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

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Message-ID: <48A459B1.2070601@zytor.com>
Date:	Thu, 14 Aug 2008 09:13:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	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>
Subject: Re: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with	preemptible
 kernel and CPU hotplug

Mathieu Desnoyers wrote:
> 
> I can't argue about the benefit of using VM CPU pinning to manage
> resources because I don't use it myself, but I ran some tests out of
> curiosity to find if uncontended locks were that cheap, and it turns out
> they aren't. Here are the results :
> 
> Xeon 2.0GHz
> 
> Summary
> 
> make -j1 kernel/      33.94 +/- 0.07         34.91 +/- 0.27      2.8 %
> hackbench 50           2.99 +/- 0.01          3.74 +/- 0.01     25.1 %
> 
> 1 CPU, replace smp lock prefixes with DS segment selector prefixes
> 1 CPU, noreplace-smp

For reference, could you also compare replace smp lock with NOPs?

	-hpa
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