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

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Date:	Sat, 16 Sep 2006 10:23:28 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, karim@...rsys.com,
	Andrew Morton <akpm@...l.org>,
	Paul Mundt <lethal@...ux-sh.org>, Jes Sorensen <jes@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	Michel Dagenais <michel.dagenais@...ymtl.ca>
Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108


* Roman Zippel <zippel@...ux-m68k.org> wrote:

> > > > Secondly, even people who intend to _eventually_ make use of 
> > > > tracing, dont use it most of the time. So why should they have 
> > > > more overhead when they are not tracing? Again: the point is not 
> > > > moot because even though the user intends to use tracing, but 
> > > > does not always want to trace.
> > > 
> > > I've used kernels which included static tracing and the perfomance 
> > > overhead is negligible for occasional use.
> > 
> > how does this suddenly make my point, that "a marker for dynamic 
> > tracing has lower performance impact than a static tracepoint, on 
> > systems that are not being traced", "moot"?
> 
> Why exactly is the point relevant in first place? How exactly is the 
> added (minor!) overhead such a fundamental problem?

how could a fundamental performance difference between two markup 
schemes be not relevant to kernel design decisions? Which performance 
difference i claim derives straight from the conceptual difference 
between the two approaches and is thus "unfixable" (and not an 
"implementational issue").

	Ingo
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