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

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Date:	Tue, 26 Sep 2006 15:08:49 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
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:
> >Hi,
> >
> >Ok, so as far as I can see, we can only control the execution flow by 
> >modifying
> >values in the output list of the asm.
> >
> >Do you think the following would work ?
> >
> >
> >#define MARK_JUMP(name, format, args...) \
> >        do { \
> >                char condition; \
> >                asm volatile(   ".section .markers, \"a\";\n\t" \
> >                                        ".long 0f;\n\t" \
> >                                        ".previous;\n\t" \
> >                                        "0:\n\t" \
> >                                        "movb $0,%1;\n\t" \
> >                                : "+m" (__marker_sequencer), \
> >                                "=r" (condition) : ); \
> >                if(unlikely(condition)) { \
> >                        MARK_CALL(name, format, ## args); \
> >                } \
> >        } while(0)
> >  
> 
> Yep, that looks reasonable.  Though you could just directly test a 
> per-marker enable flag, rather than using "condition"...
> 

The goal of the local variable "condition" here is that it will be forced to be
a register (=r in asm output), so there is no memory load involved (immediate
value).

I am not sure I understand your suggestion correctly.. do you mean having
a per-marker flag that would be loaded and tested at every marker site ?


Mathieu

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