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ftrace: add nop tracer

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A no-op tracer which can serve two purposes:

 1. A template for development of a new tracer.
 2. A convenient way to see ftrace_printk() calls without
    an irrelevant trace making the output messy.

[ mingo@elte.hu: resolved conflicts ]
Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Steven Noonan 2008-09-19 03:06:43 -07:00 committed by Ingo Molnar
parent 5bf9a1ee35
commit fb1b6d8b51
5 changed files with 89 additions and 0 deletions
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10
kernel/trace/Kconfig
View File

@ -101,6 +101,16 @@ config SCHED_TRACER
This tracer tracks the latency of the highest priority task
to be scheduled in, starting from the point it has woken up.
config NOP_TRACER
bool "NOP Tracer"
depends on HAVE_FTRACE
depends on DEBUG_KERNEL
select TRACING
help
This tracer does nothing. The primary purpose for it is to
politely print the output of ftrace_printk() calls without
the overhead of an irrelevant trace taking place.
config CONTEXT_SWITCH_TRACER
bool "Trace process context switches"
depends on HAVE_FTRACE

1
kernel/trace/Makefile
View File

@ -19,6 +19,7 @@ obj-$(CONFIG_FTRACE) += trace_functions.o
obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o
obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
obj-$(CONFIG_NOP_TRACER) += trace_nop.o
obj-$(CONFIG_STACK_TRACER) += trace_stack.o
obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o

4
kernel/trace/trace.h
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@ -339,6 +339,10 @@ extern int trace_selftest_startup_preemptirqsoff(struct tracer *trace,
extern int trace_selftest_startup_wakeup(struct tracer *trace,
struct trace_array *tr);
#endif
#ifdef CONFIG_NOP_TRACER
extern int trace_selftest_startup_nop(struct tracer *trace,
struct trace_array *tr);
#endif
#ifdef CONFIG_CONTEXT_SWITCH_TRACER
extern int trace_selftest_startup_sched_switch(struct tracer *trace,
struct trace_array *tr);

65
kernel/trace/trace_nop.c Normal file
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@ -0,0 +1,65 @@
/*
* nop tracer
*
* Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
*
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/debugfs.h>
#include <linux/ftrace.h>
#include "trace.h"
static struct trace_array *ctx_trace;
static void start_nop_trace(struct trace_array *tr)
{
/* Nothing to do! */
}
static void stop_nop_trace(struct trace_array *tr)
{
/* Nothing to do! */
}
static void nop_trace_init(struct trace_array *tr)
{
ctx_trace = tr;
if (tr->ctrl)
start_nop_trace(tr);
}
static void nop_trace_reset(struct trace_array *tr)
{
if (tr->ctrl)
stop_nop_trace(tr);
}
static void nop_trace_ctrl_update(struct trace_array *tr)
{
/* When starting a new trace, reset the buffers */
if (tr->ctrl)
start_nop_trace(tr);
else
stop_nop_trace(tr);
}
static struct tracer nop_trace __read_mostly =
{
.name = "nop",
.init = nop_trace_init,
.reset = nop_trace_reset,
.ctrl_update = nop_trace_ctrl_update,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_nop,
#endif
};
__init static int init_nop_trace(void)
{
return register_tracer(&nop_trace);
}
device_initcall(init_nop_trace);

9
kernel/trace/trace_selftest.c
View File

@ -418,6 +418,15 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
}
#endif /* CONFIG_IRQSOFF_TRACER && CONFIG_PREEMPT_TRACER */
#ifdef CONFIG_NOP_TRACER
int
trace_selftest_startup_nop(struct tracer *trace, struct trace_array *tr)
{
/* What could possibly go wrong? */
return 0;
}
#endif
#ifdef CONFIG_SCHED_TRACER
static int trace_wakeup_test_thread(void *data)
{