linux-kernel - Re: tracepoint maintainance models

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Message-ID: <20060918161526.GL3951@redhat.com>
Date:	Mon, 18 Sep 2006 12:15:26 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Ingo Molnar <mingo@...e.hu>, "Frank Ch. Eigler" <fche@...hat.com>,
	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

Hi -

alan wrote:

> [...] So its L1 misses more register reloads and the like. Sounds
> more and more like wasted clock cycles for debug. [...]

But it's not just "for debug"!  It is for system administrators,
end-users, developers.

> Its one thing to dump trace helper data into the kernel, its another
> when we all get to pay for it all the time when we don't need to
> [...]

Indeed, there will be some non-zero execution-time cost.  We must be
willing to pay *something* in order to enable this functionality.  One
question (still: http://lkml.org/lkml/2006/2/22/166) is trading
time/space cost; others include cross-platform vs. porting necessity;
robustness w.r.t. data-collectionand control-flow preservation.

- FChE

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