linux-kernel - Re: tracepoint maintainance models

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Date:	Sun, 17 Sep 2006 17:09:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Karim Yaghmour <karim@...rsys.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Jes Sorensen <jes@....com>,
	Andrew Morton <akpm@...l.org>,
	Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Cohen <wcohen@...hat.com>,
	"Martin J. Bligh" <mbligh@...igh.org>
Subject: Re: tracepoint maintainance models


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

> Hi,
> 
> On Sun, 17 Sep 2006, Ingo Molnar wrote:
> 
> > > This thread would be much better off talking about how to go about 
> > > implementing lightweight markers rather than spent on mindless rants.
> > 
> > i agree, as long as it's lightweight markers for _dynamic tracers_, so 
> > that we keep our options open - as per the arguments above.
> 
> Could you please explain, why we can't have markers which are usable 
> by any tracer?

the main reason for that i explained in the portion of the email you 
snipped:

> > On the other hand, if we accept static tracers into the mainline 
> > kernel, we have to decide in favor of tracepoint-maintainance model
> > #1 _FOREVER_. It will be a point of no return for a likely long
> > time. Moving a static tracepoint or even breaking it will cause 
> > end-user pain that needs an _upstream kernel fix_. It needs a new 
> > stable kernel, etc., etc. It is very inflexible, and fundamentally
> > so.

of course it's easy to have static markup that is usable for both types 
of tracers - but that is of little use. Static tracers also need the 
guarantee of a _full set_ of static markups. It is that _guarantee_ of a 
full set that i'm arguing against primarily. Without that guarantee it's 
useless to have markups that can be used by static tracers as well: you 
wont get a full set of tracepoints and the end-user will complain. 
(partial static markups are of course still very useful to dynamic 
tracers)

( furthermore, there are other reasons as well: i explained my position 
  in some of those replies that you did not want to "further dvelve 
  into". I'm happy to give you Message-IDs if you'd like to follow up on 
  them, there's no need to repeat them here. )

	Ingo
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