The ES hardware has a 3-level hierarchy of parallelism: vector processing in an AP, parallel processing with shared memory in a PN, and parallel processing among PNs via IN. To bring out high performance of ES fully, you must develop parallel programs that make the most use of such parallelism.

Table 1: Programming Model on ES

As shown in Table 1, the 3-level hierarchy of parallelism of ES can be used in two manners, which are called hybrid and flat parallelization, respectively (Figure 7). In the hybrid parallelization, the inter-node parallelism is expressed by HPF or MPI, and the intra-node by microtasking or OpenMP, and you must, therefore, consider the hierarchical parallelism in writing your programs. In the flat parallelization, the both inter- and intra-node parallelism can be expressed by HPF or MPI, and it is not necessary for you to consider such complicated parallelism. Generally speaking, the hybrid parallelization is superior to the flat in performance and vice versa in ease of programming. Note that the MPI libraries and the HPF runtimes are optimized to perform as well as possible both in the hybrid and flat parallelization.

Figure 7: Two Types of Parallelization of ES