Commit | Line | Data |
---|---|---|
3e51f33f | 1 | /* |
97fb7a0a | 2 | * sched_clock() for unstable CPU clocks |
3e51f33f | 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 | 13 | * |
97fb7a0a | 14 | * What this file implements: |
c676329a PZ |
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. | |
97fb7a0a | 29 | * local_clock() -- is cpu_clock() on the current CPU. |
c676329a | 30 | * |
ef08f0ff PZ |
31 | * sched_clock_cpu(i) |
32 | * | |
97fb7a0a | 33 | * How it is implemented: |
c676329a PZ |
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 | */ |
325ea10c | 55 | #include "sched.h" |
3e51f33f | 56 | |
2c3d103b HD |
57 | /* |
58 | * Scheduler clock - returns current time in nanosec units. | |
59 | * This is default implementation. | |
60 | * Architectures and sub-architectures can override this. | |
61 | */ | |
52f5684c | 62 | unsigned long long __weak sched_clock(void) |
2c3d103b | 63 | { |
92d23f70 R |
64 | return (unsigned long long)(jiffies - INITIAL_JIFFIES) |
65 | * (NSEC_PER_SEC / HZ); | |
2c3d103b | 66 | } |
b6ac23af | 67 | EXPORT_SYMBOL_GPL(sched_clock); |
3e51f33f | 68 | |
5bb6b1ea | 69 | __read_mostly int sched_clock_running; |
c1955a3d | 70 | |
9881b024 PZ |
71 | void sched_clock_init(void) |
72 | { | |
73 | sched_clock_running = 1; | |
74 | } | |
75 | ||
3e51f33f | 76 | #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK |
acb04058 PZ |
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 | */ | |
555570d7 | 84 | static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable); |
acb04058 | 85 | static int __sched_clock_stable_early = 1; |
35af99e6 | 86 | |
5680d809 | 87 | /* |
698eff63 | 88 | * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset |
5680d809 | 89 | */ |
698eff63 PZ |
90 | __read_mostly u64 __sched_clock_offset; |
91 | static __read_mostly u64 __gtod_offset; | |
5680d809 PZ |
92 | |
93 | struct sched_clock_data { | |
94 | u64 tick_raw; | |
95 | u64 tick_gtod; | |
96 | u64 clock; | |
97 | }; | |
98 | ||
99 | static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); | |
100 | ||
101 | static inline struct sched_clock_data *this_scd(void) | |
102 | { | |
103 | return this_cpu_ptr(&sched_clock_data); | |
104 | } | |
105 | ||
106 | static inline struct sched_clock_data *cpu_sdc(int cpu) | |
107 | { | |
108 | return &per_cpu(sched_clock_data, cpu); | |
109 | } | |
110 | ||
35af99e6 PZ |
111 | int sched_clock_stable(void) |
112 | { | |
555570d7 | 113 | return static_branch_likely(&__sched_clock_stable); |
35af99e6 PZ |
114 | } |
115 | ||
cf15ca8d PZ |
116 | static void __scd_stamp(struct sched_clock_data *scd) |
117 | { | |
118 | scd->tick_gtod = ktime_get_ns(); | |
119 | scd->tick_raw = sched_clock(); | |
120 | } | |
121 | ||
d375b4e0 | 122 | static void __set_sched_clock_stable(void) |
35af99e6 | 123 | { |
45aea321 | 124 | struct sched_clock_data *scd; |
5680d809 | 125 | |
45aea321 PZ |
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(); | |
5680d809 PZ |
132 | /* |
133 | * Attempt to make the (initial) unstable->stable transition continuous. | |
134 | */ | |
698eff63 | 135 | __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw); |
45aea321 | 136 | local_irq_enable(); |
5680d809 PZ |
137 | |
138 | printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n", | |
698eff63 PZ |
139 | scd->tick_gtod, __gtod_offset, |
140 | scd->tick_raw, __sched_clock_offset); | |
5680d809 | 141 | |
555570d7 | 142 | static_branch_enable(&__sched_clock_stable); |
4f49b90a | 143 | tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE); |
d375b4e0 PZ |
144 | } |
145 | ||
cf15ca8d PZ |
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 | */ | |
71fdb70e PZ |
157 | static void __sched_clock_work(struct work_struct *work) |
158 | { | |
cf15ca8d PZ |
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 | ||
7708d5f0 | 173 | printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n"); |
cf15ca8d PZ |
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 | ||
71fdb70e PZ |
178 | static_branch_disable(&__sched_clock_stable); |
179 | } | |
180 | ||
181 | static DECLARE_WORK(sched_clock_work, __sched_clock_work); | |
182 | ||
183 | static void __clear_sched_clock_stable(void) | |
35af99e6 | 184 | { |
cf15ca8d PZ |
185 | if (!sched_clock_stable()) |
186 | return; | |
5680d809 | 187 | |
4f49b90a | 188 | tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE); |
cf15ca8d | 189 | schedule_work(&sched_clock_work); |
71fdb70e | 190 | } |
6577e42a PZ |
191 | |
192 | void clear_sched_clock_stable(void) | |
193 | { | |
d375b4e0 PZ |
194 | __sched_clock_stable_early = 0; |
195 | ||
9881b024 | 196 | smp_mb(); /* matches sched_clock_init_late() */ |
d375b4e0 | 197 | |
9881b024 | 198 | if (sched_clock_running == 2) |
71fdb70e | 199 | __clear_sched_clock_stable(); |
6577e42a PZ |
200 | } |
201 | ||
2e44b7dd PZ |
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 | */ | |
206 | static int __init sched_clock_init_late(void) | |
3e51f33f | 207 | { |
9881b024 | 208 | sched_clock_running = 2; |
d375b4e0 PZ |
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(); | |
2e44b7dd PZ |
220 | |
221 | return 0; | |
3e51f33f | 222 | } |
2e44b7dd | 223 | late_initcall(sched_clock_init_late); |
3e51f33f | 224 | |
354879bb | 225 | /* |
b342501c | 226 | * min, max except they take wrapping into account |
354879bb PZ |
227 | */ |
228 | ||
229 | static inline u64 wrap_min(u64 x, u64 y) | |
230 | { | |
231 | return (s64)(x - y) < 0 ? x : y; | |
232 | } | |
233 | ||
234 | static inline u64 wrap_max(u64 x, u64 y) | |
235 | { | |
236 | return (s64)(x - y) > 0 ? x : y; | |
237 | } | |
238 | ||
3e51f33f PZ |
239 | /* |
240 | * update the percpu scd from the raw @now value | |
241 | * | |
242 | * - filter out backward motion | |
354879bb | 243 | * - use the GTOD tick value to create a window to filter crazy TSC values |
3e51f33f | 244 | */ |
def0a9b2 | 245 | static u64 sched_clock_local(struct sched_clock_data *scd) |
3e51f33f | 246 | { |
7b09cc5a | 247 | u64 now, clock, old_clock, min_clock, max_clock, gtod; |
def0a9b2 | 248 | s64 delta; |
3e51f33f | 249 | |
def0a9b2 PZ |
250 | again: |
251 | now = sched_clock(); | |
252 | delta = now - scd->tick_raw; | |
354879bb PZ |
253 | if (unlikely(delta < 0)) |
254 | delta = 0; | |
3e51f33f | 255 | |
def0a9b2 PZ |
256 | old_clock = scd->clock; |
257 | ||
354879bb PZ |
258 | /* |
259 | * scd->clock = clamp(scd->tick_gtod + delta, | |
b342501c IM |
260 | * max(scd->tick_gtod, scd->clock), |
261 | * scd->tick_gtod + TICK_NSEC); | |
354879bb | 262 | */ |
3e51f33f | 263 | |
7b09cc5a PT |
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); | |
3e51f33f | 268 | |
354879bb PZ |
269 | clock = wrap_max(clock, min_clock); |
270 | clock = wrap_min(clock, max_clock); | |
3e51f33f | 271 | |
152f9d07 | 272 | if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) |
def0a9b2 | 273 | goto again; |
56b90612 | 274 | |
def0a9b2 | 275 | return clock; |
3e51f33f PZ |
276 | } |
277 | ||
def0a9b2 | 278 | static u64 sched_clock_remote(struct sched_clock_data *scd) |
3e51f33f | 279 | { |
def0a9b2 PZ |
280 | struct sched_clock_data *my_scd = this_scd(); |
281 | u64 this_clock, remote_clock; | |
282 | u64 *ptr, old_val, val; | |
283 | ||
a1cbcaa9 TG |
284 | #if BITS_PER_LONG != 64 |
285 | again: | |
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 | |
97fb7a0a | 293 | * 32-bit kernels as an NMI could use sched_clock_local() via the |
a1cbcaa9 | 294 | * tracer and hit between the readout of |
97fb7a0a | 295 | * the low 32-bit and the high 32-bit portion. |
a1cbcaa9 TG |
296 | */ |
297 | this_clock = sched_clock_local(my_scd); | |
298 | /* | |
97fb7a0a IM |
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. | |
a1cbcaa9 TG |
302 | */ |
303 | remote_clock = cmpxchg64(&scd->clock, 0, 0); | |
304 | #else | |
305 | /* | |
97fb7a0a IM |
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. | |
a1cbcaa9 | 308 | */ |
def0a9b2 PZ |
309 | sched_clock_local(my_scd); |
310 | again: | |
311 | this_clock = my_scd->clock; | |
312 | remote_clock = scd->clock; | |
a1cbcaa9 | 313 | #endif |
def0a9b2 PZ |
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; | |
3e51f33f | 325 | } else { |
def0a9b2 PZ |
326 | /* |
327 | * Should be rare, but possible: | |
328 | */ | |
329 | ptr = &my_scd->clock; | |
330 | old_val = this_clock; | |
331 | val = remote_clock; | |
3e51f33f | 332 | } |
def0a9b2 | 333 | |
152f9d07 | 334 | if (cmpxchg64(ptr, old_val, val) != old_val) |
def0a9b2 PZ |
335 | goto again; |
336 | ||
337 | return val; | |
3e51f33f PZ |
338 | } |
339 | ||
c676329a PZ |
340 | /* |
341 | * Similar to cpu_clock(), but requires local IRQs to be disabled. | |
342 | * | |
343 | * See cpu_clock(). | |
344 | */ | |
3e51f33f PZ |
345 | u64 sched_clock_cpu(int cpu) |
346 | { | |
b342501c | 347 | struct sched_clock_data *scd; |
def0a9b2 PZ |
348 | u64 clock; |
349 | ||
35af99e6 | 350 | if (sched_clock_stable()) |
698eff63 | 351 | return sched_clock() + __sched_clock_offset; |
a381759d | 352 | |
a381759d PZ |
353 | if (unlikely(!sched_clock_running)) |
354 | return 0ull; | |
355 | ||
96b3d28b | 356 | preempt_disable_notrace(); |
def0a9b2 | 357 | scd = cpu_sdc(cpu); |
3e51f33f | 358 | |
def0a9b2 PZ |
359 | if (cpu != smp_processor_id()) |
360 | clock = sched_clock_remote(scd); | |
361 | else | |
362 | clock = sched_clock_local(scd); | |
96b3d28b | 363 | preempt_enable_notrace(); |
e4e4e534 | 364 | |
3e51f33f PZ |
365 | return clock; |
366 | } | |
2c923e94 | 367 | EXPORT_SYMBOL_GPL(sched_clock_cpu); |
3e51f33f PZ |
368 | |
369 | void sched_clock_tick(void) | |
370 | { | |
8325d9c0 | 371 | struct sched_clock_data *scd; |
a381759d | 372 | |
b421b22b PZ |
373 | if (sched_clock_stable()) |
374 | return; | |
375 | ||
376 | if (unlikely(!sched_clock_running)) | |
377 | return; | |
378 | ||
2c11dba0 | 379 | lockdep_assert_irqs_disabled(); |
3e51f33f | 380 | |
8325d9c0 | 381 | scd = this_scd(); |
cf15ca8d | 382 | __scd_stamp(scd); |
b421b22b PZ |
383 | sched_clock_local(scd); |
384 | } | |
385 | ||
386 | void sched_clock_tick_stable(void) | |
387 | { | |
388 | u64 gtod, clock; | |
3e51f33f | 389 | |
b421b22b PZ |
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(); | |
3e51f33f PZ |
405 | } |
406 | ||
407 | /* | |
408 | * We are going deep-idle (irqs are disabled): | |
409 | */ | |
410 | void sched_clock_idle_sleep_event(void) | |
411 | { | |
412 | sched_clock_cpu(smp_processor_id()); | |
413 | } | |
414 | EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); | |
415 | ||
416 | /* | |
f9fccdb9 | 417 | * We just idled; resync with ktime. |
3e51f33f | 418 | */ |
ac1e843f | 419 | void sched_clock_idle_wakeup_event(void) |
3e51f33f | 420 | { |
f9fccdb9 PZ |
421 | unsigned long flags; |
422 | ||
423 | if (sched_clock_stable()) | |
424 | return; | |
425 | ||
426 | if (unlikely(timekeeping_suspended)) | |
1c5745aa TG |
427 | return; |
428 | ||
f9fccdb9 | 429 | local_irq_save(flags); |
354879bb | 430 | sched_clock_tick(); |
f9fccdb9 | 431 | local_irq_restore(flags); |
3e51f33f PZ |
432 | } |
433 | EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); | |
434 | ||
8325d9c0 PZ |
435 | #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
436 | ||
8325d9c0 PZ |
437 | u64 sched_clock_cpu(int cpu) |
438 | { | |
439 | if (unlikely(!sched_clock_running)) | |
440 | return 0; | |
441 | ||
442 | return sched_clock(); | |
443 | } | |
9881b024 | 444 | |
b9f8fcd5 | 445 | #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
76a2a6ee | 446 | |
545a2bf7 CB |
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 | */ | |
455 | u64 __weak running_clock(void) | |
456 | { | |
457 | return local_clock(); | |
458 | } |