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

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Date:	Thu, 25 Feb 2010 10:44:59 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	Frederic Weisbecker <fweisbec@...il.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, 2010-02-22 at 17:18 -0800, Tim Bird wrote:
> On 02/22/2010 10:17 AM, Frederic Weisbecker wrote:
> > 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 :)
> 
> I'll take a look at doing it this way, and see what I come
> up with.  If I can re-use most of trace_graph_entry and
> trace_graph_return (and I don't see why not), it should be
> a pretty small patch.

If you can get this out quickly, it may still be able to make the merge
window.

-- Steve


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