linux-kernel - Re: [PATCH 2/3] ftrace: add ftrace-buffer option

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Date:	Mon, 2 Nov 2015 17:56:00 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/3] ftrace: add ftrace-buffer option

On Mon,  2 Nov 2015 17:42:43 -0500
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> In order to use ftrace tracers to generate tracepoints without doing
> tracing to its own hardcoded ring buffers, add a ftrace-buffer option
> (default: 1). When set to 0, it disables tracing into the ftrace
> hardcoded buffers.
> 

This needs a more in depth change log. I have no idea why this is
needed.

Also, the trace_options code have been redesigned, and this won't apply
to it (see linux-next). Also, if this is only for irqsoff latency
tracers, it should be a tracer option, not a global one.

-- Steve


> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Peter Zijlstra <peterz@...radead.org>
> ---
>  kernel/trace/trace.c         |  4 +++-
>  kernel/trace/trace.h         |  1 +
>  kernel/trace/trace_irqsoff.c | 19 +++++++++++--------
>  3 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 6e79408..d664f0e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -472,7 +472,8 @@ static inline void trace_access_lock_init(void)
>  unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
>  	TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
>  	TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
> -	TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
> +	TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION |
> +	TRACE_ITER_FTRACE_BUFFER;
>  
>  static void tracer_tracing_on(struct trace_array *tr)
>  {
> @@ -862,6 +863,7 @@ static const char *trace_options[] = {
>  	"irq-info",
>  	"markers",
>  	"function-trace",
> +	"ftrace-buffer",
>  	NULL
>  };
>  
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 74bde81..29968e1 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -930,6 +930,7 @@ enum trace_iterator_flags {
>  	TRACE_ITER_IRQ_INFO		= 0x800000,
>  	TRACE_ITER_MARKERS		= 0x1000000,
>  	TRACE_ITER_FUNCTION		= 0x2000000,
> +	TRACE_ITER_FTRACE_BUFFER	= 0x4000000,
>  };
>  
>  /*
> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
> index 8523ea3..3e5635d 100644
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -334,9 +334,11 @@ check_critical_timing(struct trace_array *tr,
>  	if (!report_latency(tr, delta))
>  		goto out_unlock;
>  
> -	__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> -	/* Skip 5 functions to get to the irq/preempt enable function */
> -	__trace_stack(tr, flags, 5, pc);
> +	if (trace_flags & TRACE_ITER_FTRACE_BUFFER) {
> +		__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> +		/* Skip 5 functions to get to the irq/preempt enable function */
> +		__trace_stack(tr, flags, 5, pc);
> +	}
>  
>  	if (data->critical_sequence != max_sequence)
>  		goto out_unlock;
> @@ -356,7 +358,8 @@ out_unlock:
>  out:
>  	data->critical_sequence = max_sequence;
>  	data->preempt_timestamp = ftrace_now(cpu);
> -	__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
> +	if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
> +		__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
>  }
>  
>  static inline void
> @@ -387,9 +390,8 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip)
>  	data->critical_start = parent_ip ? : ip;
>  
>  	local_save_flags(flags);
> -
> -	__trace_function(tr, ip, parent_ip, flags, preempt_count());
> -
> +	if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
> +		__trace_function(tr, ip, parent_ip, flags, preempt_count());
>  	per_cpu(tracing_cpu, cpu) = 1;
>  
>  	atomic_dec(&data->disabled);
> @@ -422,7 +424,8 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
>  	atomic_inc(&data->disabled);
>  
>  	local_save_flags(flags);
> -	__trace_function(tr, ip, parent_ip, flags, preempt_count());
> +	if (trace_flags & TRACE_ITER_FTRACE_BUFFER)
> +		__trace_function(tr, ip, parent_ip, flags, preempt_count());
>  	check_critical_timing(tr, data, parent_ip ? : ip, cpu);
>  	data->critical_start = 0;
>  	atomic_dec(&data->disabled);

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