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Peter Zijlstra3e51f332008-05-03 18:29:28 +02001/*
2 * sched_clock for unstable cpu clocks
3 *
4 * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
5 *
Steven Rostedtc300ba22008-07-09 00:15:33 -04006 * Updates and enhancements:
7 * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
8 *
Peter Zijlstra3e51f332008-05-03 18:29:28 +02009 * Based on code by:
10 * Ingo Molnar <mingo@redhat.com>
11 * Guillaume Chazarain <guichaz@gmail.com>
12 *
Peter Zijlstrac6763292010-05-25 10:48:51 +020013 *
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)
Peter Zijlstra3e51f332008-05-03 18:29:28 +020043 * - sched_clock()
44 * - explicit idle events
45 *
Peter Zijlstrac6763292010-05-25 10:48:51 +020046 * 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.
Peter Zijlstra3e51f332008-05-03 18:29:28 +020049 *
50 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
51 * that is otherwise invisible (TSC gets stopped).
52 *
Peter Zijlstrac6763292010-05-25 10:48:51 +020053 *
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().
Peter Zijlstra3e51f332008-05-03 18:29:28 +020062 */
Peter Zijlstra3e51f332008-05-03 18:29:28 +020063#include <linux/spinlock.h>
Ingo Molnar6409c4d2008-05-12 21:21:14 +020064#include <linux/hardirq.h>
Peter Zijlstra3e51f332008-05-03 18:29:28 +020065#include <linux/module.h>
Ingo Molnarb3425012009-02-26 20:20:29 +010066#include <linux/percpu.h>
67#include <linux/ktime.h>
68#include <linux/sched.h>
Peter Zijlstra3e51f332008-05-03 18:29:28 +020069
Hugh Dickins2c3d1032008-07-25 19:45:00 +010070/*
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{
Ron92d23f72009-05-08 22:54:49 +093077 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
78 * (NSEC_PER_SEC / HZ);
Hugh Dickins2c3d1032008-07-25 19:45:00 +010079}
Divyesh Shahb6ac23af2010-04-15 08:54:59 +020080EXPORT_SYMBOL_GPL(sched_clock);
Peter Zijlstra3e51f332008-05-03 18:29:28 +020081
Peter Zijlstra5bb6b1e2010-11-19 21:11:09 +010082__read_mostly int sched_clock_running;
Peter Zijlstrac1955a32008-08-11 08:59:03 +020083
Peter Zijlstra3e51f332008-05-03 18:29:28 +020084#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
Ingo Molnarb3425012009-02-26 20:20:29 +010085__read_mostly int sched_clock_stable;
Peter Zijlstra3e51f332008-05-03 18:29:28 +020086
87struct sched_clock_data {
Peter Zijlstra3e51f332008-05-03 18:29:28 +020088 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());
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200108 int cpu;
109
110 for_each_possible_cpu(cpu) {
111 struct sched_clock_data *scd = cpu_sdc(cpu);
112
Peter Zijlstraa3817592008-05-29 10:07:15 +0200113 scd->tick_raw = 0;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200114 scd->tick_gtod = ktime_now;
115 scd->clock = ktime_now;
116 }
Peter Zijlstraa3817592008-05-29 10:07:15 +0200117
118 sched_clock_running = 1;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200119}
120
121/*
Ingo Molnarb3425012009-02-26 20:20:29 +0100122 * min, max except they take wrapping into account
Peter Zijlstra354879b2008-08-25 17:15:34 +0200123 */
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/*
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200136 * update the percpu scd from the raw @now value
137 *
138 * - filter out backward motion
Peter Zijlstra354879b2008-08-25 17:15:34 +0200139 * - use the GTOD tick value to create a window to filter crazy TSC values
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200140 */
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200141static u64 sched_clock_local(struct sched_clock_data *scd)
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200142{
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200143 u64 now, clock, old_clock, min_clock, max_clock;
144 s64 delta;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200145
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200146again:
147 now = sched_clock();
148 delta = now - scd->tick_raw;
Peter Zijlstra354879b2008-08-25 17:15:34 +0200149 if (unlikely(delta < 0))
150 delta = 0;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200151
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200152 old_clock = scd->clock;
153
Peter Zijlstra354879b2008-08-25 17:15:34 +0200154 /*
155 * scd->clock = clamp(scd->tick_gtod + delta,
Ingo Molnarb3425012009-02-26 20:20:29 +0100156 * max(scd->tick_gtod, scd->clock),
157 * scd->tick_gtod + TICK_NSEC);
Peter Zijlstra354879b2008-08-25 17:15:34 +0200158 */
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200159
Peter Zijlstra354879b2008-08-25 17:15:34 +0200160 clock = scd->tick_gtod + delta;
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200161 min_clock = wrap_max(scd->tick_gtod, old_clock);
162 max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200163
Peter Zijlstra354879b2008-08-25 17:15:34 +0200164 clock = wrap_max(clock, min_clock);
165 clock = wrap_min(clock, max_clock);
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200166
Eric Dumazet152f9d02009-09-30 20:36:19 +0200167 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200168 goto again;
Ingo Molnar56b90612008-07-30 10:15:55 +0200169
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200170 return clock;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200171}
172
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200173static u64 sched_clock_remote(struct sched_clock_data *scd)
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200174{
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200175 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;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200194 } else {
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200195 /*
196 * Should be rare, but possible:
197 */
198 ptr = &my_scd->clock;
199 old_val = this_clock;
200 val = remote_clock;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200201 }
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200202
Eric Dumazet152f9d02009-09-30 20:36:19 +0200203 if (cmpxchg64(ptr, old_val, val) != old_val)
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200204 goto again;
205
206 return val;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200207}
208
Peter Zijlstrac6763292010-05-25 10:48:51 +0200209/*
210 * Similar to cpu_clock(), but requires local IRQs to be disabled.
211 *
212 * See cpu_clock().
213 */
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200214u64 sched_clock_cpu(int cpu)
215{
Ingo Molnarb3425012009-02-26 20:20:29 +0100216 struct sched_clock_data *scd;
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200217 u64 clock;
218
219 WARN_ON_ONCE(!irqs_disabled());
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200220
Ingo Molnarb3425012009-02-26 20:20:29 +0100221 if (sched_clock_stable)
222 return sched_clock();
Peter Zijlstraa3817592008-05-29 10:07:15 +0200223
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200224 if (unlikely(!sched_clock_running))
225 return 0ull;
226
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200227 scd = cpu_sdc(cpu);
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200228
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200229 if (cpu != smp_processor_id())
230 clock = sched_clock_remote(scd);
231 else
232 clock = sched_clock_local(scd);
Ingo Molnare4e4e532008-04-14 08:50:02 +0200233
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200234 return clock;
235}
236
237void sched_clock_tick(void)
238{
Peter Zijlstra8325d9c2009-02-26 21:40:16 +0100239 struct sched_clock_data *scd;
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200240 u64 now, now_gtod;
241
Peter Zijlstra8325d9c2009-02-26 21:40:16 +0100242 if (sched_clock_stable)
243 return;
244
Peter Zijlstraa3817592008-05-29 10:07:15 +0200245 if (unlikely(!sched_clock_running))
246 return;
247
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200248 WARN_ON_ONCE(!irqs_disabled());
249
Peter Zijlstra8325d9c2009-02-26 21:40:16 +0100250 scd = this_scd();
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200251 now_gtod = ktime_to_ns(ktime_get());
Steven Rostedta83bc472008-07-09 00:15:32 -0400252 now = sched_clock();
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200253
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200254 scd->tick_raw = now;
255 scd->tick_gtod = now_gtod;
Peter Zijlstradef0a9b2009-09-18 20:14:01 +0200256 sched_clock_local(scd);
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200257}
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{
Thomas Gleixner1c5745a2008-12-22 23:05:28 +0100273 if (timekeeping_suspended)
274 return;
275
Peter Zijlstra354879b2008-08-25 17:15:34 +0200276 sched_clock_tick();
Peter Zijlstra3e51f332008-05-03 18:29:28 +0200277 touch_softlockup_watchdog();
278}
279EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
280
Peter Zijlstrac6763292010-05-25 10:48:51 +0200281/*
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)
David Millerb9f8fcd2009-12-13 18:25:02 -0800292{
Peter Zijlstrac6763292010-05-25 10:48:51 +0200293 u64 clock;
David Millerb9f8fcd2009-12-13 18:25:02 -0800294 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
Peter Zijlstrac6763292010-05-25 10:48:51 +0200303/*
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
Peter Zijlstra8325d9c2009-02-26 21:40:16 +0100322#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
Peter Zijlstrac6763292010-05-25 10:48:51 +0200337u64 cpu_clock(int cpu)
Peter Zijlstra76a2a6e2008-06-27 13:41:15 +0200338{
David Millerb9f8fcd2009-12-13 18:25:02 -0800339 return sched_clock_cpu(cpu);
Peter Zijlstra76a2a6e2008-06-27 13:41:15 +0200340}
David Millerb9f8fcd2009-12-13 18:25:02 -0800341
Peter Zijlstrac6763292010-05-25 10:48:51 +0200342u64 local_clock(void)
343{
344 return sched_clock_cpu(0);
345}
346
David Millerb9f8fcd2009-12-13 18:25:02 -0800347#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
348
Ingo Molnar4c9fe8a2008-06-27 14:49:35 +0200349EXPORT_SYMBOL_GPL(cpu_clock);
Peter Zijlstrac6763292010-05-25 10:48:51 +0200350EXPORT_SYMBOL_GPL(local_clock);