linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <20091110222756.GF15159@caffeine.csclub.uwaterloo.ca>
Date:	Tue, 10 Nov 2009 22:27:56 +0000
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Willy Tarreau <w@....eu>, 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 Tue, Nov 10, 2009 at 01:19:30PM -0800, H. Peter Anvin wrote:
> 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.

That doesn't seem to be the experience of the arm EABI versus the old
arm ABI with kernel FPU emulation.  Using user space library calls for
FPU is vastly faster than the trapping and kernel FPU emulation.

-- 
Len Sorensen
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