Re: MMX performance....

Alan Cox (alan@lxorguk.ukuu.org.uk)
Thu, 6 Feb 1997 22:09:48 +0000 (GMT)

> Is it allowed to use FPU/MXX inside kernel? I recall that this is not
> possible since kernel doesn't save FPU state when swiching between kernel
> and user modes. Or am I just misunderstood this.

You can use FPU/MMX in kernel but you must save the CPU state and restore
it right including coping with the lazy saving, 386 late interrupt stuff,
exception handling from the past state occuring on the FSAVE and SMP
synchronization issues etc.

If you wanted to run one of these idiot new MMX sound cards I suspect
the way to do it would be to run the MMX driver as a kernel thread.

Alan