linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <4AF9D8E2.7050205@zytor.com>
Date:	Tue, 10 Nov 2009 13:19:30 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Willy Tarreau <w@....eu>
CC:	Pavel Machek <pavel@....cz>, Avi Kivity <avi@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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

On 11/10/2009 01:12 PM, Willy Tarreau wrote:
> yes, just like with emulated FPU or trapped unaligned accesses. It's
> just like flying fishes. They exist but they aren't the most common
> ones. If people encounter these cases on a specific program, then
> they just have to recompile it if it is a problem. At least they
> don't rebuild the whole distro. And once again, I've been using
> cmpxchg/bswap emulation for years on my i386 without feeling any
> need for a rebuild, and CMOV emulation for years now on my mini-itx 
> C3 without any problem either. These are real experiences, not just
> fears of imaginary problems. Yes I can design a program to run 400
> times slower on these machines if I want. I just don't feel the need
> to do so and apparently existing programs' authors didn't either.

Willy, perhaps you can come up with a list of features you think should
be emulated, together with an explanation of why you opted for that list
of features and *did not* opt for others.

Note: emulated FPU is a special subcase.  The FPU operations are
heavyweight enough that the overhead of trapping versus library calls is
relatively insignificant.

	-hpa

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