linux-kernel - Re: [PATCH 2/2] tracing/function-return-tracer: Call prepare_ftrace

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Message-ID: <20081113094412.GL25479@elte.hu>
Date:	Thu, 13 Nov 2008 10:44:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing/function-return-tracer: Call
	prepare_ftrace_return by registers


* Frédéric Weisbecker <fweisbec@...il.com> wrote:

> 2008/11/13 Ingo Molnar <mingo@...e.hu>:
> > hm, function-exit is a quite bad name i think that tells nothing to
> > the user. I like "function-cost tracer" because that tells the user
> > what it's all about in the end.
> >
> > Or perhaps we could name it the "callgraph" tracer? (as opposed to the
> > simpler function tracer which traces function entries) Note that we
> > could use the output to build function call coverage graphs.
> 
> But you can build a call graph with the function tracer, that what 
> does the script draw_trace.py in a bit loosely way for example.

yes, but not reliably so - there's no guaranteed callgraph structure. 
With entry tracing we have entry+parent events, but especially across 
longer callchains there's no truly guaranteed way to preserve the full 
graph.

> IMHO, function cost measurement or call graphs are particular uses 
> that can be made of this engine. You can also use it to trace 
> function return values for example.

yes. The mockup output has place for that.

> So perhaps naming it by thinking on the purpose it could be use at 
> most would be better that its "general" or "potential" purpose. I 
> don't know...

i suggested "full-function" tracer name before, but that sounds a bit 
quirky too.

Perhaps this should be the function-tracer, and the entry tracer would 
be the function-entry tracer?

	Ingo
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