x86_64 lacks the _PDC staff, so C2/C3 SMP can't work in x86_64.
Created attachment 6672 [details] patch to invoke _PDC for x86_64
Created attachment 6744 [details] rebased against Venki's _PDC changes
Created attachment 7273 [details] patch against 2.6.16-rc2
applied to acpi-test
shipped in 2.6.17-git9, closed.