Re: [gentoo-dev] make.conf optimization flags for k6, athlon

[Dan Armak]

On Friday 13 July 2001 23:54, you wrote:
> On Fri, Jul 13, 2001 at 11:35:05PM +0300, Dan Armak wrote:
> > Hi all,
> >
> > In make.conf we specify the optimization CXXFLAGS as follows:
> >
> > # For Pentium and k6/2 machines
> > # -----------------------------
> >
> > #CHOST="i586-pc-linux-gnu"
> > #CFLAGS="-mpentium -march=pentium -O3 -pipe"
> > #CXXFLAGS="-mpentium -march=pentium -O3 -pipe"
> >
> > Why don't we use -march=k6 -mcpu=k6? Wouldn't that allow use of mmx and
> > 3dnow, which a generic pentium doesn't have?
>
> -march=k6 will cause the i586 build to *not* run on a Pentium Classic or
> MMX, which is why we don't use it.  However, just the -mcpu=k6 should work
> on anything.

I understand that, it reinforces what I said. People who compile from build 
snapshots should set more 'exact' optimization settings, and make.conf's 
comments should tell them to do so.

For example: I have a k6-2/500. When I first built Gentoo on top of a build 
snapshot, I used the make.conf instructions and now hae a system optimized 
for a generic pentium (i.e. it doesn't even use MMX). I'm not going to 
generate binary tarballs for use on other machines, so I'll now change my 
make.conf settings to have -march-k6 -mcpu=k6 and recompile all my packages 
for better performance. Doesn't that make sense?

make.conf should tell people this: i.e. that they can compile with better 
optimization but lose the ability to run the resulting executable on inferior 
CPUs.


Dan Armak