linux-kernel - Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

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Date:	15 Sep 2006 05:29:24 -0400
From:	Jes Sorensen <jes@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Martin Bligh <mbligh@...igh.org>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	Michel Dagenais <michel.dagenais@...ymtl.ca>, fche@...hat.com
Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

>>>>> "Ingo" == Ingo Molnar <mingo@...e.hu> writes:

Ingo> * Martin Bligh <mbligh@...igh.org> wrote:

>> I don't think anyone is saying that static tracepoints do not have
>> their limitations, or that dynamic tracepointing is useless. But
>> that's not the point ... why can't we have one infrastructure that
>> supports both? Preferably in a fairly simple, consistent way.

Ingo> primarily because i fail to see any property of static tracers
Ingo> that are not met by dynamic tracers. So to me dynamic tracers
Ingo> like SystemTap are a superset of static tracers.

Ingo> So my position is that what we should concentrate on is to make
Ingo> the life of dynamic tracers easier (be that a handful of
Ingo> generic, parametric hooks that gather debuginfo information and
Ingo> add NOPs for easy patching), while realizing that static tracers
Ingo> have no advantage over dynamic tracers.

The parallel that springs to mind here is C++ kernel components 'I
promise to only use the good parts', then next week someone else adds
another pile in a worse place. Once the points are in we will never
get rid of them, look at how long it took to get rid of devfs :( In
addition it is guaranteed that people will not be able to agree on
which points to put where, despite the claim that there will be only
30 points - sorry, I am not buying that, we have plenty of evidence to
show the opposite.

I looked at the old LTT code a while ago and it was pretty appalling,
maybe LTTng is better, but I can't say the old code gave me a warm
fuzzy feeling.

Jes
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