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Re: Changing the default 32-bit x86 arch for Fedora 12



On Mon, Jun 15, 2009 at 7:53 PM, Bill Nottingham<notting redhat com> wrote:
> 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).

> I've submitted https://fedoraproject.org/wiki/Features/F12X86Support. It
> defines the default arch as i686 + SSE2.

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)

> Why?
>
> - Faster and more consistent FP math by using SSE2 registers

Only in certain apps, and most of them have handwritten SSE routines anyway.

> - Allows for autovectorization by GCC where necessary

We don't build with autovectorization anyway (unless we move to -O3
for the default cflags)

> - More clearly delineates our support set of targets, sticking true
>  to forwards innovation, not necessarily legacy support

Yeah that's why we hide the x86_64 arch from the download page and
promote x86 everywhere.(attempt to change this failed)

So to sum it up: I doubt that we gain anything by doing this other
than some frustrated users and maybe higher performance in some micro
benchmarks that are not noticeable in real world apps.


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