Compiling for CPU (was Re: Performance testing (pass 1))

[Elliot Lee]

On Fri, 26 Sep 2003, Rick Johnson wrote:

> One question I've always had is why Red Hat still compiles for i386 
> (march=i386 mcpu=i686 - ok, so they get i686 instruction ordering)? Once 
> upon a time, I rebuilt my entire RH 7.3 tree and a good portion of my RH 
> 8.0 tree for i686 and/or athlon. I've also run Gentoo, compiled for 
> Athlon XP, which isn't as solid of a comparison, but is still a "Linux" 
> general comparison. In both Red Hat cases, there was an appreciable 
> difference, especially in X GUI "redraw" speed and application start 
> times.

The general consensus has been that this is the placebo effect in action.  
Especially given the fact that glibc already has an i686 variant, and that
objective, precise benchmarks are in short supply, it might be valuable to
first answer the question of what performance changes different compiler
options really provide.

-- Elliot
Individualists, unite!