Interprocessor Memory Access Arbitrating Scheme for TCMP Type Vector Supercomputer

Tadayuki SAKAKIBARA  Katsuyoshi KITAI  Tadaaki ISOBE  Shigeko YAZAWA  Teruo TANAKA  Yoshiko TAMAKI  Yasuhiro INAGAMI  

IEICE TRANSACTIONS on Information and Systems   Vol.E80-D   No.9   pp.925-932
Publication Date: 1997/09/25
Online ISSN: 
Print ISSN: 0916-8532
Type of Manuscript: Special Section PAPER (Special Issue on Architectures, Algorithms and Networks for Massively Parallel Computing)
Category: Computer Architecture
supercomputer,  vector processor,  TCMP,  arbitrate,  interprocessor memory access conflict,  

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We propose an instruction-based variable priority scheme (IBVPS) which achieves high sustained memory throughput on a TCMP type vector supercomputer. Generally, there are two approaches to arbitrating interprocessor memory access conflict: request level priority control and fixed priority control. Each approach, however, affects performance in its own way: In the case of request level priority control, mutual obstruction causes a performance degradation, and in the case of fixed priority control, memory bank monopoly causes a performance degradation. Mutual obstruction refers to the interference among access requests coming from different instructions; memory bank monopoly refers to the un-interrupted accessing of the same memory bank by a series of higher priority instructions. The strategy of the instruction-based variable priority scheme consists in: (a) generally changing the priority assignment of all load/store pipelines at the end of any instruction running in the system, and (b) changing the priority assignment of all load/store pipelines more than once in the middle of an access instruction with a stride greater than 1 or an indirect access instruction which may monopolize some memory banks for an extended period of time. This strategy reduces mutual obstruction because the priority assignment is reshuffled for the entire group of load/store pipelines at a time. it also reduces memory bank monopoly because the opportunity for memory access is made equal among different instructions by changing the priority assignment at the end of an instruction. Moreover, it prevents the memory bank monopoly by a memory access instruction with a stride greater than 1 or an indirect access instruction, by changing the priority assignment more frequently. Consequently, high sustained memory throughput is achieved on TCMP type vector supercomputers.