On Tue,  9 Aug 2011 08:41:04 -0400
Andy Lutomirski [off-list ref] wrote:

Intel allows BIOS or the OS to enable or disable some CPU fueatures via
IA32_MISC_ENABLE.  I have machines that don't enable fast strings or
monitor/mwait in BIOS, so do it on bootup instead.

The question is - why. 

The Intel SDM volume 3, appendix B.1 says that the OS should not touch
the monitor enable bit if SSE3 is not present, which presumably means
that the OS may touch that bit if SSE3 is present.  In any case, these
patches seem to work.

That's a big "presumes"

For example back in Pentium days the BIOS sometimes turned off a string
fast path because it was subtly not reliable on certain parts and could
corrupt.

It's possible your BIOS vendor has a good reason for doing this. It's
also possible its a bug, or a left over perhaps from some pre-release
processor or something.

I think a bit more research is probably appropriate before processor
configuration hacks go in that 'seem to work'.

Alan