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

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Message-ID: <20100222181705.GF5055@nowhere>
Date:	Mon, 22 Feb 2010 19:17:08 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Tim Bird <tim.bird@...sony.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 1/1] ftrace - add support for tracing_thresh to
	function_graph tracer

On Mon, Feb 22, 2010 at 09:57:43AM -0500, Steven Rostedt wrote:
> On Sat, 2010-02-20 at 15:43 +0100, Frederic Weisbecker wrote:
> > 
> > Instead of having yet another check here, may be should we
> > have a dedicated stub trace_graph_entry?
> > 
> > 
> > 
> > > @@ -254,6 +263,10 @@ static void __trace_graph_return(struct trace_array *tr,
> > >  	if (unlikely(__this_cpu_read(per_cpu_var(ftrace_cpu_disabled))))
> > >  		return;
> > >  
> > > +	if (tracing_thresh &&
> > > +		(trace->rettime - trace->calltime < tracing_thresh))
> > > +		return;
> > > +
> > 
> > 
> > 
> > And perhaps we can do the same for the return handler?
> > We could have a trace_graph_return_threshold that
> > performs the above check and then relies on trace_graph_return.
> 
> So you mean to register a different type of function to the graph tracer
> if trace_thresh is enabled? That does sound like a better idea.


Yeah, this is going to optimize both types of tracing. And I would
also like to prevent from adding new checks in the common graph
tracing if possible. User's cpus and cachelines deserve better :)

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