[KLUG Members] SMP and ACPI in 2.6.12

[Kevin Mitchell]

I recently upgraded some dual Xeon machines from the 2.6.3 kernel to 
2.6.12 and it appeared to break SMP.  When I would cat /proc/cpuinfo or 
ran top I would only see 2 processors rather than the previous 4 
processors.  After some head scratching and google searches I tried 
enabling ACPI support for Processor and Thermal Zone and recompiled and 
I had my 4 processors again.  It appears that there has been some change 
in the kernel between 2.6.3 and 2.6.12 that makes this necessary.  Does 
anyone know if this is intentional?  Has anyone else ran into such a 
thing?