linux-kernel - Re: [PATCH 0/5] ftrace: to kill a daemon

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Date:	Sat, 9 Aug 2008 16:42:11 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Bodo Eggert <7eggert@....de>, Andi Kleen <andi@...stfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: [PATCH 0/5] ftrace: to kill a daemon

On Sat, 9 Aug 2008, Steven Rostedt wrote:
> On Sat, 9 Aug 2008, Bodo Eggert wrote:
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> > > On Sat, 9 Aug 2008, Andi Kleen wrote:
> > >> Steven Rostedt <rostedt@...dmis.org> writes:

> > >> > I'm stubborn, I want to get it right _and_ keep it fast.
> > >> 
> > >> For me it would seem better to just not use two part 5 byte nops
> > >> instead of adding such hacks.  I doubt there are that many of them
> > >> anyways. I bet you won't be able to measure any difference between the
> > >> different nop types in any macro benchmark.
> > > 
> > > I wish we had a true 5 byte nop. The alternative is a jmp 0, which is
> > > measurable.
> > 
> > Did you try short jumps? (0xeb 0x03 0x?? 0x?? 0x??)
> 
> What would those last three bytes be?

Anything, since the CPU will ignore them.

My hope is that different kinds of jump will behaver differently,
but I fear the side effect of the jmp (reread memory in case of 
self-modifying code) will cause the CPU to slow down anyway.
-- 
Is reading in the bathroom considered Multitasking?
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