Loading...
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}
1/*
2 * sched_clock for unstable cpu clocks
3 *
4 * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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:
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)
43 * - sched_clock()
44 * - explicit idle events
45 *
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.
49 *
50 * Furthermore, explicit sleep and wakeup hooks allow us to account for time
51 * that is otherwise invisible (TSC gets stopped).
52 *
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().
62 */
63#include <linux/spinlock.h>
64#include <linux/hardirq.h>
65#include <linux/export.h>
66#include <linux/percpu.h>
67#include <linux/ktime.h>
68#include <linux/sched.h>
69
70/*
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{
77 return (unsigned long long)(jiffies - INITIAL_JIFFIES)
78 * (NSEC_PER_SEC / HZ);
79}
80EXPORT_SYMBOL_GPL(sched_clock);
81
82__read_mostly int sched_clock_running;
83
84#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
85__read_mostly int sched_clock_stable;
86
87struct sched_clock_data {
88 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());
108 int cpu;
109
110 for_each_possible_cpu(cpu) {
111 struct sched_clock_data *scd = cpu_sdc(cpu);
112
113 scd->tick_raw = 0;
114 scd->tick_gtod = ktime_now;
115 scd->clock = ktime_now;
116 }
117
118 sched_clock_running = 1;
119}
120
121/*
122 * min, max except they take wrapping into account
123 */
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/*
136 * update the percpu scd from the raw @now value
137 *
138 * - filter out backward motion
139 * - use the GTOD tick value to create a window to filter crazy TSC values
140 */
141static u64 sched_clock_local(struct sched_clock_data *scd)
142{
143 u64 now, clock, old_clock, min_clock, max_clock;
144 s64 delta;
145
146again:
147 now = sched_clock();
148 delta = now - scd->tick_raw;
149 if (unlikely(delta < 0))
150 delta = 0;
151
152 old_clock = scd->clock;
153
154 /*
155 * scd->clock = clamp(scd->tick_gtod + delta,
156 * max(scd->tick_gtod, scd->clock),
157 * scd->tick_gtod + TICK_NSEC);
158 */
159
160 clock = scd->tick_gtod + delta;
161 min_clock = wrap_max(scd->tick_gtod, old_clock);
162 max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
163
164 clock = wrap_max(clock, min_clock);
165 clock = wrap_min(clock, max_clock);
166
167 if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
168 goto again;
169
170 return clock;
171}
172
173static u64 sched_clock_remote(struct sched_clock_data *scd)
174{
175 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;
194 } else {
195 /*
196 * Should be rare, but possible:
197 */
198 ptr = &my_scd->clock;
199 old_val = this_clock;
200 val = remote_clock;
201 }
202
203 if (cmpxchg64(ptr, old_val, val) != old_val)
204 goto again;
205
206 return val;
207}
208
209/*
210 * Similar to cpu_clock(), but requires local IRQs to be disabled.
211 *
212 * See cpu_clock().
213 */
214u64 sched_clock_cpu(int cpu)
215{
216 struct sched_clock_data *scd;
217 u64 clock;
218
219 WARN_ON_ONCE(!irqs_disabled());
220
221 if (sched_clock_stable)
222 return sched_clock();
223
224 if (unlikely(!sched_clock_running))
225 return 0ull;
226
227 scd = cpu_sdc(cpu);
228
229 if (cpu != smp_processor_id())
230 clock = sched_clock_remote(scd);
231 else
232 clock = sched_clock_local(scd);
233
234 return clock;
235}
236
237void sched_clock_tick(void)
238{
239 struct sched_clock_data *scd;
240 u64 now, now_gtod;
241
242 if (sched_clock_stable)
243 return;
244
245 if (unlikely(!sched_clock_running))
246 return;
247
248 WARN_ON_ONCE(!irqs_disabled());
249
250 scd = this_scd();
251 now_gtod = ktime_to_ns(ktime_get());
252 now = sched_clock();
253
254 scd->tick_raw = now;
255 scd->tick_gtod = now_gtod;
256 sched_clock_local(scd);
257}
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{
273 if (timekeeping_suspended)
274 return;
275
276 sched_clock_tick();
277 touch_softlockup_watchdog();
278}
279EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
280
281/*
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)
292{
293 u64 clock;
294 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
303/*
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
322#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
337u64 cpu_clock(int cpu)
338{
339 return sched_clock_cpu(cpu);
340}
341
342u64 local_clock(void)
343{
344 return sched_clock_cpu(0);
345}
346
347#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
348
349EXPORT_SYMBOL_GPL(cpu_clock);
350EXPORT_SYMBOL_GPL(local_clock);