Red Hat Knowledgebase: How do I determine if my x86-compatible Intel system is multi-processor, multi-core or supports hyperthreading?
CPU Identifications in linux kernels (2.6.18 + rhel patches) , NOTE that this is not applicable when you are running linux kernel on top of virtual hardware (i.e. Dom0 and DomU kernels won't show proper CPU info because they use "virtual CPU" as set by XEN )