linux-kernel - Re: [PATCH 3/3] trace: let boot trace be chosen by command line

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Date:	Tue, 3 Feb 2009 10:31:02 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 3/3] trace: let boot trace be chosen by command line

On Mon, Feb 02, 2009 at 09:38:33PM -0500, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> Now that we have a working ftrace=<tracer> function, make the boot
> tracer get activated by it. This way we can turn it on or off without
> recompiling the kernel, as well as keeping the selftests on. The
> selftests are disabled whenever a default tracer starts running.
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  kernel/trace/Kconfig      |    7 +++----
>  kernel/trace/trace.c      |    5 +----
>  kernel/trace/trace_boot.c |   11 +++++++----
>  3 files changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 2780665..8115daf 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -164,9 +164,8 @@ config BOOT_TRACER
>  	  representation of the delays during initcalls - but the raw
>  	  /debug/tracing/trace text output is readable too.
>  
> -	  ( Note that tracing self tests can't be enabled if this tracer is
> -	    selected, because the self-tests are an initcall as well and that
> -	    would invalidate the boot trace. )
> +	  You must pass in ftrace=initcall to the kernel command line
> +	  to enable this on bootup.
>  
>  config TRACE_BRANCH_PROFILING
>  	bool "Trace likely/unlikely profiler"
> @@ -328,7 +327,7 @@ config FTRACE_SELFTEST
>  
>  config FTRACE_STARTUP_TEST
>  	bool "Perform a startup test on ftrace"
> -	depends on TRACING && DEBUG_KERNEL && !BOOT_TRACER
> +	depends on TRACING && DEBUG_KERNEL
>  	select FTRACE_SELFTEST
>  	help
>  	  This option performs a series of startup tests on ftrace. On bootup
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 2c720c7..40edef4 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3167,12 +3167,9 @@ __init static int tracer_alloc_buffers(void)
>  	trace_init_cmdlines();
>  
>  	register_tracer(&nop_trace);
> +	current_trace = &nop_trace;
>  #ifdef CONFIG_BOOT_TRACER
>  	register_tracer(&boot_tracer);
> -	current_trace = &boot_tracer;
> -	current_trace->init(&global_trace);
> -#else
> -	current_trace = &nop_trace;
>  #endif
>  	/* All seems OK, enable tracing */
>  	tracing_disabled = 0;
> diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
> index 0e94b3d..1f07895 100644
> --- a/kernel/trace/trace_boot.c
> +++ b/kernel/trace/trace_boot.c
> @@ -28,13 +28,13 @@ void start_boot_trace(void)
>  
>  void enable_boot_trace(void)
>  {
> -	if (pre_initcalls_finished)
> +	if (boot_trace && pre_initcalls_finished)
>  		tracing_start_sched_switch_record();
>  }
>  
>  void disable_boot_trace(void)
>  {
> -	if (pre_initcalls_finished)
> +	if (boot_trace && pre_initcalls_finished)
>  		tracing_stop_sched_switch_record();
>  }
>  
> @@ -43,6 +43,9 @@ static int boot_trace_init(struct trace_array *tr)
>  	int cpu;
>  	boot_trace = tr;
>  
> +	if (!tr)
> +		return 0;
> +
>  	for_each_cpu(cpu, cpu_possible_mask)
>  		tracing_reset(tr, cpu);
>  
> @@ -132,7 +135,7 @@ void trace_boot_call(struct boot_trace_call *bt, initcall_t fn)
>  	unsigned long irq_flags;
>  	struct trace_array *tr = boot_trace;
>  
> -	if (!pre_initcalls_finished)
> +	if (!tr || !pre_initcalls_finished)
>  		return;
>  
>  	/* Get its name now since this function could
> @@ -164,7 +167,7 @@ void trace_boot_ret(struct boot_trace_ret *bt, initcall_t fn)
>  	unsigned long irq_flags;
>  	struct trace_array *tr = boot_trace;
>  
> -	if (!pre_initcalls_finished)
> +	if (!tr || !pre_initcalls_finished)
>  		return;
>  
>  	sprint_symbol(bt->func, (unsigned long)fn);
> -- 
> 1.5.6.5
> 
> -- 

Thanks, now I should turn out the initcall_debug dependency for the boot tracer
to actually trace. I should even make it trace the async calls BTW ...

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