linux-kernel - Re: [PATCH 1/1] ftrace - add support for tracing_thresh to function

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Message-ID: <20100220142054.GA5354@nowhere>
Date:	Sat, 20 Feb 2010 15:21:04 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	Tim Bird <tim.bird@...sony.com>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ftrace - add support for tracing_thresh to
	function_graph tracer

On Thu, Feb 11, 2010 at 07:26:55PM -0500, Steven Rostedt wrote:
> On Thu, 2010-02-11 at 16:01 -0800, Tim Bird wrote:
> > On 02/11/2010 03:10 PM, Steven Rostedt wrote:
> > > On Wed, 2010-02-10 at 14:52 -0800, Tim Bird wrote:
> > >>  static struct tracer_opt trace_opts[] = {
> > >>  	/* Display overruns? (for self-debug purpose) */
> > >> @@ -53,6 +54,8 @@ static struct tracer_opt trace_opts[] = {
> > >>  	{ TRACER_OPT(funcgraph-duration, TRACE_GRAPH_PRINT_DURATION) },
> > >>  	/* Display absolute time of an entry */
> > >>  	{ TRACER_OPT(funcgraph-abstime, TRACE_GRAPH_PRINT_ABS_TIME) },
> > >> +	/* Display function name on exit, instead of just closing brace */
> > >> +	{ TRACER_OPT(funcgraph-exit, TRACE_GRAPH_PRINT_FUNC_EXIT) },
> > >>  	{ } /* Empty entry */
> > > 
> > > I wonder if this should be enabled on start up of the function graph
> > > tracer if the threshold is set?
> > > 
> > > Otherwise people will wonder WTF?
> > 
> > Indeed.  I'm not sure exactly how to do this.
> > 
> > Would it be better to set the option when current_tracer
> > is set with 'function_graph', and tracing_thresh is non-zero?
> 
> The above is the only one I would do. If tracing_thresh is non-zero when
> the function_graph tracer is set, on the start up code in the function
> tracer (graph_trace_init).
> 
> Just enable the option if trace_thresh is set. If you enable function
> graph tracer and have the trace_thresh set, then this type of tracing
> starts immediately. It also keeps the code nicely in the
> trace_function_graph.c file, and does not need to touch the setting of
> tracing_thresh.


Actually why do we encumber with both tracing_thresh and the funcgraph-exit
option?

We could just have the output and the record check tracing_thresh instead
of the funcgraph-exit option.

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