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Commit | Line | Data |
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3e51f33f PZ |
1 | /* |
2 | * sched_clock for unstable cpu clocks | |
3 | * | |
90eec103 | 4 | * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra |
3e51f33f | 5 | * |
c300ba25 SR |
6 | * Updates and enhancements: |
7 | * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com> | |
8 | * | |
3e51f33f PZ |
9 | * Based on code by: |
10 | * Ingo Molnar <mingo@redhat.com> | |
11 | * Guillaume Chazarain <guichaz@gmail.com> | |
12 | * | |
c676329a PZ |
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. | |
c676329a PZ |
29 | * local_clock() -- is cpu_clock() on the current cpu. |
30 | * | |
ef08f0ff PZ |
31 | * sched_clock_cpu(i) |
32 | * | |
c676329a PZ |
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) | |
3e51f33f PZ |
44 | * - sched_clock() |
45 | * - explicit idle events | |
46 | * | |
c676329a PZ |
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. | |
3e51f33f PZ |
50 | * |
51 | * Furthermore, explicit sleep and wakeup hooks allow us to account for time | |
52 | * that is otherwise invisible (TSC gets stopped). | |
53 | * | |
3e51f33f | 54 | */ |
3e51f33f | 55 | #include <linux/spinlock.h> |
6409c4da | 56 | #include <linux/hardirq.h> |
9984de1a | 57 | #include <linux/export.h> |
b342501c IM |
58 | #include <linux/percpu.h> |
59 | #include <linux/ktime.h> | |
60 | #include <linux/sched.h> | |
38b8d208 | 61 | #include <linux/nmi.h> |
e6017571 | 62 | #include <linux/sched/clock.h> |
35af99e6 | 63 | #include <linux/static_key.h> |
6577e42a | 64 | #include <linux/workqueue.h> |
52f5684c | 65 | #include <linux/compiler.h> |
4f49b90a | 66 | #include <linux/tick.h> |
2e44b7dd | 67 | #include <linux/init.h> |
3e51f33f | 68 | |
2c3d103b HD |
69 | /* |
70 | * Scheduler clock - returns current time in nanosec units. | |
71 | * This is default implementation. | |
72 | * Architectures and sub-architectures can override this. | |
73 | */ | |
52f5684c | 74 | unsigned long long __weak sched_clock(void) |
2c3d103b | 75 | { |
92d23f70 R |
76 | return (unsigned long long)(jiffies - INITIAL_JIFFIES) |
77 | * (NSEC_PER_SEC / HZ); | |
2c3d103b | 78 | } |
b6ac23af | 79 | EXPORT_SYMBOL_GPL(sched_clock); |
3e51f33f | 80 | |
5bb6b1ea | 81 | __read_mostly int sched_clock_running; |
c1955a3d | 82 | |
9881b024 PZ |
83 | void sched_clock_init(void) |
84 | { | |
85 | sched_clock_running = 1; | |
86 | } | |
87 | ||
3e51f33f | 88 | #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK |
acb04058 PZ |
89 | /* |
90 | * We must start with !__sched_clock_stable because the unstable -> stable | |
91 | * transition is accurate, while the stable -> unstable transition is not. | |
92 | * | |
93 | * Similarly we start with __sched_clock_stable_early, thereby assuming we | |
94 | * will become stable, such that there's only a single 1 -> 0 transition. | |
95 | */ | |
555570d7 | 96 | static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable); |
acb04058 | 97 | static int __sched_clock_stable_early = 1; |
35af99e6 | 98 | |
5680d809 | 99 | /* |
698eff63 | 100 | * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset |
5680d809 | 101 | */ |
698eff63 PZ |
102 | __read_mostly u64 __sched_clock_offset; |
103 | static __read_mostly u64 __gtod_offset; | |
5680d809 PZ |
104 | |
105 | struct sched_clock_data { | |
106 | u64 tick_raw; | |
107 | u64 tick_gtod; | |
108 | u64 clock; | |
109 | }; | |
110 | ||
111 | static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); | |
112 | ||
113 | static inline struct sched_clock_data *this_scd(void) | |
114 | { | |
115 | return this_cpu_ptr(&sched_clock_data); | |
116 | } | |
117 | ||
118 | static inline struct sched_clock_data *cpu_sdc(int cpu) | |
119 | { | |
120 | return &per_cpu(sched_clock_data, cpu); | |
121 | } | |
122 | ||
35af99e6 PZ |
123 | int sched_clock_stable(void) |
124 | { | |
555570d7 | 125 | return static_branch_likely(&__sched_clock_stable); |
35af99e6 PZ |
126 | } |
127 | ||
cf15ca8d PZ |
128 | static void __scd_stamp(struct sched_clock_data *scd) |
129 | { | |
130 | scd->tick_gtod = ktime_get_ns(); | |
131 | scd->tick_raw = sched_clock(); | |
132 | } | |
133 | ||
d375b4e0 | 134 | static void __set_sched_clock_stable(void) |
35af99e6 | 135 | { |
5680d809 PZ |
136 | struct sched_clock_data *scd = this_scd(); |
137 | ||
138 | /* | |
139 | * Attempt to make the (initial) unstable->stable transition continuous. | |
140 | */ | |
698eff63 | 141 | __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw); |
5680d809 PZ |
142 | |
143 | printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n", | |
698eff63 PZ |
144 | scd->tick_gtod, __gtod_offset, |
145 | scd->tick_raw, __sched_clock_offset); | |
5680d809 | 146 | |
555570d7 | 147 | static_branch_enable(&__sched_clock_stable); |
4f49b90a | 148 | tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE); |
d375b4e0 PZ |
149 | } |
150 | ||
cf15ca8d PZ |
151 | /* |
152 | * If we ever get here, we're screwed, because we found out -- typically after | |
153 | * the fact -- that TSC wasn't good. This means all our clocksources (including | |
154 | * ktime) could have reported wrong values. | |
155 | * | |
156 | * What we do here is an attempt to fix up and continue sort of where we left | |
157 | * off in a coherent manner. | |
158 | * | |
159 | * The only way to fully avoid random clock jumps is to boot with: | |
160 | * "tsc=unstable". | |
161 | */ | |
71fdb70e PZ |
162 | static void __sched_clock_work(struct work_struct *work) |
163 | { | |
cf15ca8d PZ |
164 | struct sched_clock_data *scd; |
165 | int cpu; | |
166 | ||
167 | /* take a current timestamp and set 'now' */ | |
168 | preempt_disable(); | |
169 | scd = this_scd(); | |
170 | __scd_stamp(scd); | |
171 | scd->clock = scd->tick_gtod + __gtod_offset; | |
172 | preempt_enable(); | |
173 | ||
174 | /* clone to all CPUs */ | |
175 | for_each_possible_cpu(cpu) | |
176 | per_cpu(sched_clock_data, cpu) = *scd; | |
177 | ||
7708d5f0 | 178 | printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n"); |
cf15ca8d PZ |
179 | printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", |
180 | scd->tick_gtod, __gtod_offset, | |
181 | scd->tick_raw, __sched_clock_offset); | |
182 | ||
71fdb70e PZ |
183 | static_branch_disable(&__sched_clock_stable); |
184 | } | |
185 | ||
186 | static DECLARE_WORK(sched_clock_work, __sched_clock_work); | |
187 | ||
188 | static void __clear_sched_clock_stable(void) | |
35af99e6 | 189 | { |
cf15ca8d PZ |
190 | if (!sched_clock_stable()) |
191 | return; | |
5680d809 | 192 | |
4f49b90a | 193 | tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE); |
cf15ca8d | 194 | schedule_work(&sched_clock_work); |
71fdb70e | 195 | } |
6577e42a PZ |
196 | |
197 | void clear_sched_clock_stable(void) | |
198 | { | |
d375b4e0 PZ |
199 | __sched_clock_stable_early = 0; |
200 | ||
9881b024 | 201 | smp_mb(); /* matches sched_clock_init_late() */ |
d375b4e0 | 202 | |
9881b024 | 203 | if (sched_clock_running == 2) |
71fdb70e | 204 | __clear_sched_clock_stable(); |
6577e42a PZ |
205 | } |
206 | ||
2e44b7dd PZ |
207 | /* |
208 | * We run this as late_initcall() such that it runs after all built-in drivers, | |
209 | * notably: acpi_processor and intel_idle, which can mark the TSC as unstable. | |
210 | */ | |
211 | static int __init sched_clock_init_late(void) | |
3e51f33f | 212 | { |
9881b024 | 213 | sched_clock_running = 2; |
d375b4e0 PZ |
214 | /* |
215 | * Ensure that it is impossible to not do a static_key update. | |
216 | * | |
217 | * Either {set,clear}_sched_clock_stable() must see sched_clock_running | |
218 | * and do the update, or we must see their __sched_clock_stable_early | |
219 | * and do the update, or both. | |
220 | */ | |
221 | smp_mb(); /* matches {set,clear}_sched_clock_stable() */ | |
222 | ||
223 | if (__sched_clock_stable_early) | |
224 | __set_sched_clock_stable(); | |
2e44b7dd PZ |
225 | |
226 | return 0; | |
3e51f33f | 227 | } |
2e44b7dd | 228 | late_initcall(sched_clock_init_late); |
3e51f33f | 229 | |
354879bb | 230 | /* |
b342501c | 231 | * min, max except they take wrapping into account |
354879bb PZ |
232 | */ |
233 | ||
234 | static inline u64 wrap_min(u64 x, u64 y) | |
235 | { | |
236 | return (s64)(x - y) < 0 ? x : y; | |
237 | } | |
238 | ||
239 | static inline u64 wrap_max(u64 x, u64 y) | |
240 | { | |
241 | return (s64)(x - y) > 0 ? x : y; | |
242 | } | |
243 | ||
3e51f33f PZ |
244 | /* |
245 | * update the percpu scd from the raw @now value | |
246 | * | |
247 | * - filter out backward motion | |
354879bb | 248 | * - use the GTOD tick value to create a window to filter crazy TSC values |
3e51f33f | 249 | */ |
def0a9b2 | 250 | static u64 sched_clock_local(struct sched_clock_data *scd) |
3e51f33f | 251 | { |
7b09cc5a | 252 | u64 now, clock, old_clock, min_clock, max_clock, gtod; |
def0a9b2 | 253 | s64 delta; |
3e51f33f | 254 | |
def0a9b2 PZ |
255 | again: |
256 | now = sched_clock(); | |
257 | delta = now - scd->tick_raw; | |
354879bb PZ |
258 | if (unlikely(delta < 0)) |
259 | delta = 0; | |
3e51f33f | 260 | |
def0a9b2 PZ |
261 | old_clock = scd->clock; |
262 | ||
354879bb PZ |
263 | /* |
264 | * scd->clock = clamp(scd->tick_gtod + delta, | |
b342501c IM |
265 | * max(scd->tick_gtod, scd->clock), |
266 | * scd->tick_gtod + TICK_NSEC); | |
354879bb | 267 | */ |
3e51f33f | 268 | |
7b09cc5a PT |
269 | gtod = scd->tick_gtod + __gtod_offset; |
270 | clock = gtod + delta; | |
271 | min_clock = wrap_max(gtod, old_clock); | |
272 | max_clock = wrap_max(old_clock, gtod + TICK_NSEC); | |
3e51f33f | 273 | |
354879bb PZ |
274 | clock = wrap_max(clock, min_clock); |
275 | clock = wrap_min(clock, max_clock); | |
3e51f33f | 276 | |
152f9d07 | 277 | if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) |
def0a9b2 | 278 | goto again; |
56b90612 | 279 | |
def0a9b2 | 280 | return clock; |
3e51f33f PZ |
281 | } |
282 | ||
def0a9b2 | 283 | static u64 sched_clock_remote(struct sched_clock_data *scd) |
3e51f33f | 284 | { |
def0a9b2 PZ |
285 | struct sched_clock_data *my_scd = this_scd(); |
286 | u64 this_clock, remote_clock; | |
287 | u64 *ptr, old_val, val; | |
288 | ||
a1cbcaa9 TG |
289 | #if BITS_PER_LONG != 64 |
290 | again: | |
291 | /* | |
292 | * Careful here: The local and the remote clock values need to | |
293 | * be read out atomic as we need to compare the values and | |
294 | * then update either the local or the remote side. So the | |
295 | * cmpxchg64 below only protects one readout. | |
296 | * | |
297 | * We must reread via sched_clock_local() in the retry case on | |
298 | * 32bit as an NMI could use sched_clock_local() via the | |
299 | * tracer and hit between the readout of | |
300 | * the low32bit and the high 32bit portion. | |
301 | */ | |
302 | this_clock = sched_clock_local(my_scd); | |
303 | /* | |
304 | * We must enforce atomic readout on 32bit, otherwise the | |
305 | * update on the remote cpu can hit inbetween the readout of | |
306 | * the low32bit and the high 32bit portion. | |
307 | */ | |
308 | remote_clock = cmpxchg64(&scd->clock, 0, 0); | |
309 | #else | |
310 | /* | |
311 | * On 64bit the read of [my]scd->clock is atomic versus the | |
312 | * update, so we can avoid the above 32bit dance. | |
313 | */ | |
def0a9b2 PZ |
314 | sched_clock_local(my_scd); |
315 | again: | |
316 | this_clock = my_scd->clock; | |
317 | remote_clock = scd->clock; | |
a1cbcaa9 | 318 | #endif |
def0a9b2 PZ |
319 | |
320 | /* | |
321 | * Use the opportunity that we have both locks | |
322 | * taken to couple the two clocks: we take the | |
323 | * larger time as the latest time for both | |
324 | * runqueues. (this creates monotonic movement) | |
325 | */ | |
326 | if (likely((s64)(remote_clock - this_clock) < 0)) { | |
327 | ptr = &scd->clock; | |
328 | old_val = remote_clock; | |
329 | val = this_clock; | |
3e51f33f | 330 | } else { |
def0a9b2 PZ |
331 | /* |
332 | * Should be rare, but possible: | |
333 | */ | |
334 | ptr = &my_scd->clock; | |
335 | old_val = this_clock; | |
336 | val = remote_clock; | |
3e51f33f | 337 | } |
def0a9b2 | 338 | |
152f9d07 | 339 | if (cmpxchg64(ptr, old_val, val) != old_val) |
def0a9b2 PZ |
340 | goto again; |
341 | ||
342 | return val; | |
3e51f33f PZ |
343 | } |
344 | ||
c676329a PZ |
345 | /* |
346 | * Similar to cpu_clock(), but requires local IRQs to be disabled. | |
347 | * | |
348 | * See cpu_clock(). | |
349 | */ | |
3e51f33f PZ |
350 | u64 sched_clock_cpu(int cpu) |
351 | { | |
b342501c | 352 | struct sched_clock_data *scd; |
def0a9b2 PZ |
353 | u64 clock; |
354 | ||
35af99e6 | 355 | if (sched_clock_stable()) |
698eff63 | 356 | return sched_clock() + __sched_clock_offset; |
a381759d | 357 | |
a381759d PZ |
358 | if (unlikely(!sched_clock_running)) |
359 | return 0ull; | |
360 | ||
96b3d28b | 361 | preempt_disable_notrace(); |
def0a9b2 | 362 | scd = cpu_sdc(cpu); |
3e51f33f | 363 | |
def0a9b2 PZ |
364 | if (cpu != smp_processor_id()) |
365 | clock = sched_clock_remote(scd); | |
366 | else | |
367 | clock = sched_clock_local(scd); | |
96b3d28b | 368 | preempt_enable_notrace(); |
e4e4e534 | 369 | |
3e51f33f PZ |
370 | return clock; |
371 | } | |
2c923e94 | 372 | EXPORT_SYMBOL_GPL(sched_clock_cpu); |
3e51f33f PZ |
373 | |
374 | void sched_clock_tick(void) | |
375 | { | |
8325d9c0 | 376 | struct sched_clock_data *scd; |
a381759d | 377 | |
b421b22b PZ |
378 | if (sched_clock_stable()) |
379 | return; | |
380 | ||
381 | if (unlikely(!sched_clock_running)) | |
382 | return; | |
383 | ||
3e51f33f PZ |
384 | WARN_ON_ONCE(!irqs_disabled()); |
385 | ||
8325d9c0 | 386 | scd = this_scd(); |
cf15ca8d | 387 | __scd_stamp(scd); |
b421b22b PZ |
388 | sched_clock_local(scd); |
389 | } | |
390 | ||
391 | void sched_clock_tick_stable(void) | |
392 | { | |
393 | u64 gtod, clock; | |
3e51f33f | 394 | |
b421b22b PZ |
395 | if (!sched_clock_stable()) |
396 | return; | |
397 | ||
398 | /* | |
399 | * Called under watchdog_lock. | |
400 | * | |
401 | * The watchdog just found this TSC to (still) be stable, so now is a | |
402 | * good moment to update our __gtod_offset. Because once we find the | |
403 | * TSC to be unstable, any computation will be computing crap. | |
404 | */ | |
405 | local_irq_disable(); | |
406 | gtod = ktime_get_ns(); | |
407 | clock = sched_clock(); | |
408 | __gtod_offset = (clock + __sched_clock_offset) - gtod; | |
409 | local_irq_enable(); | |
3e51f33f PZ |
410 | } |
411 | ||
412 | /* | |
413 | * We are going deep-idle (irqs are disabled): | |
414 | */ | |
415 | void sched_clock_idle_sleep_event(void) | |
416 | { | |
417 | sched_clock_cpu(smp_processor_id()); | |
418 | } | |
419 | EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); | |
420 | ||
421 | /* | |
f9fccdb9 | 422 | * We just idled; resync with ktime. |
3e51f33f | 423 | */ |
ac1e843f | 424 | void sched_clock_idle_wakeup_event(void) |
3e51f33f | 425 | { |
f9fccdb9 PZ |
426 | unsigned long flags; |
427 | ||
428 | if (sched_clock_stable()) | |
429 | return; | |
430 | ||
431 | if (unlikely(timekeeping_suspended)) | |
1c5745aa TG |
432 | return; |
433 | ||
f9fccdb9 | 434 | local_irq_save(flags); |
354879bb | 435 | sched_clock_tick(); |
f9fccdb9 | 436 | local_irq_restore(flags); |
3e51f33f PZ |
437 | } |
438 | EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); | |
439 | ||
8325d9c0 PZ |
440 | #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
441 | ||
8325d9c0 PZ |
442 | u64 sched_clock_cpu(int cpu) |
443 | { | |
444 | if (unlikely(!sched_clock_running)) | |
445 | return 0; | |
446 | ||
447 | return sched_clock(); | |
448 | } | |
9881b024 | 449 | |
b9f8fcd5 | 450 | #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
76a2a6ee | 451 | |
545a2bf7 CB |
452 | /* |
453 | * Running clock - returns the time that has elapsed while a guest has been | |
454 | * running. | |
455 | * On a guest this value should be local_clock minus the time the guest was | |
456 | * suspended by the hypervisor (for any reason). | |
457 | * On bare metal this function should return the same as local_clock. | |
458 | * Architectures and sub-architectures can override this. | |
459 | */ | |
460 | u64 __weak running_clock(void) | |
461 | { | |
462 | return local_clock(); | |
463 | } |