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1/*
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>
16#include <linux/irqflags.h>
17#include <linux/hardirq.h>
18#include <linux/module.h>
19#include <linux/percpu.h>
20#include <linux/sched.h>
21#include <linux/sched/clock.h>
22#include <linux/ktime.h>
23#include <linux/trace_clock.h>
24
25/*
26 * trace_clock_local(): the simplest and least coherent tracing clock.
27 *
28 * Useful for tracing that does not cross to other CPUs nor
29 * does it go through idle events.
30 */
31u64 notrace trace_clock_local(void)
32{
33 u64 clock;
34
35 /*
36 * sched_clock() is an architecture implemented, fast, scalable,
37 * lockless clock. It is not guaranteed to be coherent across
38 * CPUs, nor across CPU idle events.
39 */
40 preempt_disable_notrace();
41 clock = sched_clock();
42 preempt_enable_notrace();
43
44 return clock;
45}
46EXPORT_SYMBOL_GPL(trace_clock_local);
47
48/*
49 * trace_clock(): 'between' trace clock. Not completely serialized,
50 * but not completely incorrect when crossing CPUs either.
51 *
52 * This is based on cpu_clock(), which will allow at most ~1 jiffy of
53 * jitter between CPUs. So it's a pretty scalable clock, but there
54 * can be offsets in the trace data.
55 */
56u64 notrace trace_clock(void)
57{
58 return local_clock();
59}
60EXPORT_SYMBOL_GPL(trace_clock);
61
62/*
63 * trace_jiffy_clock(): Simply use jiffies as a clock counter.
64 * Note that this use of jiffies_64 is not completely safe on
65 * 32-bit systems. But the window is tiny, and the effect if
66 * we are affected is that we will have an obviously bogus
67 * timestamp on a trace event - i.e. not life threatening.
68 */
69u64 notrace trace_clock_jiffies(void)
70{
71 return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
72}
73EXPORT_SYMBOL_GPL(trace_clock_jiffies);
74
75/*
76 * trace_clock_global(): special globally coherent trace clock
77 *
78 * It has higher overhead than the other trace clocks but is still
79 * an order of magnitude faster than GTOD derived hardware clocks.
80 *
81 * Used by plugins that need globally coherent timestamps.
82 */
83
84/* keep prev_time and lock in the same cacheline. */
85static struct {
86 u64 prev_time;
87 arch_spinlock_t lock;
88} trace_clock_struct ____cacheline_aligned_in_smp =
89 {
90 .lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
91 };
92
93u64 notrace trace_clock_global(void)
94{
95 unsigned long flags;
96 int this_cpu;
97 u64 now;
98
99 raw_local_irq_save(flags);
100
101 this_cpu = raw_smp_processor_id();
102 now = sched_clock_cpu(this_cpu);
103 /*
104 * If in an NMI context then dont risk lockups and return the
105 * cpu_clock() time:
106 */
107 if (unlikely(in_nmi()))
108 goto out;
109
110 arch_spin_lock(&trace_clock_struct.lock);
111
112 /*
113 * TODO: if this happens often then maybe we should reset
114 * my_scd->clock to prev_time+1, to make sure
115 * we start ticking with the local clock from now on?
116 */
117 if ((s64)(now - trace_clock_struct.prev_time) < 0)
118 now = trace_clock_struct.prev_time + 1;
119
120 trace_clock_struct.prev_time = now;
121
122 arch_spin_unlock(&trace_clock_struct.lock);
123
124 out:
125 raw_local_irq_restore(flags);
126
127 return now;
128}
129EXPORT_SYMBOL_GPL(trace_clock_global);
130
131static atomic64_t trace_counter;
132
133/*
134 * trace_clock_counter(): simply an atomic counter.
135 * Use the trace_counter "counter" for cases where you do not care
136 * about timings, but are interested in strict ordering.
137 */
138u64 notrace trace_clock_counter(void)
139{
140 return atomic64_add_return(1, &trace_counter);
141}
1/*
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>
16#include <linux/irqflags.h>
17#include <linux/hardirq.h>
18#include <linux/module.h>
19#include <linux/percpu.h>
20#include <linux/sched.h>
21#include <linux/ktime.h>
22#include <linux/trace_clock.h>
23
24#include "trace.h"
25
26/*
27 * trace_clock_local(): the simplest and least coherent tracing clock.
28 *
29 * Useful for tracing that does not cross to other CPUs nor
30 * does it go through idle events.
31 */
32u64 notrace trace_clock_local(void)
33{
34 u64 clock;
35
36 /*
37 * sched_clock() is an architecture implemented, fast, scalable,
38 * lockless clock. It is not guaranteed to be coherent across
39 * CPUs, nor across CPU idle events.
40 */
41 preempt_disable_notrace();
42 clock = sched_clock();
43 preempt_enable_notrace();
44
45 return clock;
46}
47
48/*
49 * trace_clock(): 'between' trace clock. Not completely serialized,
50 * but not completely incorrect when crossing CPUs either.
51 *
52 * This is based on cpu_clock(), which will allow at most ~1 jiffy of
53 * jitter between CPUs. So it's a pretty scalable clock, but there
54 * can be offsets in the trace data.
55 */
56u64 notrace trace_clock(void)
57{
58 return local_clock();
59}
60
61
62/*
63 * trace_clock_global(): special globally coherent trace clock
64 *
65 * It has higher overhead than the other trace clocks but is still
66 * an order of magnitude faster than GTOD derived hardware clocks.
67 *
68 * Used by plugins that need globally coherent timestamps.
69 */
70
71/* keep prev_time and lock in the same cacheline. */
72static struct {
73 u64 prev_time;
74 arch_spinlock_t lock;
75} trace_clock_struct ____cacheline_aligned_in_smp =
76 {
77 .lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
78 };
79
80u64 notrace trace_clock_global(void)
81{
82 unsigned long flags;
83 int this_cpu;
84 u64 now;
85
86 local_irq_save(flags);
87
88 this_cpu = raw_smp_processor_id();
89 now = cpu_clock(this_cpu);
90 /*
91 * If in an NMI context then dont risk lockups and return the
92 * cpu_clock() time:
93 */
94 if (unlikely(in_nmi()))
95 goto out;
96
97 arch_spin_lock(&trace_clock_struct.lock);
98
99 /*
100 * TODO: if this happens often then maybe we should reset
101 * my_scd->clock to prev_time+1, to make sure
102 * we start ticking with the local clock from now on?
103 */
104 if ((s64)(now - trace_clock_struct.prev_time) < 0)
105 now = trace_clock_struct.prev_time + 1;
106
107 trace_clock_struct.prev_time = now;
108
109 arch_spin_unlock(&trace_clock_struct.lock);
110
111 out:
112 local_irq_restore(flags);
113
114 return now;
115}