blob: 394783531cbb76d9f7d9ab34ae0b6963d5d14dff [file] [log] [blame]
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
Steven Rostedt8b2a5da2009-11-11 19:36:03 -050024#include "trace.h"
25
Ingo Molnar14131f22009-02-26 18:47:11 +010026/*
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{
Peter Zijlstra6cc3c6e2009-03-10 19:03:43 +010034 u64 clock;
35
Ingo Molnar14131f22009-02-26 18:47:11 +010036 /*
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 */
Steven Rostedt5168ae52010-06-03 09:36:50 -040041 preempt_disable_notrace();
Peter Zijlstra6cc3c6e2009-03-10 19:03:43 +010042 clock = sched_clock();
Steven Rostedt5168ae52010-06-03 09:36:50 -040043 preempt_enable_notrace();
Peter Zijlstra6cc3c6e2009-03-10 19:03:43 +010044
45 return clock;
Ingo Molnar14131f22009-02-26 18:47:11 +010046}
47
48/*
Lucas De Marchi25985ed2011-03-30 22:57:33 -030049 * trace_clock(): 'between' trace clock. Not completely serialized,
Ingo Molnar14131f22009-02-26 18:47:11 +010050 * 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{
Peter Zijlstrac6763292010-05-25 10:48:51 +020058 return local_clock();
Ingo Molnar14131f22009-02-26 18:47:11 +010059}
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
Steven Rostedt6ca6cca2009-09-15 12:24:22 -040071/* keep prev_time and lock in the same cacheline. */
72static struct {
73 u64 prev_time;
Thomas Gleixner445c8952009-12-02 19:49:50 +010074 arch_spinlock_t lock;
Steven Rostedt6ca6cca2009-09-15 12:24:22 -040075} trace_clock_struct ____cacheline_aligned_in_smp =
76 {
Thomas Gleixneredc35bd2009-12-03 12:38:57 +010077 .lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
Steven Rostedt6ca6cca2009-09-15 12:24:22 -040078 };
Ingo Molnar14131f22009-02-26 18:47:11 +010079
80u64 notrace trace_clock_global(void)
81{
82 unsigned long flags;
83 int this_cpu;
84 u64 now;
85
Li Zefane36673e2010-03-24 10:57:37 +080086 local_irq_save(flags);
Ingo Molnar14131f22009-02-26 18:47:11 +010087
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
Thomas Gleixner0199c4e2009-12-02 20:01:25 +010097 arch_spin_lock(&trace_clock_struct.lock);
Ingo Molnar14131f22009-02-26 18:47:11 +010098
99 /*
100 * TODO: if this happens often then maybe we should reset
Steven Rostedt6ca6cca2009-09-15 12:24:22 -0400101 * my_scd->clock to prev_time+1, to make sure
Ingo Molnar14131f22009-02-26 18:47:11 +0100102 * we start ticking with the local clock from now on?
103 */
Steven Rostedt6ca6cca2009-09-15 12:24:22 -0400104 if ((s64)(now - trace_clock_struct.prev_time) < 0)
105 now = trace_clock_struct.prev_time + 1;
Ingo Molnar14131f22009-02-26 18:47:11 +0100106
Steven Rostedt6ca6cca2009-09-15 12:24:22 -0400107 trace_clock_struct.prev_time = now;
Ingo Molnar14131f22009-02-26 18:47:11 +0100108
Thomas Gleixner0199c4e2009-12-02 20:01:25 +0100109 arch_spin_unlock(&trace_clock_struct.lock);
Ingo Molnar14131f22009-02-26 18:47:11 +0100110
111 out:
Li Zefane36673e2010-03-24 10:57:37 +0800112 local_irq_restore(flags);
Ingo Molnar14131f22009-02-26 18:47:11 +0100113
114 return now;
115}
Steven Rostedt62496872011-09-19 11:35:58 -0400116
117static atomic64_t trace_counter;
118
119/*
120 * trace_clock_counter(): simply an atomic counter.
121 * Use the trace_counter "counter" for cases where you do not care
122 * about timings, but are interested in strict ordering.
123 */
124u64 notrace trace_clock_counter(void)
125{
126 return atomic64_add_return(1, &trace_counter);
127}