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    SubjectRe: i686 quirk for AMD Geode
    On Tue, Nov 10, 2009 at 12:25:02PM -0800, H. Peter Anvin wrote:
    > On 11/10/2009 12:16 PM, Willy Tarreau wrote:
    > >
    > > Indeed, but there is a difference between [cmpxchg, bswap, cmov, nopl]
    > > on one side and [sse*] on the other : distros are built assuming the
    > > former are always available while they are not always. And the distro
    > > which make the difference have to provide an dedicated build for earlier
    > > systems just for compatibility. SSE*, 3dnow* etc... are only used by a
    > > handful of media players/converters/encoders which are able to detect
    > > themselves what to use and already have the necessary fallbacks because
    > > these instruction sets vary too much between processors and vendors.
    > >
    > That is increasingly not true since gcc is now doing autovectorization.

    But programs have to be built to use that specific platform anyway ; this
    is different from all programs built with support for CMOV enabled by
    default and which will work on 95% of the platforms.

    > I could 970 cmovs in libc out of 322660 instructions. That is one in
    > 333 instruction.

    Not bad, I agree ! But on the C3, CMOV from/to register is implemented.
    It's only CMOV from/to memory which has to be emulated, which makes it
    a lot less common. Anyway that's why we need counters, so that the user
    knows when he really ought to recompile.

    > I don't see any particular subset as being more obvious than the other,
    > with the *possible* exception of NOPL, simply because NOPL was
    > undocumented for so long.

    well, simply the availability of binaries making use of them. I'm not
    sure you would find SSE* instructions in your libc where you found the
    970 cmov. For NOPL, that's different, I first heard about it in this
    thread, and my C3 running with the CMOV patch has never complained from
    missing it :-)


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