linux-kernel - Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)

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Date:	Fri, 22 Sep 2006 15:31:02 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	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 0.5 for Linux 2.6.17 (with probe management)

I hate AOL-style me-toos, but there's nothing to add to this mail.
Thanks for this coherent writeup Mathieu.

On Thu, Sep 21, 2006 at 05:42:48PM -0400, Mathieu Desnoyers wrote:
> Hi Ingo,
> 
> I clearly expressed my position in the previous emails, so did you. You argued
> about a use of tracing that is not relevant to my vision of reality, which is :
> 
> - Embedded systems developers won't want a breakpoint-based probe
> - High performance computing users won't want a breakpoint-based probe
> - djprobe is far away from being in an acceptable state on architectures with
>   very inconvenient erratas (x86).
> - kprobe and djprobe cannot access local variables in every cases
> 
> For those reasons, I prefer a jump-over-call approach which lets gcc give us the
> local variables. No need of DWARF or SystemTAP macro Kung Fu. Just C and a
> loadable module.
> 
> By no means is it a replacement for a completely dynamic breakpoint-based
> instrumentation mechanism. I really think that both mechanism should coexist.
> 
> This is my position : I let the distribution/user decide what is appropriate for
> their use. My goal is to provide them a flexible mechanism that takes the
> multiple variety of uses in account without performance impact if they are not
> willing to pay it to benefit from tracing.
> 
> With all due respect, yes, there are Linux users different from the typical
> Redhat client. If your vision is still limited to this scope after a 500
> emails debate, I am afraid that there is very little I can do about it in
> one more.
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