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Computation 2016, 4(4), 41;

Evaluation of External Memory Access Performance on a High-End FPGA Hybrid Computer

School of Electrical and Computer Engineering, Technical University of Crete, Chania 731 00, Greece
Author to whom correspondence should be addressed.
Academic Editor: Harald Köstler
Received: 6 June 2016 / Revised: 9 September 2016 / Accepted: 11 October 2016 / Published: 25 October 2016
(This article belongs to the Special Issue High Performance Computing (HPC) Software Design)
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The motivation of this research was to evaluate the main memory performance of a hybrid super computer such as the Convey HC-x, and ascertain how the controller performs in several access scenarios, vis-à-vis hand-coded memory prefetches. Such memory patterns are very useful in stencil computations. The theoretical bandwidth of the memory of the Convey is compared with the results of our measurements. The accurate study of the memory subsystem is particularly useful for users when they are developing their application-specific personality. Experiments were performed to measure the bandwidth between the coprocessor and the memory subsystem. The experiments aimed mainly at measuring the reading access speed of the memory from Application Engines (FPGAs). Different ways of accessing data were used in order to find the most efficient way to access memory. This way was proposed for future work in the Convey HC-x. When performing a series of accesses to memory, non-uniform latencies occur. The Memory Controller of the Convey HC-x in the coprocessor attempts to cover this latency. We measure memory efficiency as a ratio of the number of memory accesses and the number of execution cycles. The result of this measurement converges to one in most cases. In addition, we performed experiments with hand-coded memory accesses. The analysis of the experimental results shows how the memory subsystem and Memory Controllers work. From this work we conclude that the memory controllers do an excellent job, largely because (transparently to the user) they seem to cache large amounts of data, and hence hand-coding is not needed in most situations. View Full-Text
Keywords: High Performance Reconfigurable Computer (HPRC); Convey HC-2x; Convey HC-2x bandwidth; memory management High Performance Reconfigurable Computer (HPRC); Convey HC-2x; Convey HC-2x bandwidth; memory management

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Kalaitzis, K.; Sotiriadis, E.; Papaefstathiou, I.; Dollas, A. Evaluation of External Memory Access Performance on a High-End FPGA Hybrid Computer. Computation 2016, 4, 41.

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