linux-kernel - Re: [PATCH] Linux Kernel Markers 0.13 for 2.6.17

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Message-ID: <20060926002551.GA18276@Krystal>
Date:	Mon, 25 Sep 2006 20:25:51 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	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>,
	Ingo Molnar <mingo@...e.hu>, 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>,
	Karim Yaghmour <karim@...rsys.com>,
	Pavel Machek <pavel@...e.cz>, Joe Perches <joe@...ches.com>,
	"Randy.Dunlap" <rdunlap@...otime.net>,
	"Jose R. Santos" <jrs@...ibm.com>
Subject: Re: [PATCH] Linux Kernel Markers 0.13 for 2.6.17

* Jeremy Fitzhardinge (jeremy@...p.org) wrote:
> Mathieu Desnoyers wrote:
> >Just as a precision :
> >
> >The following sequence (please refer to the code below for local symbols
> >1 and 2) :
> >
> >1:
> >preempt_disable()
> >call (*__mark_call_##name)(format, ## args);
> >preempt_enable_no_resched()
> >2:
> >
> >is insured because :
> >
> >1 is part of an inline assembly with rw dependency on __marker_sequencer
> >the call is surrounded by memory barriers.
> >2 is part of an inline assembly with rw dependency on __marker_sequencer
> >  
> 
> What do you mean the call is surrounded by memory barriers?  Do you mean 
> a call has an implicit barrier, or something else?
> 
Yes, preempt_disable() has a barrier(), on gcc :
__asm__ __volatile__("": : :"memory").


> Either way, this doesn't prevent some otherwise unrelated 
> non-memory-using code from being scheduled in there, which would not be 
> executed.  The gcc manual really strongly discourages jumping between 
> inline asms, because they have basically unpredictable results.
> 

Ok, I will do the call in assembly then.

Mathieu


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