linux-kernel - Re: [PATCH] Linux Kernel Markers

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Message-ID: <451187A5.4010501@opersys.com>
Date:	Wed, 20 Sep 2006 14:25:41 -0400
From:	Karim Yaghmour <karim@...rsys.com>
To:	"Frank Ch. Eigler" <fche@...hat.com>
CC:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Martin Bligh <mbligh@...gle.com>, prasanna@...ibm.com,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, 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>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Linux Kernel Markers

Hello Frank,

Frank Ch. Eigler wrote:
> My interpretation of Martin's Monday proposal is that, if implemented,
> we wouldn't need any of this nop/int3 stuff.  If function being
> instrumented were recompiled on-the-fly, then it could sport plain &
> direct C-level calls to the instrumentation handlers.

Absolutely. I guess the length of these threads is just fertile
ground for misunderstandings. Basically what Hiramatsu-san and
myself were discussing was just the mechanism for selecting/
forking in between the uninstrumented function and the instrumented
one.

So, to recap:

If you had 100,000 instrumentation points in the scheduler (obviously
a totally bogus number here ...) you'd have 2 functions:
1- one with no instrumentation at all, but with a 5byte filler such
   as the one presented by Hiramatsu-san.
2- one with the instrumentation.

Early in the proposal, the mechanics of switching in between "1" and "2"
seemed to be problematic, but I think with Hiramatsu-san's proposal
and, on the x86, djprobes, we've got it figured out.

Let me know if I'm not providing enough detail.

Thanks,

Karim

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