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3e51f33f PZ |
1 | /* |
2 | * sched_clock for unstable cpu clocks | |
3 | * | |
4 | * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> | |
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. | |
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) | |
3e51f33f PZ |
43 | * - sched_clock() |
44 | * - explicit idle events | |
45 | * | |
c676329a PZ |
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. | |
3e51f33f PZ |
49 | * |
50 | * Furthermore, explicit sleep and wakeup hooks allow us to account for time | |
51 | * that is otherwise invisible (TSC gets stopped). | |
52 | * | |
c676329a PZ |
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(). | |
3e51f33f | 62 | */ |
3e51f33f | 63 | #include <linux/spinlock.h> |
6409c4da | 64 | #include <linux/hardirq.h> |
9984de1a | 65 | #include <linux/export.h> |
b342501c IM |
66 | #include <linux/percpu.h> |
67 | #include <linux/ktime.h> | |
68 | #include <linux/sched.h> | |
3e51f33f | 69 | |
2c3d103b HD |
70 | /* |
71 | * Scheduler clock - returns current time in nanosec units. | |
72 | * This is default implementation. | |
73 | * Architectures and sub-architectures can override this. | |
74 | */ | |
75 | unsigned long long __attribute__((weak)) sched_clock(void) | |
76 | { | |
92d23f70 R |
77 | return (unsigned long long)(jiffies - INITIAL_JIFFIES) |
78 | * (NSEC_PER_SEC / HZ); | |
2c3d103b | 79 | } |
b6ac23af | 80 | EXPORT_SYMBOL_GPL(sched_clock); |
3e51f33f | 81 | |
5bb6b1ea | 82 | __read_mostly int sched_clock_running; |
c1955a3d | 83 | |
3e51f33f | 84 | #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK |
b342501c | 85 | __read_mostly int sched_clock_stable; |
3e51f33f PZ |
86 | |
87 | struct sched_clock_data { | |
3e51f33f PZ |
88 | u64 tick_raw; |
89 | u64 tick_gtod; | |
90 | u64 clock; | |
91 | }; | |
92 | ||
93 | static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); | |
94 | ||
95 | static inline struct sched_clock_data *this_scd(void) | |
96 | { | |
97 | return &__get_cpu_var(sched_clock_data); | |
98 | } | |
99 | ||
100 | static inline struct sched_clock_data *cpu_sdc(int cpu) | |
101 | { | |
102 | return &per_cpu(sched_clock_data, cpu); | |
103 | } | |
104 | ||
105 | void sched_clock_init(void) | |
106 | { | |
107 | u64 ktime_now = ktime_to_ns(ktime_get()); | |
3e51f33f PZ |
108 | int cpu; |
109 | ||
110 | for_each_possible_cpu(cpu) { | |
111 | struct sched_clock_data *scd = cpu_sdc(cpu); | |
112 | ||
a381759d | 113 | scd->tick_raw = 0; |
3e51f33f PZ |
114 | scd->tick_gtod = ktime_now; |
115 | scd->clock = ktime_now; | |
116 | } | |
a381759d PZ |
117 | |
118 | sched_clock_running = 1; | |
3e51f33f PZ |
119 | } |
120 | ||
354879bb | 121 | /* |
b342501c | 122 | * min, max except they take wrapping into account |
354879bb PZ |
123 | */ |
124 | ||
125 | static inline u64 wrap_min(u64 x, u64 y) | |
126 | { | |
127 | return (s64)(x - y) < 0 ? x : y; | |
128 | } | |
129 | ||
130 | static inline u64 wrap_max(u64 x, u64 y) | |
131 | { | |
132 | return (s64)(x - y) > 0 ? x : y; | |
133 | } | |
134 | ||
3e51f33f PZ |
135 | /* |
136 | * update the percpu scd from the raw @now value | |
137 | * | |
138 | * - filter out backward motion | |
354879bb | 139 | * - use the GTOD tick value to create a window to filter crazy TSC values |
3e51f33f | 140 | */ |
def0a9b2 | 141 | static u64 sched_clock_local(struct sched_clock_data *scd) |
3e51f33f | 142 | { |
def0a9b2 PZ |
143 | u64 now, clock, old_clock, min_clock, max_clock; |
144 | s64 delta; | |
3e51f33f | 145 | |
def0a9b2 PZ |
146 | again: |
147 | now = sched_clock(); | |
148 | delta = now - scd->tick_raw; | |
354879bb PZ |
149 | if (unlikely(delta < 0)) |
150 | delta = 0; | |
3e51f33f | 151 | |
def0a9b2 PZ |
152 | old_clock = scd->clock; |
153 | ||
354879bb PZ |
154 | /* |
155 | * scd->clock = clamp(scd->tick_gtod + delta, | |
b342501c IM |
156 | * max(scd->tick_gtod, scd->clock), |
157 | * scd->tick_gtod + TICK_NSEC); | |
354879bb | 158 | */ |
3e51f33f | 159 | |
354879bb | 160 | clock = scd->tick_gtod + delta; |
def0a9b2 PZ |
161 | min_clock = wrap_max(scd->tick_gtod, old_clock); |
162 | max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC); | |
3e51f33f | 163 | |
354879bb PZ |
164 | clock = wrap_max(clock, min_clock); |
165 | clock = wrap_min(clock, max_clock); | |
3e51f33f | 166 | |
152f9d07 | 167 | if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) |
def0a9b2 | 168 | goto again; |
56b90612 | 169 | |
def0a9b2 | 170 | return clock; |
3e51f33f PZ |
171 | } |
172 | ||
def0a9b2 | 173 | static u64 sched_clock_remote(struct sched_clock_data *scd) |
3e51f33f | 174 | { |
def0a9b2 PZ |
175 | struct sched_clock_data *my_scd = this_scd(); |
176 | u64 this_clock, remote_clock; | |
177 | u64 *ptr, old_val, val; | |
178 | ||
a1cbcaa9 TG |
179 | #if BITS_PER_LONG != 64 |
180 | again: | |
181 | /* | |
182 | * Careful here: The local and the remote clock values need to | |
183 | * be read out atomic as we need to compare the values and | |
184 | * then update either the local or the remote side. So the | |
185 | * cmpxchg64 below only protects one readout. | |
186 | * | |
187 | * We must reread via sched_clock_local() in the retry case on | |
188 | * 32bit as an NMI could use sched_clock_local() via the | |
189 | * tracer and hit between the readout of | |
190 | * the low32bit and the high 32bit portion. | |
191 | */ | |
192 | this_clock = sched_clock_local(my_scd); | |
193 | /* | |
194 | * We must enforce atomic readout on 32bit, otherwise the | |
195 | * update on the remote cpu can hit inbetween the readout of | |
196 | * the low32bit and the high 32bit portion. | |
197 | */ | |
198 | remote_clock = cmpxchg64(&scd->clock, 0, 0); | |
199 | #else | |
200 | /* | |
201 | * On 64bit the read of [my]scd->clock is atomic versus the | |
202 | * update, so we can avoid the above 32bit dance. | |
203 | */ | |
def0a9b2 PZ |
204 | sched_clock_local(my_scd); |
205 | again: | |
206 | this_clock = my_scd->clock; | |
207 | remote_clock = scd->clock; | |
a1cbcaa9 | 208 | #endif |
def0a9b2 PZ |
209 | |
210 | /* | |
211 | * Use the opportunity that we have both locks | |
212 | * taken to couple the two clocks: we take the | |
213 | * larger time as the latest time for both | |
214 | * runqueues. (this creates monotonic movement) | |
215 | */ | |
216 | if (likely((s64)(remote_clock - this_clock) < 0)) { | |
217 | ptr = &scd->clock; | |
218 | old_val = remote_clock; | |
219 | val = this_clock; | |
3e51f33f | 220 | } else { |
def0a9b2 PZ |
221 | /* |
222 | * Should be rare, but possible: | |
223 | */ | |
224 | ptr = &my_scd->clock; | |
225 | old_val = this_clock; | |
226 | val = remote_clock; | |
3e51f33f | 227 | } |
def0a9b2 | 228 | |
152f9d07 | 229 | if (cmpxchg64(ptr, old_val, val) != old_val) |
def0a9b2 PZ |
230 | goto again; |
231 | ||
232 | return val; | |
3e51f33f PZ |
233 | } |
234 | ||
c676329a PZ |
235 | /* |
236 | * Similar to cpu_clock(), but requires local IRQs to be disabled. | |
237 | * | |
238 | * See cpu_clock(). | |
239 | */ | |
3e51f33f PZ |
240 | u64 sched_clock_cpu(int cpu) |
241 | { | |
b342501c | 242 | struct sched_clock_data *scd; |
def0a9b2 PZ |
243 | u64 clock; |
244 | ||
245 | WARN_ON_ONCE(!irqs_disabled()); | |
3e51f33f | 246 | |
b342501c IM |
247 | if (sched_clock_stable) |
248 | return sched_clock(); | |
a381759d | 249 | |
a381759d PZ |
250 | if (unlikely(!sched_clock_running)) |
251 | return 0ull; | |
252 | ||
def0a9b2 | 253 | scd = cpu_sdc(cpu); |
3e51f33f | 254 | |
def0a9b2 PZ |
255 | if (cpu != smp_processor_id()) |
256 | clock = sched_clock_remote(scd); | |
257 | else | |
258 | clock = sched_clock_local(scd); | |
e4e4e534 | 259 | |
3e51f33f PZ |
260 | return clock; |
261 | } | |
262 | ||
263 | void sched_clock_tick(void) | |
264 | { | |
8325d9c0 | 265 | struct sched_clock_data *scd; |
3e51f33f PZ |
266 | u64 now, now_gtod; |
267 | ||
8325d9c0 PZ |
268 | if (sched_clock_stable) |
269 | return; | |
270 | ||
a381759d PZ |
271 | if (unlikely(!sched_clock_running)) |
272 | return; | |
273 | ||
3e51f33f PZ |
274 | WARN_ON_ONCE(!irqs_disabled()); |
275 | ||
8325d9c0 | 276 | scd = this_scd(); |
3e51f33f | 277 | now_gtod = ktime_to_ns(ktime_get()); |
a83bc47c | 278 | now = sched_clock(); |
3e51f33f | 279 | |
3e51f33f PZ |
280 | scd->tick_raw = now; |
281 | scd->tick_gtod = now_gtod; | |
def0a9b2 | 282 | sched_clock_local(scd); |
3e51f33f PZ |
283 | } |
284 | ||
285 | /* | |
286 | * We are going deep-idle (irqs are disabled): | |
287 | */ | |
288 | void sched_clock_idle_sleep_event(void) | |
289 | { | |
290 | sched_clock_cpu(smp_processor_id()); | |
291 | } | |
292 | EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); | |
293 | ||
294 | /* | |
295 | * We just idled delta nanoseconds (called with irqs disabled): | |
296 | */ | |
297 | void sched_clock_idle_wakeup_event(u64 delta_ns) | |
298 | { | |
1c5745aa TG |
299 | if (timekeeping_suspended) |
300 | return; | |
301 | ||
354879bb | 302 | sched_clock_tick(); |
3e51f33f PZ |
303 | touch_softlockup_watchdog(); |
304 | } | |
305 | EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); | |
306 | ||
c676329a PZ |
307 | /* |
308 | * As outlined at the top, provides a fast, high resolution, nanosecond | |
309 | * time source that is monotonic per cpu argument and has bounded drift | |
310 | * between cpus. | |
311 | * | |
312 | * ######################### BIG FAT WARNING ########################## | |
313 | * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can # | |
314 | * # go backwards !! # | |
315 | * #################################################################### | |
316 | */ | |
317 | u64 cpu_clock(int cpu) | |
b9f8fcd5 | 318 | { |
c676329a | 319 | u64 clock; |
b9f8fcd5 DM |
320 | unsigned long flags; |
321 | ||
322 | local_irq_save(flags); | |
323 | clock = sched_clock_cpu(cpu); | |
324 | local_irq_restore(flags); | |
325 | ||
326 | return clock; | |
327 | } | |
328 | ||
c676329a PZ |
329 | /* |
330 | * Similar to cpu_clock() for the current cpu. Time will only be observed | |
331 | * to be monotonic if care is taken to only compare timestampt taken on the | |
332 | * same CPU. | |
333 | * | |
334 | * See cpu_clock(). | |
335 | */ | |
336 | u64 local_clock(void) | |
337 | { | |
338 | u64 clock; | |
339 | unsigned long flags; | |
340 | ||
341 | local_irq_save(flags); | |
342 | clock = sched_clock_cpu(smp_processor_id()); | |
343 | local_irq_restore(flags); | |
344 | ||
345 | return clock; | |
346 | } | |
347 | ||
8325d9c0 PZ |
348 | #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
349 | ||
350 | void sched_clock_init(void) | |
351 | { | |
352 | sched_clock_running = 1; | |
353 | } | |
354 | ||
355 | u64 sched_clock_cpu(int cpu) | |
356 | { | |
357 | if (unlikely(!sched_clock_running)) | |
358 | return 0; | |
359 | ||
360 | return sched_clock(); | |
361 | } | |
362 | ||
c676329a | 363 | u64 cpu_clock(int cpu) |
76a2a6ee | 364 | { |
b9f8fcd5 DM |
365 | return sched_clock_cpu(cpu); |
366 | } | |
76a2a6ee | 367 | |
c676329a PZ |
368 | u64 local_clock(void) |
369 | { | |
370 | return sched_clock_cpu(0); | |
371 | } | |
372 | ||
b9f8fcd5 | 373 | #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
76a2a6ee | 374 | |
4c9fe8ad | 375 | EXPORT_SYMBOL_GPL(cpu_clock); |
c676329a | 376 | EXPORT_SYMBOL_GPL(local_clock); |