MPI Communication Efficiency

MPI Communication Efficiency (CommE) can be evaluated directly by following formula:

$\begin{eqnarray*}CommE=\frac{max(time\; in\; OpenMP + serial\; computation\; time) }{max(runtime)} \end{eqnarray*}$

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. serialisation)
Processes transferring large amounts of data relative to the network capacity

These are measured using Serialisation Efficiency and Transfer Efficiency. Combination of these two sub-metrics gives us Communication Efficiency:

CommE = Serialisation Efficiency ⋅ Transfer Efficiency

To obtain these two sub-metrics we need to perform Scalasca trace analysis which identifies serialisations and inefficient communication patterns.