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Date: Fri, 25 Apr 2008 08:57:20 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
       Jiri Slaby <jirislaby@gmail.com>, David Miller <davem@davemloft.net>,
       zdenek.kabelac@gmail.com, rjw@sisk.pl, paulmck@linux.vnet.ibm.com,
       akpm@linux-foundation.org, linux-ext4@vger.kernel.org,
       herbert@gondor.apana.org.au, penberg@cs.helsinki.fi, clameter@sgi.com,
       linux-kernel@vger.kernel.org,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       Andi Kleen <andi@firstfloor.org>, pageexec@freemail.hu,
       Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH 1/1] x86: fix text_poke
References: <20080425.021301.193689806.davem@davemloft.net> <1209343883-7991-1-git-send-email-jirislaby@gmail.com> <alpine.LFD.1.10.0804250759260.2779@woody.linux-foundation.org> <20080425151931.GA25510@elte.hu> <20080425152650.GA894@elte.hu> <alpine.LFD.1.10.0804250830200.2779@woody.linux-foundation.org> <20080425155000.GA4438@elte.hu>
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Ingo Molnar wrote:
> 
> text_poke() itself only applies/unapplies the LOCK prefix - a single 
> byte. We shouldnt be doing that at all: the cost of LOCK is 
> insignificant (a few cycles) and most systems are SMP anyway.
> 

Alas, on older CPUs the cost of LOCK can be massive.  The question is 
how much we really care - the embedded people (who would definitely be 
affected) will simply build UP kernels, and this only affects booting 
SMP kernels on UP.

	-hpa