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Date: Fri, 15 Aug 2008 15:44:10 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: "H. Peter Anvin" <hpa@zytor.com>
cc: Ingo Molnar <mingo@elte.hu>, Jeremy Fitzhardinge <jeremy@goop.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       David Miller <davem@davemloft.net>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
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       Rusty Russell <rusty@rustcorp.com.au>,
       Gregory Haskins <ghaskins@novell.com>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       "Luis Claudio R. Goncalves" <lclaudio@uudg.org>,
       Clark Williams <williams@redhat.com>, srostedt@redhat.com
Subject: Re: [PATCH] ftrace: use only 5 byte nops for x86
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On Fri, 15 Aug 2008, H. Peter Anvin wrote:

> Ingo Molnar wrote:
> > > > 
> > > > TODO: Examine the cpuid to determine the nop to use.
> > > >   
> > > Don't think that will help in general.  qemu claims its a Pentium II.
> > 
> > ok. I've applied Steve's patch as it's a good bugfix. The extra paranoia
> > about faulting on 0x90 seems excessive but doesnt hurt ;-)
> > 
> 
> 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?

		Linus