At the top level of the POP hierarchy we can find the Global Efficiency (GE). It measures the overall quality of the parallelisation.
Typically, inefficiencies in parallel code have two main sources: 1) overheads imposed by the parallel nature of a code (i.e., the Parallel Efficiency); and 2) poor scaling of computation with increasing numbers of processes (i.e., the Computation Efficiency). The Global Efficiency metric is the product of these two sub-metrics:
GE = Parallel Efficiency * Computation Efficiency