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Date: Thu, 14 Aug 2008 14:43:10 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       Ingo Molnar <mingo@elte.hu>, Jeremy Fitzhardinge <jeremy@goop.org>,
       Harvey Harrison <harvey.harrison@gmail.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Steven Rostedt <srostedt@redhat.com>,
       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>, Roland McGrath <roland@redhat.com>,
       Ulrich Drepper <drepper@redhat.com>,
       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>,
       Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible
 kernel and CPU hotplug
References: <20080814205815.GA14076@Krystal> <20080814212036.GD13814@one.firstfloor.org>
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Andi Kleen wrote:
>> So, unless these calculus are completely bogus, the difference between the nop
>> and the DS case seems not to be statistically significant.
> 
> My understanding was that the nops only make a measurable difference in the 
> -pg/mcount/ftrace patched out case where every function call starts with a 5
> byte nop.
> 
> Presumably function calls are much more common than lock prefix operations.

Yeah, although the LOCK prefix was measurable.

	-hpa