From: Johnny Hughes mailing-lists@hughesjr.com

All of that is probably true ... but the optimizations are already set by default by the config.guess and autoconf and automake for almost all RedHat SRPMS ... and CentOS doesn't change those, unless absolutely necessary.

Which is what I agree is most preferrable.

Therefore, for almost all packages on CentOS-3 they are --march=i386 --mtune=i686 ...

Maybe I need to look a bit deeper then. I could have swore I've seen many packages with Makefiles (after any autoconf) that clearly send to stdout a "gcc ... --march=i486". Maybe I'm thinking too much of just the kernel itself.

and for most CentOS-4 packages they are --march=i386 -- mtune=pentium4 ... being that the default target is i386.

Yep, I guess the --mtune=pentium4 was introduced with FC2+. I would recommend Intel backtrack though, because it's not the most ideal for other i686 architectures (only true P4 or Athlon). Although the performance hit is not that much.

-- Bryan J. Smith mailto:b.j.smith@ieee.org