linux-kernel - Re: [PATCH 1/7] perf: Enable function tracing for perf core

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Message-ID: <1347288200.10751.17.camel@gandalf.local.home>
Date:	Mon, 10 Sep 2012 10:43:20 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/7] perf: Enable function tracing for perf core

On Sat, 2012-09-08 at 15:06 +0200, Frederic Weisbecker wrote:
> On Sat, Sep 08, 2012 at 07:55:16AM -0400, Steven Rostedt wrote:
> > According to Steven R. there is no reason left to not support
> > function tracing for the perf core. This makes it easier to debug
> > perf.
> > 
> > Don't remove -pg for the x86 and generic perf core.
> 
> Actually, perf can use function tracing. A good reason for disabling
> function tracing in perf is to avoid the overhead of recursive function
> tracing, even though we are protected against tracing re-entrancy, this
> still result in some overhead.

Yes, but perf shouldn't do a full function trace. It should be filtering
on what functions it wants to trace, and if it needs to, we can easily
make it not trace its own functions.

I've been thinking about adding function tracing into the trace
directory. As there's been several times I wanted it. The only files
that really shouldn't be traced in there is ftrace.c, trace_function.c
and trace_function_graph.c. The rest I believe is fair game.

-- Steve


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