linux-kernel - Re: [PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug

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Message-ID: <20080814212036.GD13814@one.firstfloor.org>
Date:	Thu, 14 Aug 2008 23:20:36 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <srostedt@...hat.com>,
	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>,
	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>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug

> 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.

-Andi
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