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Date: Fri, 19 Sep 2008 12:48:16 +0200
From: "Frédéric Weisbecker" <fweisbec@...il.com>
To: "Steven Noonan" <steven@...inklabs.net>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH -tip FIXED] ftrace: add nop tracer
2008/9/19 Steven Noonan <steven@...inklabs.net>:
> 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 | 65 +++++++++++++++++++++++++++++++++++++++++
> kernel/trace/trace_selftest.c | 9 ++++++
> 5 files changed, 89 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..dafaefb
> --- /dev/null
> +++ b/kernel/trace/trace_nop.c
> @@ -0,0 +1,65 @@
> +/*
> + * 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)
> +{
> + 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
>
Hi Steven and Ingo!
It seems we have two "none" tracers now.
Why not seeing this nop tracer as an improvment of the current "none tracer" ?
As a result the none tracer contained in trace.c could be replaced by
this new one as the default tracer. And that's said, that will enable
trace_printk by default even when no tracer is selected by the user.
What do you think about it?
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