1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
// SPDX-License-Identifier: GPL-2.0
/*
* tracing clocks
*
* Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Implements 3 trace clock variants, with differing scalability/precision
* tradeoffs:
*
* - local: CPU-local trace clock
* - medium: scalable global clock with some jitter
* - global: globally monotonic, serialized clock
*
* Tracer plugins will chose a default from these clocks.
*/
#include <linux/spinlock.h>
#include <linux/irqflags.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/ktime.h>
#include <linux/trace_clock.h>
/*
* trace_clock_local(): the simplest and least coherent tracing clock.
*
* Useful for tracing that does not cross to other CPUs nor
* does it go through idle events.
*/
u64 notrace trace_clock_local(void)
{
u64 clock;
/*
* sched_clock() is an architecture implemented, fast, scalable,
* lockless clock. It is not guaranteed to be coherent across
* CPUs, nor across CPU idle events.
*/
preempt_disable_notrace();
clock = sched_clock();
preempt_enable_notrace();
return clock;
}
EXPORT_SYMBOL_GPL(trace_clock_local);
/*
* trace_clock(): 'between' trace clock. Not completely serialized,
* but not completely incorrect when crossing CPUs either.
*
* This is based on cpu_clock(), which will allow at most ~1 jiffy of
* jitter between CPUs. So it's a pretty scalable clock, but there
* can be offsets in the trace data.
*/
u64 notrace trace_clock(void)
{
return local_clock();
}
EXPORT_SYMBOL_GPL(trace_clock);
/*
* trace_jiffy_clock(): Simply use jiffies as a clock counter.
* Note that this use of jiffies_64 is not completely safe on
* 32-bit systems. But the window is tiny, and the effect if
* we are affected is that we will have an obviously bogus
* timestamp on a trace event - i.e. not life threatening.
*/
u64 notrace trace_clock_jiffies(void)
{
return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
}
EXPORT_SYMBOL_GPL(trace_clock_jiffies);
/*
* trace_clock_global(): special globally coherent trace clock
*
* It has higher overhead than the other trace clocks but is still
* an order of magnitude faster than GTOD derived hardware clocks.
*
* Used by plugins that need globally coherent timestamps.
*/
/* keep prev_time and lock in the same cacheline. */
static struct {
u64 prev_time;
arch_spinlock_t lock;
} trace_clock_struct ____cacheline_aligned_in_smp =
{
.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
};
u64 notrace trace_clock_global(void)
{
unsigned long flags;
int this_cpu;
u64 now, prev_time;
raw_local_irq_save(flags);
this_cpu = raw_smp_processor_id();
/*
* The global clock "guarantees" that the events are ordered
* between CPUs. But if two events on two different CPUS call
* trace_clock_global at roughly the same time, it really does
* not matter which one gets the earlier time. Just make sure
* that the same CPU will always show a monotonic clock.
*
* Use a read memory barrier to get the latest written
* time that was recorded.
*/
smp_rmb();
prev_time = READ_ONCE(trace_clock_struct.prev_time);
now = sched_clock_cpu(this_cpu);
/* Make sure that now is always greater than prev_time */
if ((s64)(now - prev_time) < 0)
now = prev_time + 1;
/*
* If in an NMI context then dont risk lockups and simply return
* the current time.
*/
if (unlikely(in_nmi()))
goto out;
/* Tracing can cause strange recursion, always use a try lock */
if (arch_spin_trylock(&trace_clock_struct.lock)) {
/* Reread prev_time in case it was already updated */
prev_time = READ_ONCE(trace_clock_struct.prev_time);
if ((s64)(now - prev_time) < 0)
now = prev_time + 1;
trace_clock_struct.prev_time = now;
/* The unlock acts as the wmb for the above rmb */
arch_spin_unlock(&trace_clock_struct.lock);
}
out:
raw_local_irq_restore(flags);
return now;
}
EXPORT_SYMBOL_GPL(trace_clock_global);
static atomic64_t trace_counter;
/*
* trace_clock_counter(): simply an atomic counter.
* Use the trace_counter "counter" for cases where you do not care
* about timings, but are interested in strict ordering.
*/
u64 notrace trace_clock_counter(void)
{
return atomic64_add_return(1, &trace_counter);
}
|
