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P-3PC: A Simple and Accurate Model of Point-to-Point Communication

This report presents the P-3PC model (or the ’Parameterized model based on the Three Paths of Communication’) for predicting the execution time of the standard blocking point-to-point communication operations defined in MPI. In comparison with other models described in the literature (e.g., Postal Model, LogP) P-3PC is similar in complexity, but more accurate. First, P-3PC acknowledges the difference in the time both communicating nodes are occupied in a message transfer, and the complete end-to-end delivery time. Also, it incorporates a possible difference in the communication of data stored either contiguously or noncontiguously in memory. Finally, the model acknowledges that the growth in the cost of communication in relation to the size of a message being transmitted is not necessarily linear. The P-3PC model is applied in the process of automatic optimization of parallel image processing applications. Experimental results show that the model allows accurate evaluation of tree-based collective communication operations implemented using multiple point-to-point operations. As collective operations of this kind are essential in parallel computation, we expect P-3PC to be applicable in many other research areas as well.