The compute_reference function explicitly checks if the current
frequency is different from the default one. In that case, it runs a
projection to determine what the runtime and power usage would have
been, if the program was actually running at the default frequency.

If the current frequency is the same as the default one, then the
values from the last signature are returned as is.

By overwriting the current frequency with the default one, the
min_energy policy will always use the values from the last signature
as the reference. This means, that it *cannot* raise the frequency,
since it has to find a frequency that will have a lower power
consumption than the reference.