Abstract
The Gemini interconnect on the Cray XE6 platform provides for lightweight remote direct memory access (RDMA) between nodes, which is useful for implementing partitioned global address space languages like UPC and Co-Array Fortran. In this paper, we perform a study of Gemini performance using a set of communication microbenchmarks and compare the performance of one-sided communication in PGAS languages with two-sided MPI. Our results demonstrate the performance benefits of the PGAS model on Gemini hardware, showing in what circumstances and by how much one-sided communication outperforms two-sided in terms of messaging rate, aggregate bandwidth, and computation and communication overlap capability. For example, for 8-byte and 2KB messages the one-sided messaging rate is 5 and 10 times greater respectively than the two-sided one. The study also reveals important information about how to optimize one-sided Gemini communication.
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