I have na gigabyte 990FXA-UD3 and for me the CPU CORE CONTROL function works to Disable cores. FX x3xx cpus are assembled in 1 module 2 cores. That function can be used to disable cores, for exemple a FX 8320 that has 4modules 8cores can be turned into a 4 core 4 module chip similar to an intel i5. the 1-2-3-4 is the cores that you can disable leaving core 5-6-7-8 enabled.
you can also use this function to enable the 2 cores hidden in your CPU transforming into an 8core chip. but this is not recommended, theyr are locked cause of instability/malfunction.
You just need to load the defaulf settings, and dont need to do anything else, the mobo bios will do all the rest