Never had anyone ask this one before
I will have to do some checking on this.
Why do yo want to shut one down? System too fast?
There is an option in BIOS set up under the Advance Processor to select the number of multi-cores from ALL down to 1, but no way to turn on a CPU package completly.
You can also use node manager to set limits on the system total power draw which can throttle the processors and reduce power comsumption.