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Ingo Molnar14131f22009-02-26 18:47:11 +01001/*
2 * tracing clocks
3 *
4 * Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
5 *
6 * Implements 3 trace clock variants, with differing scalability/precision
7 * tradeoffs:
8 *
9 * - local: CPU-local trace clock
10 * - medium: scalable global clock with some jitter
11 * - global: globally monotonic, serialized clock
12 *
13 * Tracer plugins will chose a default from these clocks.
14 */
15#include <linux/spinlock.h>
Frederic Weisbeckerae1f3032010-02-28 19:42:38 +010016#include <linux/irqflags.h>
Ingo Molnar14131f22009-02-26 18:47:11 +010017#include <linux/hardirq.h>
18#include <linux/module.h>
19#include <linux/percpu.h>
20#include <linux/sched.h>
21#include <linux/ktime.h>
Dmitri Vorobievb8b94262009-03-22 19:11:11 +020022#include <linux/trace_clock.h>
Ingo Molnar14131f22009-02-26 18:47:11 +010023
24/*
25 * trace_clock_local(): the simplest and least coherent tracing clock.
26 *
27 * Useful for tracing that does not cross to other CPUs nor
28 * does it go through idle events.
29 */
30u64 notrace trace_clock_local(void)
31{
Peter Zijlstra6cc3c6e2009-03-10 19:03:43 +010032 u64 clock;
33
Ingo Molnar14131f22009-02-26 18:47:11 +010034 /*
35 * sched_clock() is an architecture implemented, fast, scalable,
36 * lockless clock. It is not guaranteed to be coherent across
37 * CPUs, nor across CPU idle events.
38 */
Steven Rostedt5168ae52010-06-03 09:36:50 -040039 preempt_disable_notrace();
Peter Zijlstra6cc3c6e2009-03-10 19:03:43 +010040 clock = sched_clock();
Steven Rostedt5168ae52010-06-03 09:36:50 -040041 preempt_enable_notrace();
Peter Zijlstra6cc3c6e2009-03-10 19:03:43 +010042
43 return clock;
Ingo Molnar14131f22009-02-26 18:47:11 +010044}
Paul E. McKenneydc975e92012-11-15 11:27:26 -080045EXPORT_SYMBOL_GPL(trace_clock_local);
Ingo Molnar14131f22009-02-26 18:47:11 +010046
47/*
Lucas De Marchi25985ed2011-03-30 22:57:33 -030048 * trace_clock(): 'between' trace clock. Not completely serialized,
Ingo Molnar14131f22009-02-26 18:47:11 +010049 * but not completely incorrect when crossing CPUs either.
50 *
51 * This is based on cpu_clock(), which will allow at most ~1 jiffy of
52 * jitter between CPUs. So it's a pretty scalable clock, but there
53 * can be offsets in the trace data.
54 */
55u64 notrace trace_clock(void)
56{
Peter Zijlstrac6763292010-05-25 10:48:51 +020057 return local_clock();
Ingo Molnar14131f22009-02-26 18:47:11 +010058}
59
Steven Rostedt (Red Hat)8aacf012013-03-14 13:13:45 -040060/*
61 * trace_jiffy_clock(): Simply use jiffies as a clock counter.
62 */
63u64 notrace trace_clock_jiffies(void)
64{
65 u64 jiffy = jiffies - INITIAL_JIFFIES;
66
67 /* Return nsecs */
68 return (u64)jiffies_to_usecs(jiffy) * 1000ULL;
69}
Ingo Molnar14131f22009-02-26 18:47:11 +010070
71/*
72 * trace_clock_global(): special globally coherent trace clock
73 *
74 * It has higher overhead than the other trace clocks but is still
75 * an order of magnitude faster than GTOD derived hardware clocks.
76 *
77 * Used by plugins that need globally coherent timestamps.
78 */
79
Steven Rostedt6ca6cca2009-09-15 12:24:22 -040080/* keep prev_time and lock in the same cacheline. */
81static struct {
82 u64 prev_time;
Thomas Gleixner445c8952009-12-02 19:49:50 +010083 arch_spinlock_t lock;
Steven Rostedt6ca6cca2009-09-15 12:24:22 -040084} trace_clock_struct ____cacheline_aligned_in_smp =
85 {
Thomas Gleixneredc35bd2009-12-03 12:38:57 +010086 .lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
Steven Rostedt6ca6cca2009-09-15 12:24:22 -040087 };
Ingo Molnar14131f22009-02-26 18:47:11 +010088
89u64 notrace trace_clock_global(void)
90{
91 unsigned long flags;
92 int this_cpu;
93 u64 now;
94
Li Zefane36673e2010-03-24 10:57:37 +080095 local_irq_save(flags);
Ingo Molnar14131f22009-02-26 18:47:11 +010096
97 this_cpu = raw_smp_processor_id();
Namhyung Kim5e67b512012-12-27 11:49:45 +090098 now = sched_clock_cpu(this_cpu);
Ingo Molnar14131f22009-02-26 18:47:11 +010099 /*
100 * If in an NMI context then dont risk lockups and return the
101 * cpu_clock() time:
102 */
103 if (unlikely(in_nmi()))
104 goto out;
105
Thomas Gleixner0199c4e2009-12-02 20:01:25 +0100106 arch_spin_lock(&trace_clock_struct.lock);
Ingo Molnar14131f22009-02-26 18:47:11 +0100107
108 /*
109 * TODO: if this happens often then maybe we should reset
Steven Rostedt6ca6cca2009-09-15 12:24:22 -0400110 * my_scd->clock to prev_time+1, to make sure
Ingo Molnar14131f22009-02-26 18:47:11 +0100111 * we start ticking with the local clock from now on?
112 */
Steven Rostedt6ca6cca2009-09-15 12:24:22 -0400113 if ((s64)(now - trace_clock_struct.prev_time) < 0)
114 now = trace_clock_struct.prev_time + 1;
Ingo Molnar14131f22009-02-26 18:47:11 +0100115
Steven Rostedt6ca6cca2009-09-15 12:24:22 -0400116 trace_clock_struct.prev_time = now;
Ingo Molnar14131f22009-02-26 18:47:11 +0100117
Thomas Gleixner0199c4e2009-12-02 20:01:25 +0100118 arch_spin_unlock(&trace_clock_struct.lock);
Ingo Molnar14131f22009-02-26 18:47:11 +0100119
120 out:
Li Zefane36673e2010-03-24 10:57:37 +0800121 local_irq_restore(flags);
Ingo Molnar14131f22009-02-26 18:47:11 +0100122
123 return now;
124}
Steven Rostedt62496872011-09-19 11:35:58 -0400125
126static atomic64_t trace_counter;
127
128/*
129 * trace_clock_counter(): simply an atomic counter.
130 * Use the trace_counter "counter" for cases where you do not care
131 * about timings, but are interested in strict ordering.
132 */
133u64 notrace trace_clock_counter(void)
134{
135 return atomic64_add_return(1, &trace_counter);
136}