linux-kernel - Re: tracepoint maintainance models

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Date:	Mon, 18 Sep 2006 17:42:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Andrew Morton <akpm@...l.org>,
	Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	Michel Dagenais <michel.dagenais@...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


* Frank Ch. Eigler <fche@...hat.com> wrote:

> > I think your implementation is questionable if it causes any kind of 
> > jumps and conditions, even marked unlikely. Just put the needed data 
> > in a seperate section which can be used by the debugging tools. 
> > [...] No need to actually mess with the code for the usual cases.
> 
> Trouble is that it is specifically the *unusual* cases that need 
> compiler assistance via static markers, otherwise we'd manage with 
> just k/djprobes & debuginfo type efforts.

i think it's all fine as long as it's just a single 5-byte NOP that we 
are inserting - because in the *usual* case the 'parameter access 
side-effects' should have no effect. They will have an effect in the 
*unusual* case though, but that's very much by design - and it's not a 
performance issue because it's 1) unusual, 2) at most means a bit 
different code organization by gcc. It very likely wont mean any extra 
branches even in the unusual case. Or do i underestimate the scope of 
the problem? ;-)

	Ingo
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