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Re: i686 build of Fedora Core



Alan Cox wrote:
On Wed, Jul 28, 2004 at 09:50:11PM +0200, Angelo wrote:

Sure, but what can do optimization without using the *hardcoded* cpu
instructions inserted in the architecture ?


90% of the optimisation work is scheduling instructions - picking which one
to use and how to lay them out. The actual instructions added by 486 and
later are not much use. Essentially it adds

	bswap		- 	which nothing uses except kernel net code
	cmov		- 	which is now slower than avoiding it

and a collection of locked operations that are great for threading and
are a big reason glibc has a i686 version since it contains all the pthreads
stuff.


Actually, the big ones are MMX/MMXEXT/SSE-{1,2,3}. In particular sse2, since sse2 can be used for all floating-point (-msse2 -mfpmath=sse), and on some CPUs it can be 2x or more faster than using x87.


-hpa



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