[gentoo-user] mmx use flag on Pentium 4

[gentoo-user] mmx use flag on Pentium 4

[Robert Persson]

Should I enable the mmx use flag when I am compiling stuff (e.g. mplayer) for 
a pentium 4?  I'm confused because I've kind of got the idea that mmx is 
obsolete, but I'm not clear exactly how obsolete.

Many thanks
Robert
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Robert Persson

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Re: [gentoo-user] mmx use flag on Pentium 4

[Jonathan Wright]

Robert Persson wrote:
> Should I enable the mmx use flag when I am compiling stuff (e.g. mplayer) for 
> a pentium 4?  I'm confused because I've kind of got the idea that mmx is 
> obsolete, but I'm not clear exactly how obsolete.

In theory, yes it is sort of obsolete - sse and sse2 are the preferred
method. However, so long as you have specified -march=pentium4 (and
-mcpu=pentium4 or -mtune=pentium4 with >=gcc-3.4) mmx/sse/sse2 will be
implied as part of the compilation process.

As for mplayer - unless you set the appropriate use flag, then almost
all C(XX)FLAGS will be remove from the process as (like gaim) it is
notoriously flaky with anything other than the basic settings.

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Re: [gentoo-user] mmx use flag on Pentium 4

[Walter Dnes]

On Sat, Sep 24, 2005 at 09:45:30PM +0100, Jonathan Wright wrote

> In theory, yes it is sort of obsolete - sse and sse2 are the preferred
> method. However, so long as you have specified -march=pentium4 (and
> -mcpu=pentium4 or -mtune=pentium4 with >=gcc-3.4) mmx/sse/sse2 will be
> implied as part of the compilation process.
> 
> As for mplayer - unless you set the appropriate use flag, then almost
> all C(XX)FLAGS will be remove from the process as (like gaim) it is
> notoriously flaky with anything other than the basic settings.

  I'm running gcc 3.3.6.  I just ran "emerge --sync" a few minutes ago.
Running "emerge --ask --deep --update --world" doesn't mention gcc.  Are
you unmasking a test version?

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My musings on technology and security at http://tech_sec.blog.ca
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Re: [gentoo-user] mmx use flag on Pentium 4

[Jonathan Wright]

Walter Dnes wrote:
>   I'm running gcc 3.3.6.  I just ran "emerge --sync" a few minutes ago.
> Running "emerge --ask --deep --update --world" doesn't mention gcc.  Are
> you unmasking a test version?

I think gcc-3.4* is still marked ~x86; however since that version -mcpu 
has been depreciated in favor for -mtune.

As for the mmx information, that's valid across all gcc versions. If you 
specify -march=pentium4 and -mcpu=pentium4 as part of your CFLAGS, -mmmx 
and -msse, etc., will be implied by the compiler, and any programs built 
to take advantage of the extensions will be able to do so.

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Re: [gentoo-user] mmx use flag on Pentium 4

[Walter Dnes]

On Sat, Sep 24, 2005 at 11:10:35PM +0100, Jonathan Wright wrote

> however since that version -mcpu has been depreciated in favor for -mtune.

  I use -march, so that point is moot.

> As for the mmx information, that's valid across all gcc versions. If
> you specify -march=pentium4 and -mcpu=pentium4 as part of your
> CFLAGS, -mmmx and -msse, etc., will be implied by the compiler,
> and any programs built to take advantage of the extensions will be
> able to do so.

  The docs for 3.4.X are a lot more detailed than 3.3.X docs.  3.3.6
docs say that -march implies -mcpu but don't say in so many words that
certain values of -march imply -sse, etc.

  While we're talking about compilers and sparse documentation, I've got
an AMD64 K8.  The docs for an AMD64-bit install scared me off to 32-bit
land.  Later I found out that the 64-bit install docs are out-of-date
and the problems they mention seem to have been solved.  However, since
I have things humming along, I don't really want to tear my install down
and rebuild from scratch.  One question... I'm running
> CFLAGS="-O2 -pipe -fomit-frame-pointer -march=athlon -m3dnow -mmmx -msse -msse2 -mfpmath=sse"

  Is there a way to figure out if I can use a higher version of Athlon
in my CFLAGS line in 32-bit mode?

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