Effectiveness of combining in shared memory parallel computers in the presence of 'hot spot'

Technical Report · Wed Jan 01 04:00:00 EST 1986

OSTI ID:7258117

Lee, G; Kruskal, C P; Kuck, D J

Concurrent requests to a shared variable by many processors on a shared memory machine obviously create contention, which seems to become serious enough to stall the whole machine as the machine size grows. To alleviate the contention, restricted combining, in which two requests can be combined into a single request at a 2 x 2 switch, was suggested for the NYU Ultracomputer. We study the effectiveness of combining by considering several schemes under the nonuniform traffic model used by Pfister and Norton. Although restricted combining has been claimed as an effective way of allowing concurrent requests, in practice we witness a serious contention that can cripple the performance if the machine size is ''large''. Restricted combining seems to be too severe a restriction. The number of requests that can be combined at a switch turns out to be an important factor in the effectiveness of combining. Even a ''slight'' increase in the number of requests combined at a switch can resolve the problem. 15 refs., 5 figs.

• Research Organization: Illinois Univ., Urbana (USA). Center for Supercomputing Research and Development; Maryland Univ., College Park (USA). Dept. of Computer Science
• DOE Contract Number: FG02-85ER25001
• OSTI ID: 7258117
• Report Number(s): DOE/ER/25001-22; CSRD-547; ON: DE87002118
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS
990200* -- Mathematics & Computers
COMPUTERS
DIGITAL COMPUTERS
MEMORY DEVICES
PARALLEL PROCESSING
PROGRAMMING
SUPERCOMPUTERS