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Date: Fri, 19 Sep 2008 03:02:04 -0700
From: Steven Noonan <steven@...inklabs.net>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, Steven Noonan <steven@...inklabs.net>
Subject: [PATCH -tip] ftrace: add nop tracer
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.
Signed-off-by: Steven Noonan <steven@...inklabs.net>
---
kernel/trace/Kconfig | 10 ++++++
kernel/trace/Makefile | 1 +
kernel/trace/trace.h | 4 ++
kernel/trace/trace_nop.c | 66 +++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_selftest.c | 9 +++++
5 files changed, 90 insertions(+), 0 deletions(-)
create mode 100644 kernel/trace/trace_nop.c
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 16e5bb5..d7b2de7 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -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
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 58ec61c..73ba13f 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -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
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 42f65d0..447d4b9 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -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);
diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
new file mode 100644
index 0000000..b0a88e6
--- /dev/null
+++ b/kernel/trace/trace_nop.c
@@ -0,0 +1,66 @@
+/*
+ * nop tracer
+ *
+ * Copyright (C) 2008 Steven Noonan <steven@...inklabs.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)
+{
+ printk ( "Registering tracer 'nop' before your very eyes!\n" );
+ return register_tracer(&nop_trace);
+}
+device_initcall(init_nop_trace);
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 630715b..82db910 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -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)
{
--
1.6.0.2
--
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