POLY3 assesses the severity of the communication bottleneck. It is the same as the POLY1 benchmark except that the data for the polynomial evaluation is stored on a neighbouring processor. The value of \fhalf obtained therefore measures the ratio of arithmetic to communication performance. Equation (3) shows that the computational intensity of the calculation must be significantly greater than \fhalf (say 4 times greater) if communication is not to be a bottleneck. In this case the computational intensity is the ratio of arithmetic performed on a processor to words transferred to/from it over communication links. In the common case that the amount of arithmetic is proportional to the volume of a region, and the data communicated is proportional to the surface of the region, the computational intensity is increased as the size of the region (or granularity of the decomposition) is increased. Then the \fhalf obtained from this benchmark is directly related to the granularity that is required to make communication time unimportant.
POLY3 is a new benchmark written specifically for PARKBENCH .