Mallach, E. G. | Search NASA

NASA NTRS1976

Simulating an aerospace multiprocessor

The paper describes a simulator which was used to evaluate the architecture of an aerospace multiprocessor. The simulator models interactions among the processors, memories, the central data bus, and a possible 'job stack'. Special features of the simulator are discussed, including the use of explicitly coded and individually distinguishable 'job models' instead of a statistically defined 'job mix' and a specialized Job Model Definition Language to automate the detailed coding of the models. Some results are presented which show that when the simulator was employed in conjunction with queuing theory and Markov-process analysis, more insight into system behavior was obtained than would have been with any one technique alone.

Mallach, E. G.↗

NASA NTRS1972

Job-mix modeling and system analysis of an aerospace multiprocessor.

An aerospace guidance computer organization, consisting of multiple processors and memory units attached to a central time-multiplexed data bus, is described. A job mix for this type of computer is obtained by analysis of Apollo mission programs. Multiprocessor performance is then analyzed using: 1) queuing theory, under certain 'limiting case' assumptions; 2) Markov process methods; and 3) system simulation. Results of the analyses indicate: 1) Markov process analysis is a useful and efficient predictor of simulation results; 2) efficient job execution is not seriously impaired even when the system is so overloaded that new jobs are inordinately delayed in starting; 3) job scheduling is significant in determining system performance; and 4) a system having many slow processors may or may not perform better than a system of equal power having few fast processors, but will not perform significantly worse.

Mallach, E. G.↗