Re: [PATCH 1/1] ftrace - add support for tracing_thresh to function_graph tracer

[Tim Bird <tim.bird@am.sony.com>]

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.

 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================