Messages in this thread | | | Date | Tue, 9 Aug 2011 13:50:50 +0100 | From | Alan Cox <> | Subject | Re: [PATCH v3 0/2] Forcibly enable some MISC_ENABLE features on Intel |
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On Tue, 9 Aug 2011 08:41:04 -0400 Andy Lutomirski <luto@MIT.EDU> 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
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