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

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Date:	Thu, 11 Feb 2010 19:26:55 -0500
From:	Steven Rostedt <srostedt@...hat.com>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/1] ftrace - add support for tracing_thresh to
 function_graph tracer

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.

-- Steve


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