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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.

See http://www.intel.com/technology/hyperthread/platform_nexgen/,
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

--
Martin Wilck Phone: +49 5251 8 15113
Fujitsu Siemens Computers Fax: +49 5251 8 20409
Heinz-Nixdorf-Ring 1 mailto:Martin.Wilck@Fujitsu-Siemens.com
D-33106 Paderborn http://www.fujitsu-siemens.com/primergy





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