linux-kernel - Re: i686 quirk for AMD Geode

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Date:	Sun, 8 Nov 2009 18:35:37 +0100
From:	Pavel Machek <pavel@....cz>
To:	Matteo Croce <technoboy85@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

Hi!

> The AMD Geode LX has an x86 id of 5 (i586) tought it's technically an i686:

It is not.


> root@...x:~# egrep '^(cpu family|model name|flags)' /proc/cpuinfo
> cpu family      : 5
> model name      : Geode(TM) Integrated Processor by AMD PCS
> flags           : fpu de pse tsc msr cx8 sep pge cmov clflush mmx
> mmxext 3dnowext 3dnow
> 
> indeed it has MMX, MMXEXT and CMOV, just lacks the long NOP instruction (NOPL).
> This patch adds a quirck to promote the Geode to an i686 and emulates
> the NOPL in the do_invalid_op trap, so the userspace never notices.
> Emulating the NOPL has minimum performance loss, emulating a NOPL
> takes 0.5 usecs
> and they are rarely used in x86

NOP should be fast, so this is bad idea.
								Pavel

-- 
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