Re: Linux support for Intel MMX CPU's

Malcolm Beattie (
20 Aug 1996 09:35:11 GMT

In article <>,
=?ISO-8859-1?Q?Johan_Myr=E9en?= <> wrote:
>On Fri, 16 Aug 1996, Michael Mansour wrote:
>> During 1997, MMX will be released by Intel with their CPU's, I am
>> wondering whether Linux will be able to take advantage of these advanced
>> multimedia capabilities at chip level? Will it be kernel support or app
>> support or both?
>The kernel itself does not need multimedia capabilities, but I'm sure some
>kernel hacker with a sufficiently twisted mind (especially Linus himself)
>can come up with some interesting uses for the new instructions in the
>kernel code :-)
>Other than that, MMX is purely a user level thing. Applications can start
>using the new instructions and be happy. No kernel support is needed
>(except perhaps for /proc/cpuinfo). The MMX registers map to the FPU
>registers, so no new registers need to be saved on context switch.

Linus mentioned that task switching used tricks to be lazy about
FPU state saving. I can't find the relevant code right now. Maybe
somebody should check that these MMX instructions don't bypass
whatever method Linux uses to trigger a forced save of FPU state.


Malcolm Beattie <>
Oxford University Computing Services
"Widget. It's got a widget. A lovely widget. A widget it has got." --Jack Dee