293 */
294u64 sched_clock_cpu(int cpu)
295{
296 struct sched_clock_data *scd;
297 u64 clock;
298
299 if (sched_clock_stable())
300 return sched_clock();
301
302 if (unlikely(!sched_clock_running))
303 return 0ull;
304
305 preempt_disable_notrace();
306 scd = cpu_sdc(cpu);
307
308 if (cpu != smp_processor_id())
309 clock = sched_clock_remote(scd);
310 else
311 clock = sched_clock_local(scd);
312 preempt_enable_notrace();
313
314 return clock;
315}
316
317void sched_clock_tick(void)
318{
319 struct sched_clock_data *scd;
320 u64 now, now_gtod;
321
322 if (sched_clock_stable())
323 return;
324
325 if (unlikely(!sched_clock_running))
326 return;
327
328 WARN_ON_ONCE(!irqs_disabled());
329
330 scd = this_scd();
331 now_gtod = ktime_to_ns(ktime_get());
332 now = sched_clock();
333
334 scd->tick_raw = now;
335 scd->tick_gtod = now_gtod;
336 sched_clock_local(scd);
337}
338
339/*
340 * We are going deep-idle (irqs are disabled):
341 */
342void sched_clock_idle_sleep_event(void)
343{
344 sched_clock_cpu(smp_processor_id());
345}
346EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
347
348/*
349 * We just idled delta nanoseconds (called with irqs disabled):
350 */
351void sched_clock_idle_wakeup_event(u64 delta_ns)
352{
353 if (timekeeping_suspended)
354 return;
355
356 sched_clock_tick();
357 touch_softlockup_watchdog();
358}
359EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
360
361/*
362 * As outlined at the top, provides a fast, high resolution, nanosecond
363 * time source that is monotonic per cpu argument and has bounded drift
364 * between cpus.
365 *
366 * ######################### BIG FAT WARNING ##########################
367 * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
368 * # go backwards !! #
369 * ####################################################################
370 */
371u64 cpu_clock(int cpu)
372{
373 if (!sched_clock_stable())
374 return sched_clock_cpu(cpu);
375
376 return sched_clock();
377}
378
379/*
380 * Similar to cpu_clock() for the current cpu. Time will only be observed
381 * to be monotonic if care is taken to only compare timestampt taken on the
382 * same CPU.
383 *
384 * See cpu_clock().
385 */
386u64 local_clock(void)
387{
388 if (!sched_clock_stable())
389 return sched_clock_cpu(raw_smp_processor_id());
390
391 return sched_clock();
392}
393
394#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
395
396void sched_clock_init(void)
397{
398 sched_clock_running = 1;
399}
400
401u64 sched_clock_cpu(int cpu)
402{
403 if (unlikely(!sched_clock_running))
404 return 0;
405
406 return sched_clock();
407}
408
409u64 cpu_clock(int cpu)
410{
411 return sched_clock();
412}
413
414u64 local_clock(void)
415{
416 return sched_clock();
417}
418
419#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
420
421EXPORT_SYMBOL_GPL(cpu_clock);
422EXPORT_SYMBOL_GPL(local_clock);