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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:
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#include <linux/tick.h>
65
66/*
67 * Scheduler clock - returns current time in nanosec units.
68 * This is default implementation.
69 * Architectures and sub-architectures can override this.
70 */
71unsigned long long __weak sched_clock(void)
72{
73 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
74 * (NSEC_PER_SEC / HZ);
75}
76EXPORT_SYMBOL_GPL(sched_clock);
77
78__read_mostly int sched_clock_running;
79
80#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
81static struct static_key __sched_clock_stable = STATIC_KEY_INIT;
82static int __sched_clock_stable_early;
83
84int sched_clock_stable(void)
85{
86 return static_key_false(&__sched_clock_stable);
87}
88
89static void __set_sched_clock_stable(void)
90{
91 if (!sched_clock_stable())
92 static_key_slow_inc(&__sched_clock_stable);
93
94 tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
95}
96
97void set_sched_clock_stable(void)
98{
99 __sched_clock_stable_early = 1;
100
101 smp_mb(); /* matches sched_clock_init() */
102
103 if (!sched_clock_running)
104 return;
105
106 __set_sched_clock_stable();
107}
108
109static void __clear_sched_clock_stable(struct work_struct *work)
110{
111 /* XXX worry about clock continuity */
112 if (sched_clock_stable())
113 static_key_slow_dec(&__sched_clock_stable);
114
115 tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
116}
117
118static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable);
119
120void clear_sched_clock_stable(void)
121{
122 __sched_clock_stable_early = 0;
123
124 smp_mb(); /* matches sched_clock_init() */
125
126 if (!sched_clock_running)
127 return;
128
129 schedule_work(&sched_clock_work);
130}
131
132struct sched_clock_data {
133 u64 tick_raw;
134 u64 tick_gtod;
135 u64 clock;
136};
137
138static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
139
140static inline struct sched_clock_data *this_scd(void)
141{
142 return this_cpu_ptr(&sched_clock_data);
143}
144
145static inline struct sched_clock_data *cpu_sdc(int cpu)
146{
147 return &per_cpu(sched_clock_data, cpu);
148}
149
150void sched_clock_init(void)
151{
152 u64 ktime_now = ktime_to_ns(ktime_get());
153 int cpu;
154
155 for_each_possible_cpu(cpu) {
156 struct sched_clock_data *scd = cpu_sdc(cpu);
157
158 scd->tick_raw = 0;
159 scd->tick_gtod = ktime_now;
160 scd->clock = ktime_now;
161 }
162
163 sched_clock_running = 1;
164
165 /*
166 * Ensure that it is impossible to not do a static_key update.
167 *
168 * Either {set,clear}_sched_clock_stable() must see sched_clock_running
169 * and do the update, or we must see their __sched_clock_stable_early
170 * and do the update, or both.
171 */
172 smp_mb(); /* matches {set,clear}_sched_clock_stable() */
173
174 if (__sched_clock_stable_early)
175 __set_sched_clock_stable();
176 else
177 __clear_sched_clock_stable(NULL);
178}
179
180/*
181 * min, max except they take wrapping into account
182 */
183
184static inline u64 wrap_min(u64 x, u64 y)
185{
186 return (s64)(x - y) < 0 ? x : y;
187}
188
189static inline u64 wrap_max(u64 x, u64 y)
190{
191 return (s64)(x - y) > 0 ? x : y;
192}
193
194/*
195 * update the percpu scd from the raw @now value
196 *
197 * - filter out backward motion
198 * - use the GTOD tick value to create a window to filter crazy TSC values
199 */
200static u64 sched_clock_local(struct sched_clock_data *scd)
201{
202 u64 now, clock, old_clock, min_clock, max_clock;
203 s64 delta;
204
205again:
206 now = sched_clock();
207 delta = now - scd->tick_raw;
208 if (unlikely(delta < 0))
209 delta = 0;
210
211 old_clock = scd->clock;
212
213 /*
214 * scd->clock = clamp(scd->tick_gtod + delta,
215 * max(scd->tick_gtod, scd->clock),
216 * scd->tick_gtod + TICK_NSEC);
217 */
218
219 clock = scd->tick_gtod + delta;
220 min_clock = wrap_max(scd->tick_gtod, old_clock);
221 max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
222
223 clock = wrap_max(clock, min_clock);
224 clock = wrap_min(clock, max_clock);
225
226 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
227 goto again;
228
229 return clock;
230}
231
232static u64 sched_clock_remote(struct sched_clock_data *scd)
233{
234 struct sched_clock_data *my_scd = this_scd();
235 u64 this_clock, remote_clock;
236 u64 *ptr, old_val, val;
237
238#if BITS_PER_LONG != 64
239again:
240 /*
241 * Careful here: The local and the remote clock values need to
242 * be read out atomic as we need to compare the values and
243 * then update either the local or the remote side. So the
244 * cmpxchg64 below only protects one readout.
245 *
246 * We must reread via sched_clock_local() in the retry case on
247 * 32bit as an NMI could use sched_clock_local() via the
248 * tracer and hit between the readout of
249 * the low32bit and the high 32bit portion.
250 */
251 this_clock = sched_clock_local(my_scd);
252 /*
253 * We must enforce atomic readout on 32bit, otherwise the
254 * update on the remote cpu can hit inbetween the readout of
255 * the low32bit and the high 32bit portion.
256 */
257 remote_clock = cmpxchg64(&scd->clock, 0, 0);
258#else
259 /*
260 * On 64bit the read of [my]scd->clock is atomic versus the
261 * update, so we can avoid the above 32bit dance.
262 */
263 sched_clock_local(my_scd);
264again:
265 this_clock = my_scd->clock;
266 remote_clock = scd->clock;
267#endif
268
269 /*
270 * Use the opportunity that we have both locks
271 * taken to couple the two clocks: we take the
272 * larger time as the latest time for both
273 * runqueues. (this creates monotonic movement)
274 */
275 if (likely((s64)(remote_clock - this_clock) < 0)) {
276 ptr = &scd->clock;
277 old_val = remote_clock;
278 val = this_clock;
279 } else {
280 /*
281 * Should be rare, but possible:
282 */
283 ptr = &my_scd->clock;
284 old_val = this_clock;
285 val = remote_clock;
286 }
287
288 if (cmpxchg64(ptr, old_val, val) != old_val)
289 goto again;
290
291 return val;
292}
293
294/*
295 * Similar to cpu_clock(), but requires local IRQs to be disabled.
296 *
297 * See cpu_clock().
298 */
299u64 sched_clock_cpu(int cpu)
300{
301 struct sched_clock_data *scd;
302 u64 clock;
303
304 if (sched_clock_stable())
305 return sched_clock();
306
307 if (unlikely(!sched_clock_running))
308 return 0ull;
309
310 preempt_disable_notrace();
311 scd = cpu_sdc(cpu);
312
313 if (cpu != smp_processor_id())
314 clock = sched_clock_remote(scd);
315 else
316 clock = sched_clock_local(scd);
317 preempt_enable_notrace();
318
319 return clock;
320}
321
322void sched_clock_tick(void)
323{
324 struct sched_clock_data *scd;
325 u64 now, now_gtod;
326
327 if (sched_clock_stable())
328 return;
329
330 if (unlikely(!sched_clock_running))
331 return;
332
333 WARN_ON_ONCE(!irqs_disabled());
334
335 scd = this_scd();
336 now_gtod = ktime_to_ns(ktime_get());
337 now = sched_clock();
338
339 scd->tick_raw = now;
340 scd->tick_gtod = now_gtod;
341 sched_clock_local(scd);
342}
343
344/*
345 * We are going deep-idle (irqs are disabled):
346 */
347void sched_clock_idle_sleep_event(void)
348{
349 sched_clock_cpu(smp_processor_id());
350}
351EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
352
353/*
354 * We just idled delta nanoseconds (called with irqs disabled):
355 */
356void sched_clock_idle_wakeup_event(u64 delta_ns)
357{
358 if (timekeeping_suspended)
359 return;
360
361 sched_clock_tick();
362 touch_softlockup_watchdog_sched();
363}
364EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
365
366/*
367 * As outlined at the top, provides a fast, high resolution, nanosecond
368 * time source that is monotonic per cpu argument and has bounded drift
369 * between cpus.
370 *
371 * ######################### BIG FAT WARNING ##########################
372 * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
373 * # go backwards !! #
374 * ####################################################################
375 */
376u64 cpu_clock(int cpu)
377{
378 if (!sched_clock_stable())
379 return sched_clock_cpu(cpu);
380
381 return sched_clock();
382}
383
384/*
385 * Similar to cpu_clock() for the current cpu. Time will only be observed
386 * to be monotonic if care is taken to only compare timestampt taken on the
387 * same CPU.
388 *
389 * See cpu_clock().
390 */
391u64 local_clock(void)
392{
393 if (!sched_clock_stable())
394 return sched_clock_cpu(raw_smp_processor_id());
395
396 return sched_clock();
397}
398
399#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
400
401void sched_clock_init(void)
402{
403 sched_clock_running = 1;
404}
405
406u64 sched_clock_cpu(int cpu)
407{
408 if (unlikely(!sched_clock_running))
409 return 0;
410
411 return sched_clock();
412}
413
414u64 cpu_clock(int cpu)
415{
416 return sched_clock();
417}
418
419u64 local_clock(void)
420{
421 return sched_clock();
422}
423
424#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
425
426EXPORT_SYMBOL_GPL(cpu_clock);
427EXPORT_SYMBOL_GPL(local_clock);
428
429/*
430 * Running clock - returns the time that has elapsed while a guest has been
431 * running.
432 * On a guest this value should be local_clock minus the time the guest was
433 * suspended by the hypervisor (for any reason).
434 * On bare metal this function should return the same as local_clock.
435 * Architectures and sub-architectures can override this.
436 */
437u64 __weak running_clock(void)
438{
439 return local_clock();
440}
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 * sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI)
30 * local_clock() -- is cpu_clock() on the current cpu.
31 *
32 * How:
33 *
34 * The implementation either uses sched_clock() when
35 * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
36 * sched_clock() is assumed to provide these properties (mostly it means
37 * the architecture provides a globally synchronized highres time source).
38 *
39 * Otherwise it tries to create a semi stable clock from a mixture of other
40 * clocks, including:
41 *
42 * - GTOD (clock monotomic)
43 * - sched_clock()
44 * - explicit idle events
45 *
46 * We use GTOD as base and use sched_clock() deltas to improve resolution. The
47 * deltas are filtered to provide monotonicity and keeping it within an
48 * expected window.
49 *
50 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
51 * that is otherwise invisible (TSC gets stopped).
52 *
53 *
54 * Notes:
55 *
56 * The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things
57 * like cpufreq interrupts that can change the base clock (TSC) multiplier
58 * and cause funny jumps in time -- although the filtering provided by
59 * sched_clock_cpu() should mitigate serious artifacts we cannot rely on it
60 * in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on
61 * sched_clock().
62 */
63#include <linux/spinlock.h>
64#include <linux/hardirq.h>
65#include <linux/export.h>
66#include <linux/percpu.h>
67#include <linux/ktime.h>
68#include <linux/sched.h>
69
70/*
71 * Scheduler clock - returns current time in nanosec units.
72 * This is default implementation.
73 * Architectures and sub-architectures can override this.
74 */
75unsigned long long __attribute__((weak)) sched_clock(void)
76{
77 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
78 * (NSEC_PER_SEC / HZ);
79}
80EXPORT_SYMBOL_GPL(sched_clock);
81
82__read_mostly int sched_clock_running;
83
84#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
85__read_mostly int sched_clock_stable;
86
87struct sched_clock_data {
88 u64 tick_raw;
89 u64 tick_gtod;
90 u64 clock;
91};
92
93static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
94
95static inline struct sched_clock_data *this_scd(void)
96{
97 return &__get_cpu_var(sched_clock_data);
98}
99
100static inline struct sched_clock_data *cpu_sdc(int cpu)
101{
102 return &per_cpu(sched_clock_data, cpu);
103}
104
105void sched_clock_init(void)
106{
107 u64 ktime_now = ktime_to_ns(ktime_get());
108 int cpu;
109
110 for_each_possible_cpu(cpu) {
111 struct sched_clock_data *scd = cpu_sdc(cpu);
112
113 scd->tick_raw = 0;
114 scd->tick_gtod = ktime_now;
115 scd->clock = ktime_now;
116 }
117
118 sched_clock_running = 1;
119}
120
121/*
122 * min, max except they take wrapping into account
123 */
124
125static inline u64 wrap_min(u64 x, u64 y)
126{
127 return (s64)(x - y) < 0 ? x : y;
128}
129
130static inline u64 wrap_max(u64 x, u64 y)
131{
132 return (s64)(x - y) > 0 ? x : y;
133}
134
135/*
136 * update the percpu scd from the raw @now value
137 *
138 * - filter out backward motion
139 * - use the GTOD tick value to create a window to filter crazy TSC values
140 */
141static u64 sched_clock_local(struct sched_clock_data *scd)
142{
143 u64 now, clock, old_clock, min_clock, max_clock;
144 s64 delta;
145
146again:
147 now = sched_clock();
148 delta = now - scd->tick_raw;
149 if (unlikely(delta < 0))
150 delta = 0;
151
152 old_clock = scd->clock;
153
154 /*
155 * scd->clock = clamp(scd->tick_gtod + delta,
156 * max(scd->tick_gtod, scd->clock),
157 * scd->tick_gtod + TICK_NSEC);
158 */
159
160 clock = scd->tick_gtod + delta;
161 min_clock = wrap_max(scd->tick_gtod, old_clock);
162 max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
163
164 clock = wrap_max(clock, min_clock);
165 clock = wrap_min(clock, max_clock);
166
167 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
168 goto again;
169
170 return clock;
171}
172
173static u64 sched_clock_remote(struct sched_clock_data *scd)
174{
175 struct sched_clock_data *my_scd = this_scd();
176 u64 this_clock, remote_clock;
177 u64 *ptr, old_val, val;
178
179 sched_clock_local(my_scd);
180again:
181 this_clock = my_scd->clock;
182 remote_clock = scd->clock;
183
184 /*
185 * Use the opportunity that we have both locks
186 * taken to couple the two clocks: we take the
187 * larger time as the latest time for both
188 * runqueues. (this creates monotonic movement)
189 */
190 if (likely((s64)(remote_clock - this_clock) < 0)) {
191 ptr = &scd->clock;
192 old_val = remote_clock;
193 val = this_clock;
194 } else {
195 /*
196 * Should be rare, but possible:
197 */
198 ptr = &my_scd->clock;
199 old_val = this_clock;
200 val = remote_clock;
201 }
202
203 if (cmpxchg64(ptr, old_val, val) != old_val)
204 goto again;
205
206 return val;
207}
208
209/*
210 * Similar to cpu_clock(), but requires local IRQs to be disabled.
211 *
212 * See cpu_clock().
213 */
214u64 sched_clock_cpu(int cpu)
215{
216 struct sched_clock_data *scd;
217 u64 clock;
218
219 WARN_ON_ONCE(!irqs_disabled());
220
221 if (sched_clock_stable)
222 return sched_clock();
223
224 if (unlikely(!sched_clock_running))
225 return 0ull;
226
227 scd = cpu_sdc(cpu);
228
229 if (cpu != smp_processor_id())
230 clock = sched_clock_remote(scd);
231 else
232 clock = sched_clock_local(scd);
233
234 return clock;
235}
236
237void sched_clock_tick(void)
238{
239 struct sched_clock_data *scd;
240 u64 now, now_gtod;
241
242 if (sched_clock_stable)
243 return;
244
245 if (unlikely(!sched_clock_running))
246 return;
247
248 WARN_ON_ONCE(!irqs_disabled());
249
250 scd = this_scd();
251 now_gtod = ktime_to_ns(ktime_get());
252 now = sched_clock();
253
254 scd->tick_raw = now;
255 scd->tick_gtod = now_gtod;
256 sched_clock_local(scd);
257}
258
259/*
260 * We are going deep-idle (irqs are disabled):
261 */
262void sched_clock_idle_sleep_event(void)
263{
264 sched_clock_cpu(smp_processor_id());
265}
266EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
267
268/*
269 * We just idled delta nanoseconds (called with irqs disabled):
270 */
271void sched_clock_idle_wakeup_event(u64 delta_ns)
272{
273 if (timekeeping_suspended)
274 return;
275
276 sched_clock_tick();
277 touch_softlockup_watchdog();
278}
279EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
280
281/*
282 * As outlined at the top, provides a fast, high resolution, nanosecond
283 * time source that is monotonic per cpu argument and has bounded drift
284 * between cpus.
285 *
286 * ######################### BIG FAT WARNING ##########################
287 * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
288 * # go backwards !! #
289 * ####################################################################
290 */
291u64 cpu_clock(int cpu)
292{
293 u64 clock;
294 unsigned long flags;
295
296 local_irq_save(flags);
297 clock = sched_clock_cpu(cpu);
298 local_irq_restore(flags);
299
300 return clock;
301}
302
303/*
304 * Similar to cpu_clock() for the current cpu. Time will only be observed
305 * to be monotonic if care is taken to only compare timestampt taken on the
306 * same CPU.
307 *
308 * See cpu_clock().
309 */
310u64 local_clock(void)
311{
312 u64 clock;
313 unsigned long flags;
314
315 local_irq_save(flags);
316 clock = sched_clock_cpu(smp_processor_id());
317 local_irq_restore(flags);
318
319 return clock;
320}
321
322#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
323
324void sched_clock_init(void)
325{
326 sched_clock_running = 1;
327}
328
329u64 sched_clock_cpu(int cpu)
330{
331 if (unlikely(!sched_clock_running))
332 return 0;
333
334 return sched_clock();
335}
336
337u64 cpu_clock(int cpu)
338{
339 return sched_clock_cpu(cpu);
340}
341
342u64 local_clock(void)
343{
344 return sched_clock_cpu(0);
345}
346
347#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
348
349EXPORT_SYMBOL_GPL(cpu_clock);
350EXPORT_SYMBOL_GPL(local_clock);