thinkpad-acpi: convert to seq_file
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / trace / trace_clock.c
blobb588fd81f7f996792852e5035278736cdf9bec46
1 /*
2 * tracing clocks
4 * Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
6 * Implements 3 trace clock variants, with differing scalability/precision
7 * tradeoffs:
9 * - local: CPU-local trace clock
10 * - medium: scalable global clock with some jitter
11 * - global: globally monotonic, serialized clock
13 * Tracer plugins will chose a default from these clocks.
15 #include <linux/spinlock.h>
16 #include <linux/hardirq.h>
17 #include <linux/module.h>
18 #include <linux/percpu.h>
19 #include <linux/sched.h>
20 #include <linux/ktime.h>
21 #include <linux/trace_clock.h>
24 * trace_clock_local(): the simplest and least coherent tracing clock.
26 * Useful for tracing that does not cross to other CPUs nor
27 * does it go through idle events.
29 u64 notrace trace_clock_local(void)
31 unsigned long flags;
32 u64 clock;
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.
39 raw_local_irq_save(flags);
40 clock = sched_clock();
41 raw_local_irq_restore(flags);
43 return clock;
47 * trace_clock(): 'inbetween' trace clock. Not completely serialized,
48 * but not completely incorrect when crossing CPUs either.
50 * This is based on cpu_clock(), which will allow at most ~1 jiffy of
51 * jitter between CPUs. So it's a pretty scalable clock, but there
52 * can be offsets in the trace data.
54 u64 notrace trace_clock(void)
56 return cpu_clock(raw_smp_processor_id());
61 * trace_clock_global(): special globally coherent trace clock
63 * It has higher overhead than the other trace clocks but is still
64 * an order of magnitude faster than GTOD derived hardware clocks.
66 * Used by plugins that need globally coherent timestamps.
69 static u64 prev_trace_clock_time;
71 static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp =
72 (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
74 u64 notrace trace_clock_global(void)
76 unsigned long flags;
77 int this_cpu;
78 u64 now;
80 raw_local_irq_save(flags);
82 this_cpu = raw_smp_processor_id();
83 now = cpu_clock(this_cpu);
85 * If in an NMI context then dont risk lockups and return the
86 * cpu_clock() time:
88 if (unlikely(in_nmi()))
89 goto out;
91 __raw_spin_lock(&trace_clock_lock);
94 * TODO: if this happens often then maybe we should reset
95 * my_scd->clock to prev_trace_clock_time+1, to make sure
96 * we start ticking with the local clock from now on?
98 if ((s64)(now - prev_trace_clock_time) < 0)
99 now = prev_trace_clock_time + 1;
101 prev_trace_clock_time = now;
103 __raw_spin_unlock(&trace_clock_lock);
105 out:
106 raw_local_irq_restore(flags);
108 return now;