LinuxSA Mailing list archives

  From: Andreja Zivkovic <andy@zt.zivkotech.net.au>
  To  : linuxsa@linuxsa.org.au
  Date: Sat, 15 Jan 2000 12:48:16 +1030

making a faster system

A thread similar to this was around before, but I don't keep every message
posted, and I couldn't find it in the archives (mainly because they're
grouped in months, and I don't know which month of which year the thread was
in).

Anyway, I recently decided I needed something interesting to do, so I
thought, why use binaries made for a i386 (I use RedHat 6.1), when I have a
PII? I decided to go straight into trying this, before finding out how to
really achieve this. Firstly, I'd like advice on how to do it, and if what I
already tried is good enough, then why I couldn't get glibc to compile.

Firstly, I'd like some advice. I like RPMs a lot. It lets me
uninstall/upgrade packages without me having to keep a log for each package,
trying to remember where every file it contains was installed. Some
programs' Makefile lets you do a 'make uninstall', but not all do, and in
the past, I haven't kept the source for what I've used. Also, I don't know
how to write rpm spec files (looking through them, it doesn't look too hard,
but the major problem, in my opinion, is that I'd have to separately compile
the program, find every file the program uses, then use that info to build
the spec file, so I can compile it again).

What I tried was copy /usr/lib/rpm/rpmrc to /root/.rpmrc and add the line
'optflags:
i686 -O5 -ffast-math -funroll-loops -fomit-frame-pointer -march=pentiumpro -
mcpu=pentiumpro'
(it's on the same line in the file, but I'm sure that the above line will be
cut at around 80 characters).
and I used 'rpm --rebuild --target=i686 <rpm source>' to build it. Compiling
some programs (ypbind comes to mind), these flags were used, so I figure,
they should be built for a i686 CPU and optimised.

Is this the right way to make optimised programs for the i686, or do I need
to get PentiumGCC and use that? Since PentiumGCC is a patch to GCC, I think
I should be able to use the egcs source rpm to make a PentiumGCC rpm. Will
that work? :)

If what I'm doing is good enough, why can't I compile glibc? First of all,
it ignored the compiler flags I defined in .rpmrc, and secondly when it runs
the configure script, it complains that my kernel headers are too old. It
needs kernel headers >= 2.0.10, but RH6.1 comes with kernel 2.2.12 (yes, the
kernel-headers was installed, and I even installed kernel-source). I even
tried using the headers from linux-2.3.33, and I got the same error (headers
too old). This only happened if I gave rpm the --target i686 argument. If I
didn't do that, configure would work, but it would set the build platform as
i386-redhat-linux-gnu, instead of i686-redhat-linux-gnu. If I manually ran
the configure script with the same arguments as rpm tried, it worked, but I
didn't set the same shell variables (CCFLAGS, etc).

does compiling things like glibc (and other libraries) and egcs with
optimisation flags actually help, or should I only bother optimising the
'end' applications?

Finally, does anyone know if I rebuild every package for the i686 and make a
CD with a i686 directory instead of the i386, will the install program
automagically work?

thanks in advance for all the help,
Andy