linux-kernel - Re: [RFC PATCH 00/11] mcount tracing utility

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Date:	Fri, 04 Jan 2008 01:42:32 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"William L. Irwin" <sparclinux@...r.kernel.org>
Subject: Re: [RFC PATCH 00/11] mcount tracing utility

Steven Rostedt <rostedt@...dmis.org> writes:

> The following patch series brings to vanilla Linux a bit of the RT kernel
> trace facility. This incorporates the "-pg" profiling option of gcc
> that will call the "mcount" function for all functions called in
> the kernel.
> [...]
> [Future:] SystemTap:
> ----------
> One thing that Arnaldo and I discussed last year was using systemtap to
> add hooks into the kernel to start and stop tracing.  

Sure.  The dual of this makes sense too: letting systemtap scripts
hook up to the mcount callback itself, for purposes beyond just
tracing the function calls.

> kprobes is too heavy to do on all funtion calls, but it would be
> perfect to add to non hot paths to start the tracer and stop the
> tracer.

(Note that kprobes are not the only event sources systemtap can use:
markers, timers, procfs control files, and some others.  Any
combination of these can be used in a script to express start/stop
decisions.)


- FChE
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