Loading...
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * sched_clock() for unstable CPU clocks
4 *
5 * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
6 *
7 * Updates and enhancements:
8 * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
9 *
10 * Based on code by:
11 * Ingo Molnar <mingo@redhat.com>
12 * Guillaume Chazarain <guichaz@gmail.com>
13 *
14 *
15 * What this file implements:
16 *
17 * cpu_clock(i) provides a fast (execution time) high resolution
18 * clock with bounded drift between CPUs. The value of cpu_clock(i)
19 * is monotonic for constant i. The timestamp returned is in nanoseconds.
20 *
21 * ######################### BIG FAT WARNING ##########################
22 * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
23 * # go backwards !! #
24 * ####################################################################
25 *
26 * There is no strict promise about the base, although it tends to start
27 * at 0 on boot (but people really shouldn't rely on that).
28 *
29 * cpu_clock(i) -- can be used from any context, including NMI.
30 * local_clock() -- is cpu_clock() on the current CPU.
31 *
32 * sched_clock_cpu(i)
33 *
34 * How it is implemented:
35 *
36 * The implementation either uses sched_clock() when
37 * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
38 * sched_clock() is assumed to provide these properties (mostly it means
39 * the architecture provides a globally synchronized highres time source).
40 *
41 * Otherwise it tries to create a semi stable clock from a mixture of other
42 * clocks, including:
43 *
44 * - GTOD (clock monotomic)
45 * - sched_clock()
46 * - explicit idle events
47 *
48 * We use GTOD as base and use sched_clock() deltas to improve resolution. The
49 * deltas are filtered to provide monotonicity and keeping it within an
50 * expected window.
51 *
52 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
53 * that is otherwise invisible (TSC gets stopped).
54 *
55 */
56#include "sched.h"
57#include <linux/sched_clock.h>
58
59/*
60 * Scheduler clock - returns current time in nanosec units.
61 * This is default implementation.
62 * Architectures and sub-architectures can override this.
63 */
64unsigned long long __weak sched_clock(void)
65{
66 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
67 * (NSEC_PER_SEC / HZ);
68}
69EXPORT_SYMBOL_GPL(sched_clock);
70
71static DEFINE_STATIC_KEY_FALSE(sched_clock_running);
72
73#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
74/*
75 * We must start with !__sched_clock_stable because the unstable -> stable
76 * transition is accurate, while the stable -> unstable transition is not.
77 *
78 * Similarly we start with __sched_clock_stable_early, thereby assuming we
79 * will become stable, such that there's only a single 1 -> 0 transition.
80 */
81static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
82static int __sched_clock_stable_early = 1;
83
84/*
85 * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
86 */
87__read_mostly u64 __sched_clock_offset;
88static __read_mostly u64 __gtod_offset;
89
90struct sched_clock_data {
91 u64 tick_raw;
92 u64 tick_gtod;
93 u64 clock;
94};
95
96static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
97
98static inline struct sched_clock_data *this_scd(void)
99{
100 return this_cpu_ptr(&sched_clock_data);
101}
102
103static inline struct sched_clock_data *cpu_sdc(int cpu)
104{
105 return &per_cpu(sched_clock_data, cpu);
106}
107
108int sched_clock_stable(void)
109{
110 return static_branch_likely(&__sched_clock_stable);
111}
112
113static void __scd_stamp(struct sched_clock_data *scd)
114{
115 scd->tick_gtod = ktime_get_ns();
116 scd->tick_raw = sched_clock();
117}
118
119static void __set_sched_clock_stable(void)
120{
121 struct sched_clock_data *scd;
122
123 /*
124 * Since we're still unstable and the tick is already running, we have
125 * to disable IRQs in order to get a consistent scd->tick* reading.
126 */
127 local_irq_disable();
128 scd = this_scd();
129 /*
130 * Attempt to make the (initial) unstable->stable transition continuous.
131 */
132 __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
133 local_irq_enable();
134
135 printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
136 scd->tick_gtod, __gtod_offset,
137 scd->tick_raw, __sched_clock_offset);
138
139 static_branch_enable(&__sched_clock_stable);
140 tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
141}
142
143/*
144 * If we ever get here, we're screwed, because we found out -- typically after
145 * the fact -- that TSC wasn't good. This means all our clocksources (including
146 * ktime) could have reported wrong values.
147 *
148 * What we do here is an attempt to fix up and continue sort of where we left
149 * off in a coherent manner.
150 *
151 * The only way to fully avoid random clock jumps is to boot with:
152 * "tsc=unstable".
153 */
154static void __sched_clock_work(struct work_struct *work)
155{
156 struct sched_clock_data *scd;
157 int cpu;
158
159 /* take a current timestamp and set 'now' */
160 preempt_disable();
161 scd = this_scd();
162 __scd_stamp(scd);
163 scd->clock = scd->tick_gtod + __gtod_offset;
164 preempt_enable();
165
166 /* clone to all CPUs */
167 for_each_possible_cpu(cpu)
168 per_cpu(sched_clock_data, cpu) = *scd;
169
170 printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n");
171 printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
172 scd->tick_gtod, __gtod_offset,
173 scd->tick_raw, __sched_clock_offset);
174
175 static_branch_disable(&__sched_clock_stable);
176}
177
178static DECLARE_WORK(sched_clock_work, __sched_clock_work);
179
180static void __clear_sched_clock_stable(void)
181{
182 if (!sched_clock_stable())
183 return;
184
185 tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
186 schedule_work(&sched_clock_work);
187}
188
189void clear_sched_clock_stable(void)
190{
191 __sched_clock_stable_early = 0;
192
193 smp_mb(); /* matches sched_clock_init_late() */
194
195 if (static_key_count(&sched_clock_running.key) == 2)
196 __clear_sched_clock_stable();
197}
198
199static void __sched_clock_gtod_offset(void)
200{
201 struct sched_clock_data *scd = this_scd();
202
203 __scd_stamp(scd);
204 __gtod_offset = (scd->tick_raw + __sched_clock_offset) - scd->tick_gtod;
205}
206
207void __init sched_clock_init(void)
208{
209 /*
210 * Set __gtod_offset such that once we mark sched_clock_running,
211 * sched_clock_tick() continues where sched_clock() left off.
212 *
213 * Even if TSC is buggered, we're still UP at this point so it
214 * can't really be out of sync.
215 */
216 local_irq_disable();
217 __sched_clock_gtod_offset();
218 local_irq_enable();
219
220 static_branch_inc(&sched_clock_running);
221}
222/*
223 * We run this as late_initcall() such that it runs after all built-in drivers,
224 * notably: acpi_processor and intel_idle, which can mark the TSC as unstable.
225 */
226static int __init sched_clock_init_late(void)
227{
228 static_branch_inc(&sched_clock_running);
229 /*
230 * Ensure that it is impossible to not do a static_key update.
231 *
232 * Either {set,clear}_sched_clock_stable() must see sched_clock_running
233 * and do the update, or we must see their __sched_clock_stable_early
234 * and do the update, or both.
235 */
236 smp_mb(); /* matches {set,clear}_sched_clock_stable() */
237
238 if (__sched_clock_stable_early)
239 __set_sched_clock_stable();
240
241 return 0;
242}
243late_initcall(sched_clock_init_late);
244
245/*
246 * min, max except they take wrapping into account
247 */
248
249static inline u64 wrap_min(u64 x, u64 y)
250{
251 return (s64)(x - y) < 0 ? x : y;
252}
253
254static inline u64 wrap_max(u64 x, u64 y)
255{
256 return (s64)(x - y) > 0 ? x : y;
257}
258
259/*
260 * update the percpu scd from the raw @now value
261 *
262 * - filter out backward motion
263 * - use the GTOD tick value to create a window to filter crazy TSC values
264 */
265static u64 sched_clock_local(struct sched_clock_data *scd)
266{
267 u64 now, clock, old_clock, min_clock, max_clock, gtod;
268 s64 delta;
269
270again:
271 now = sched_clock();
272 delta = now - scd->tick_raw;
273 if (unlikely(delta < 0))
274 delta = 0;
275
276 old_clock = scd->clock;
277
278 /*
279 * scd->clock = clamp(scd->tick_gtod + delta,
280 * max(scd->tick_gtod, scd->clock),
281 * scd->tick_gtod + TICK_NSEC);
282 */
283
284 gtod = scd->tick_gtod + __gtod_offset;
285 clock = gtod + delta;
286 min_clock = wrap_max(gtod, old_clock);
287 max_clock = wrap_max(old_clock, gtod + TICK_NSEC);
288
289 clock = wrap_max(clock, min_clock);
290 clock = wrap_min(clock, max_clock);
291
292 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
293 goto again;
294
295 return clock;
296}
297
298static u64 sched_clock_remote(struct sched_clock_data *scd)
299{
300 struct sched_clock_data *my_scd = this_scd();
301 u64 this_clock, remote_clock;
302 u64 *ptr, old_val, val;
303
304#if BITS_PER_LONG != 64
305again:
306 /*
307 * Careful here: The local and the remote clock values need to
308 * be read out atomic as we need to compare the values and
309 * then update either the local or the remote side. So the
310 * cmpxchg64 below only protects one readout.
311 *
312 * We must reread via sched_clock_local() in the retry case on
313 * 32-bit kernels as an NMI could use sched_clock_local() via the
314 * tracer and hit between the readout of
315 * the low 32-bit and the high 32-bit portion.
316 */
317 this_clock = sched_clock_local(my_scd);
318 /*
319 * We must enforce atomic readout on 32-bit, otherwise the
320 * update on the remote CPU can hit inbetween the readout of
321 * the low 32-bit and the high 32-bit portion.
322 */
323 remote_clock = cmpxchg64(&scd->clock, 0, 0);
324#else
325 /*
326 * On 64-bit kernels the read of [my]scd->clock is atomic versus the
327 * update, so we can avoid the above 32-bit dance.
328 */
329 sched_clock_local(my_scd);
330again:
331 this_clock = my_scd->clock;
332 remote_clock = scd->clock;
333#endif
334
335 /*
336 * Use the opportunity that we have both locks
337 * taken to couple the two clocks: we take the
338 * larger time as the latest time for both
339 * runqueues. (this creates monotonic movement)
340 */
341 if (likely((s64)(remote_clock - this_clock) < 0)) {
342 ptr = &scd->clock;
343 old_val = remote_clock;
344 val = this_clock;
345 } else {
346 /*
347 * Should be rare, but possible:
348 */
349 ptr = &my_scd->clock;
350 old_val = this_clock;
351 val = remote_clock;
352 }
353
354 if (cmpxchg64(ptr, old_val, val) != old_val)
355 goto again;
356
357 return val;
358}
359
360/*
361 * Similar to cpu_clock(), but requires local IRQs to be disabled.
362 *
363 * See cpu_clock().
364 */
365u64 sched_clock_cpu(int cpu)
366{
367 struct sched_clock_data *scd;
368 u64 clock;
369
370 if (sched_clock_stable())
371 return sched_clock() + __sched_clock_offset;
372
373 if (!static_branch_unlikely(&sched_clock_running))
374 return sched_clock();
375
376 preempt_disable_notrace();
377 scd = cpu_sdc(cpu);
378
379 if (cpu != smp_processor_id())
380 clock = sched_clock_remote(scd);
381 else
382 clock = sched_clock_local(scd);
383 preempt_enable_notrace();
384
385 return clock;
386}
387EXPORT_SYMBOL_GPL(sched_clock_cpu);
388
389void sched_clock_tick(void)
390{
391 struct sched_clock_data *scd;
392
393 if (sched_clock_stable())
394 return;
395
396 if (!static_branch_unlikely(&sched_clock_running))
397 return;
398
399 lockdep_assert_irqs_disabled();
400
401 scd = this_scd();
402 __scd_stamp(scd);
403 sched_clock_local(scd);
404}
405
406void sched_clock_tick_stable(void)
407{
408 if (!sched_clock_stable())
409 return;
410
411 /*
412 * Called under watchdog_lock.
413 *
414 * The watchdog just found this TSC to (still) be stable, so now is a
415 * good moment to update our __gtod_offset. Because once we find the
416 * TSC to be unstable, any computation will be computing crap.
417 */
418 local_irq_disable();
419 __sched_clock_gtod_offset();
420 local_irq_enable();
421}
422
423/*
424 * We are going deep-idle (irqs are disabled):
425 */
426void sched_clock_idle_sleep_event(void)
427{
428 sched_clock_cpu(smp_processor_id());
429}
430EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
431
432/*
433 * We just idled; resync with ktime.
434 */
435void sched_clock_idle_wakeup_event(void)
436{
437 unsigned long flags;
438
439 if (sched_clock_stable())
440 return;
441
442 if (unlikely(timekeeping_suspended))
443 return;
444
445 local_irq_save(flags);
446 sched_clock_tick();
447 local_irq_restore(flags);
448}
449EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
450
451#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
452
453void __init sched_clock_init(void)
454{
455 static_branch_inc(&sched_clock_running);
456 local_irq_disable();
457 generic_sched_clock_init();
458 local_irq_enable();
459}
460
461u64 sched_clock_cpu(int cpu)
462{
463 if (!static_branch_unlikely(&sched_clock_running))
464 return 0;
465
466 return sched_clock();
467}
468
469#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
470
471/*
472 * Running clock - returns the time that has elapsed while a guest has been
473 * running.
474 * On a guest this value should be local_clock minus the time the guest was
475 * suspended by the hypervisor (for any reason).
476 * On bare metal this function should return the same as local_clock.
477 * Architectures and sub-architectures can override this.
478 */
479u64 __weak running_clock(void)
480{
481 return local_clock();
482}
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}