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SubjectSMT, again (was: Re: [PATCH]: Fix MTRR handling on HT CPUs)

I just found out that Intel specifies that on SMT-enabled
("Jackson") systems the BIOS MP tables list only the physical CPUs.
Logical CPUs will only be available through the ACPI tables.

in particular sld014.htm, sld021.htm.

This will basically obsolete the patch we were discussing, if BIOS
manufacturers comply to that spec, because linux will only see the
2 physical CPUs. (The problem we discovered was caused by our BIOS not
complying to the spec).

Of course, it would also mean that Linux will only run on ~70% of the CPU
power that Win2k/XP systems will have available on such systems.

All my attempts to get ACPI running on our SMT-enabled system have failed
so far (I'm working on a bug report on that for linux-acpi).

A possible workaround would be the "processor affinity algorithm"
sketched in sld021.htm, but it may be unreliable because it overrides
BIOS settings (BIOS-diabled CPUs) that are available only through ACPI.

Sorry to bother if you knew this already.


Martin Wilck Phone: +49 5251 8 15113
Fujitsu Siemens Computers Fax: +49 5251 8 20409
Heinz-Nixdorf-Ring 1
D-33106 Paderborn

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