Disabling FPU, MMX, SSE units?

Disabling FPU, MMX, SSE units?

[Pavel Machek]

Hi!

Is there way not to let linux use FPU, MMX, SSE and similar fancy
units? I have athlon processor, but would like to turn FPU (and
similar fancy stuff) off...
							Pavel
PS: I'm trying to narrow down sigsegv-after-resume problem... Getting
rid of fancy 486+ features would help me.
-- 
<sig in construction>

Re: Disabling FPU, MMX, SSE units?

[Maciej W. Rozycki]

On Wed, 21 Nov 2001, Pavel Machek wrote:

> Is there way not to let linux use FPU, MMX, SSE and similar fancy
> units? I have athlon processor, but would like to turn FPU (and
> similar fancy stuff) off...

 You may use "no387" to disable FPU and MMX (they are controlled by a
single bit in cr0).  No idea about SSE.

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +

Re: Disabling FPU, MMX, SSE units?

[Rasmus Bøg Hansen]

On Thu, 22 Nov 2001, Maciej W. Rozycki wrote:

> On Wed, 21 Nov 2001, Pavel Machek wrote:
> 
> > Is there way not to let linux use FPU, MMX, SSE and similar fancy
> > units? I have athlon processor, but would like to turn FPU (and
> > similar fancy stuff) off...
> 
>  You may use "no387" to disable FPU and MMX (they are controlled by a
> single bit in cr0).  No idea about SSE.

Running a kernel optimized for 386 should leave out MMX, SSE and similar 
fancy instrucion sets IIRC.

Rasmus

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--------------------------------- [ moffe at amagerkollegiet dot dk ] --

Re: Disabling FPU, MMX, SSE units?

[Randy.Dunlap]

"Maciej W. Rozycki" wrote:
> 
> On Wed, 21 Nov 2001, Pavel Machek wrote:
> 
> > Is there way not to let linux use FPU, MMX, SSE and similar fancy
> > units? I have athlon processor, but would like to turn FPU (and
> > similar fancy stuff) off...
> 
>  You may use "no387" to disable FPU and MMX (they are controlled by a
> single bit in cr0).  No idea about SSE.

Looks to me like another candidate for the setup/bugs/cpuid
processor-type splitting/cleanup that DaveJ et al have mentioned
[for 2.5 ?].

include/asm-i386/bugs.h is the only header file in linux/ that
contains^W hides __setup() parameters, and that's bad IMO.

~Randy

Re: Disabling FPU, MMX, SSE units?

[Zwane Mwaikambo]

You can't disable MMX/SSE because its used to optimise, if you don't want
to use SSE/MMX select a non-SSE/MMX cpu in the kernel config, that way
you'll lose those assembly optimisations. If you want to impare your CPU
even more (as seems the case) consider using 486 as a CPU target and perhaps also
cripple your cpu caches (ie set bit 0x1E (CD) in cr0).


Cheers,
	Zwane Mwaikambo