DISABLE CPU CORES

AMD's 12-core "Magny-Cours" Opteron 6174 / BL 465 G7
1) BIOS - System Options --> Processor Options---> Processor Core Disable/AMD Core Select
Note : Value entered is number of cores enabled per socket. Valid entries are even core counts.

2) Edit grub
http://en.kioskea.net/faq/616-multicore-cpu-how-to-disable-a-core#procedure-when-using-linux
kernel /boot/vmlinuz-2.6.22-14-generic root=UUID=a8a39729-9d2a-425b-b84b-ecc5c7dad104 ro quiet maxcpus=2

3) Dynamically enable and disable processor core
http://www.cyberciti.biz/faq/debian-rhel-centos-redhat-suse-hotplug-cpu

# echo 0 > /sys/devices/system/cpu/cpu6/online [Disabled]
# echo 1 > /sys/devices/system/cpu/cpu6/online [Enabled]