Changing the default 32-bit x86 arch for Fedora 12

[Bill Nottingham]

drago01 (drago01 at gmail.com) said: 
> > Way back when in February [1], FESCo decided that for Fedora 11, i586 would
> > be the default architecture, and for Fedora 12, it would be some variant of
> > i686. It's time to follow through on that action item.
> 
> Moving to i686 is fine, non i686 chips are mostly dead (but the
> perfomance gain from moving to i686 from i586 is questionable at
> best).

... how so? It's consistently 1-2% in reasonable benchmarks (real-world
code, albeit cpu-specific).

> This is going to far, it makes x86 no longer useable on anything but
> P4, Pentium M and Atom.
> 
> The only chip which is worth optimizing for is the Atom but its not
> worth killing support for a lot of older systems (ex: Athlon XP system
> are still present and aren't much slower than the non 64bit cable P4)

Well, we could use the Atom tuning support and build with -march=i686
-mtune=atom. That could be fun. 

> > Why?
> >
> > - Faster and more consistent FP math by using SSE2 registers
> 
> Only in certain apps, and most of them have handwritten SSE routines anyway.

-fpmath=sse is faster in general, not just in specifc apps. (According
to all the toolchain people I've talked to.)

Bill