Re: [gentoo-user] USE="mmx mmxext sse sse2 ssse3 3dnow 3dnowext"

[Volker Armin Hemmann <volkerarmin@googlemail.com>]

On Dienstag 26 Mai 2009, Stroller wrote:
> Hi there,
>
> I'm always rather reluctant to enable any of these, being unsure
> whether my ageing PentiumPro or Pentium 4 CPUs support such features
> as 3DNow! (originally an AMD technology) or the advanced SSSSSSSSSE3.
>
> According to this page <http://en.gentoo-wiki.com/wiki/MPlayer>,
> however:
>
>     You can greatly improve MPlayer's performances (in my experience, by
>     up to +40%!) by recompiling it with appropriate CPU-related USE
> flags.
>
> Moreover:
>
>     Note: The mplayer build system will automatically detect your CPU
>     settings if you allow it. Therefore, the safest thing to do is
> enable
>     all of the optimization USE flags and let the script detect them. If
>     you disable the use flags, then it will forcibly disable support for
>     that optimization, and possibly break your build. In other words,
> add
>     mmx mmxext sse sse2 ssse3 3dnow 3dnowext to your USE flags for this
>     ebuild, and if your box supports it, it will work automatically.
>
> w00t!
>
> Should I enable all these USE flags globally? Will other packages also
> fallback safely as mplayer does?
>
> Or should I add all these flags only to /etc/portage/package.use,
> allowing mplayer to make full use of the hardware USEs it supports,
> but limiting other apps to only those I'm really really confident
> about (i.e. "mmx" & that's about it).
>
> Thanks in advance for all suggestions,
>
> Stroller.

you can enable them globaly.

If a package would build using say 3dnow without the cpu supporting it it will 
crash with an instruction error. So either it works always or never.

Just look at /proc/cpuinfo you find everything you need to know there. It 
isn't hard. In fact, it is really ,really simple.