tracing: implement trace_clock_*() APIs

Impact: implement new tracing timestamp APIs

Add three 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

Make the ring-buffer use the local trace clock internally.

Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2009-02-26 18:47:11 +01:00
parent 6409c4da28
commit 14131f2f98
4 changed files with 123 additions and 3 deletions

View file

@ -0,0 +1,19 @@
#ifndef _LINUX_TRACE_CLOCK_H
#define _LINUX_TRACE_CLOCK_H
/*
* 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
*/
#include <linux/compiler.h>
#include <linux/types.h>
extern u64 notrace trace_clock_local(void);
extern u64 notrace trace_clock(void);
extern u64 notrace trace_clock_global(void);
#endif /* _LINUX_TRACE_CLOCK_H */

View file

@ -19,6 +19,7 @@ obj-$(CONFIG_FUNCTION_TRACER) += libftrace.o
obj-$(CONFIG_RING_BUFFER) += ring_buffer.o
obj-$(CONFIG_TRACING) += trace.o
obj-$(CONFIG_TRACING) += trace_clock.o
obj-$(CONFIG_TRACING) += trace_output.o
obj-$(CONFIG_TRACING) += trace_stat.o
obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o

View file

@ -4,6 +4,7 @@
* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/ring_buffer.h>
#include <linux/trace_clock.h>
#include <linux/ftrace_irq.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
@ -12,7 +13,6 @@
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/sched.h> /* used for sched_clock() (for now) */
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/list.h>
@ -112,14 +112,13 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0
/* FIXME!!! */
u64 ring_buffer_time_stamp(int cpu)
{
u64 time;
preempt_disable_notrace();
/* shift to debug/test normalization and TIME_EXTENTS */
time = sched_clock() << DEBUG_SHIFT;
time = trace_clock_local() << DEBUG_SHIFT;
preempt_enable_no_resched_notrace();
return time;

101
kernel/trace/trace_clock.c Normal file
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@ -0,0 +1,101 @@
/*
* 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/hardirq.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/ktime.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)
{
/*
* sched_clock() is an architecture implemented, fast, scalable,
* lockless clock. It is not guaranteed to be coherent across
* CPUs, nor across CPU idle events.
*/
return sched_clock();
}
/*
* trace_clock(): 'inbetween' 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 cpu_clock(raw_smp_processor_id());
}
/*
* 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.
*/
static u64 prev_trace_clock_time;
static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp =
(raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
u64 notrace trace_clock_global(void)
{
unsigned long flags;
int this_cpu;
u64 now;
raw_local_irq_save(flags);
this_cpu = raw_smp_processor_id();
now = cpu_clock(this_cpu);
/*
* If in an NMI context then dont risk lockups and return the
* cpu_clock() time:
*/
if (unlikely(in_nmi()))
goto out;
__raw_spin_lock(&trace_clock_lock);
/*
* TODO: if this happens often then maybe we should reset
* my_scd->clock to prev_trace_clock_time+1, to make sure
* we start ticking with the local clock from now on?
*/
if ((s64)(now - prev_trace_clock_time) < 0)
now = prev_trace_clock_time + 1;
prev_trace_clock_time = now;
__raw_spin_unlock(&trace_clock_lock);
out:
raw_local_irq_restore(flags);
return now;
}