FC3 and Pentium 4 optimization?

Dave Jones davej at redhat.com
Fri Jan 7 19:46:17 UTC 2005

On Fri, Jan 07, 2005 at 01:21:38PM -0600, Steve Bergman wrote:
 > I am seeking clarification of a point made in the release notes.  It 
 > states that FC3 is optimized for Pentium 4.  However the kernels and 
 > glibc available are labeled as i686 and i386.  I assume, since Pentium 1 
 > is the minimum hardware requirement, that the instruction set used is 
 > Pentium 1.  So:
 > 1. What optimization and instruction set are the general packages 
 > actually compiled with?
 > 2. What optimization and instruction set are glibc-i686 and  kernel-i686 
 > compiled with? (I seem to recall that the kernel is now optimized for size.)
 > 3. How important is this to someone running a different processor? (Say 
 > Athlon XP.) IIRC p4 has very specific optimization requirements.

Currently, the kernel is compiled with -Os (size optimise),
with 686 instructions (so that it runs on early pentiums),
with instruction scheduling tuned for Pentium 4.

In tests I did, -mtune=pentium4 was a win on pretty much everything
I tried. Bizarrely in some cases, it even beat -mtune=athlon-xp
when I ran it on my athlon.  VIA cpus didn't seem to be greatly
affected regardless of what the code was tuned for.


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