linux-kernel - Re: [PATCH] ftrace: use only 5 byte nops for x86

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Message-ID: <48A608AF.5050307@zytor.com>
Date:	Fri, 15 Aug 2008 15:52:31 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>, srostedt@...hat.com
Subject: Re: [PATCH] ftrace: use only 5 byte nops for x86

Linus Torvalds wrote:
>>>
>> I think what we need to do is to test the NOPL instruction and create a
>> Linux-specific CPUID bit for it.  I'll do that and submit to tip:x86/cpu.
> 
> I also suspect that we'd really be much better off just fixing the generic 
> NOP tables for the 5-byte nop. As far as I could tell, from all the 
> numbers that have been posted, absolutely _none_ show that there is any 
> point at all to the 2-instruction 3/2-byte sequence.
> 
> So instead of having a magic special ftrace-only thing, why not just do it 
> right, and fix the generic 5-byte nop sequence?
> 

There is that, too.  The two are orthogonal.

	-hpa
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