linux-kernel - Re: [PATCH 05/05] Linux Kernel Markers, non optimized architectures

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Message-ID: <20070216233825.GB28087@Krystal>
Date:	Fri, 16 Feb 2007 18:38:25 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Karim Yaghmour <karim.yaghmour@...ptiva.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, systemtap@...rces.redhat.com,
	ltt-dev@...fik.org
Subject: Re: [PATCH 05/05] Linux Kernel Markers, non optimized architectures

* Karim Yaghmour (karim.yaghmour@...ptiva.com) wrote:
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> Mathieu Desnoyers wrote:
> > The main goal of this config option is for embedded systems which doesn't 
> support live code modification. Maybe we can put that under "embedded 
> sytems" menu ?
> 
> Not sure whether you had had other feedback on this elsewhere in
> the rest of the thread, but yes, this would make sense if the
> "embedded" angle is the only reason we need this (and not, say,
> performance, etc.) Also, having done that, maybe it would make
> some sense to have it be a "disable" rather than "enable":
> CONFIG_MARKERS_DISABLE_OPTIMIZATION?
> 

Hi Karim,

Yes, that was indeed the first way I implemented it, as a "disable"
option. One of the main thing we have to figure out before I modify this
is if we want to have the generic version of markers available in a
"forced" manner at the marker site with the GEN_MARK macro instead of
the MARK macro (this is the actual implementation). It has proven to
be useful to instrument lockdep.c irq enable/disable tracing functions.
The reason why is because they are called just before the trap handler
returns and I need it to do XMC on x86 and x86_64. It would therefore
cause a recursive trap.

I think it makes sense to have this kind of support for hard-to-instrument
sites within the marker infrastructure, but the cost is to have two
marker flavors : MARK and GEN_MARK (but really GEN_MARK is only intended
for a few sites).

Mathieu

> Karim
> 
> 
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-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Candidate, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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