CPU Frequency scaling allows you to change the clock speed of
CPUs on the fly. This is a nice method to save power, because
the lower the CPU clock speed, the less power the CPU consumes.

Note that this driver doesn't automatically change the CPU
clock speed, you need to either enable a dynamic cpufreq governor
(see below) after boot, or use a userspace tool.

For details, take a look at Documentation/cpu-freq.

If in doubt, say N.

source code:

drivers/cpufreq/