linux-kernel - Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

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Date:	Fri, 15 Sep 2006 20:23:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, karim@...rsys.com,
	Roman Zippel <zippel@...ux-m68k.org>,
	Tim Bird <tim.bird@...sony.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	Michel Dagenais <michel.dagenais@...ymtl.ca>
Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108


* Frank Ch. Eigler <fche@...hat.com> wrote:

> > Why are your despatching overheads 1000 cycles ? (and if its due to 
> > int3 why are you using int 3 8))
> 
> Smart teams from IBM and Hitachi have been hammering away at this code 
> for a year or two now, and yet (roughly) here we are.  There have been 
> experiments involving plopping branches instead of int3's at probe 
> locations, but this is self-modifying code involving multiple 
> instructions, and appears to be tricky on SMP/preempt boxes.

i am talking to them about that, and i'm 100% sure the solution is much 
easier than the many (much harder) problems that SystemTap has already 
solved. I think you are way too modest to realize how powerful (and 
important) SystemTap is :-)

	Ingo
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