Overclocking the processor — running it above its specified maximum
frequency to increase performance — is a familiar operation for many
readers. Sometimes, however, it is necessary to go the other direction and
decrease a processor’s operating power point by lowering its voltage
to avoid overheating. Recently, Jason Donenfeld submitted a short
patch removing a warning emitted by the kernel when user space accesses
special processor registers that allow this “undervolting” on x86
processors. It caused a long discussion that might result in a kernel
interface to allow users to safely control their processor’s voltage.

Source: LWN.net – [$] Kernel support for processor undervolting