linux-kernel - Re: i686 quirk for AMD Geode

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Date:	Sun, 08 Nov 2009 14:10:24 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>, Pavel Machek <pavel@....cz>
CC:	Matteo Croce <technoboy85@...il.com>,
	Sven-Haegar Koch <haegar@...net.de>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

Keep in mind that if we end up running that on code with any kind of significant fraction of CMOV it will utterly suck.  Count 500-odd cycles per emulated instruction.  It *is* still useful in some cases - which is why we have x87 emulation already, for example.  The question is mostly where the point of diminishing returns go.  In theory we could provide a full x86 interpreter (perhaps shared with KVM?) which would allow any instruction at all to be executed.

"Alan Cox" <alan@...rguk.ukuu.org.uk> wrote:

>> > Better to be sure that a NOPL whouldn't SIGILL your program, isn't
>> > it?
>> 
>> SIGILL is easier to debug than NOPL mysteriously taking 100x time it
>> should, sorry.
>
>And a working 686 distribution is a great deal more useful to end users,
>who outnumber you by a few million to one. It's a very sensible patch, or
>perhaps you'd prefer we didn't say. And you forget the user "debug" for
>a Geode + i686 without this will be "it hangs when I try and boot the
>install CD"
>
>It would probably also be worth having cmov fixups for the VIA C3 as well.
>
>Alan

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