Re: [gentoo-user] cpu flags / USE flags / compiler flags

[waltdnes@waltdnes.org]

On Wed, Aug 31, 2005 at 09:04:21AM -0700, Mark Knecht wrote

> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid
> xtpr
  [...deletia...]
> I then looked for CPU flags that had an equivalent USE flag and that
> might be of use for faster graphics. On this machine I chose mmx, sse
> & sse2. Armed with that I changed my make.conf file to look like this:

  There are CPU flags and there are USE flags.  Some of them have the
same names, and that may confuse you.  It works like this...
  1) Get a listing of your cpu's flags in /proc/cpuinfo
  2) Check against the list of supported flags in gcc for you cpu, and
     add them to CFLAGS
  3) Check http://www.gentoo.org/dyn/use-index.xml for a list of valid
     USE flags, and include any that show up in /proc/cpuinfo
  4) Repeat step 3) with /usr/portage/profiles/use.local.desc for any
     programs you're emerging.  There doesn't seem to be anything
     special on your pentium4, but my AMD64 not only has mmx and 3dnow,
     it also has mmxext and 3dnowext.  mplayer can take advantage of
     them.  I include them in the /etc/portage/package.use entry for
     media-video/mplayer.

 I'll assume that you're using gcc 3.3.5.  In that case, the place to
look for CPU flag options is...

http://gcc.gnu.org/onlinedocs/gcc-3.3.5/gcc/i386-and-x86_002d64-Options.html#i386-and-x86_002d64-Options

  That list shows pentium4, mmx, sse, and sse2.  Also, if you have *ANY*
version of sse available, you can improve performance by running floating
point math via sse, rather than 387 instructions.  I recommend...

CFLAGS="-O2 -pipe -fomit-frame-pointer -march=pentium4 -mmmx -msse -msse2 -mfpmath=sse"

http://www.gentoo.org/dyn/use-index.xml shows mmx and sse as valid USE
flags, so you can include them in USE.

-- 
Walter Dnes <waltdnes@waltdnes.org>
My musings on technology and security at http://tech_sec.blog.ca
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