Communication Efficiency (CommE) is the maximum across all processes of the ratio between useful computation time and total run-time:

CommE = maximum computation time / total run-time

CommE identifies when code is inefficient because it spends a large amount of time communicating rather than performing useful computations. CommE is composed of two additional metrics that reflect two causes of excessive time within communication:

• Processes waiting at communication points for other processes to arrive (i.e. serialization)
• Processes transferring large amounts of data relative to the network capacity

These are measured using Serialization Efficiency and Transfer Efficiency. In obtaining these two sub-metrics we first calculate (using the Dimemas simulator) how the code would behave if run on an idealized network where transmission of data takes zero time.

These two sub-metrics combine to give Communication Efficiency:

CommE = Serialization Efficiency * Transfer Efficiency