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Date: Tue, 10 Nov 2009 21:54:45 +0100 From: Pavel Machek <pavel@....cz> To: Willy Tarreau <w@....eu> Cc: "H. Peter Anvin" <hpa@...or.com>, 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 Hi! > 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 Well, fix the distros... > 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. > > One could argue that cmpxchg/bswap/xadd are supported by 486 and that > implementing them for 386 is almost useless now (though it costs almost > nothing to provide them, I did a few years ago). > > CMOV/NOPL are rarely used, thus have no reason to cause a massive > performance drop, but are frequent enough (at least cmov) for almost *One* CMOV in the inner loop will make your performance go down 20x. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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