Opportunity Scheduling: An Unfair CPU Scheduler for UNICOS
Richard Klamann · 1997
Fair Share is the standard scheduling algorithm used for political resource control on large, multi-user UNIX systems. Promising equity, Fair Share has instead delivered frustration to its Los Alamos UNICOS users, who perceive misallocations of interactive response within a system of unreasonable complexity. This paper reviews the design of the Kay/Lauder Fair Share system, as well as its Cray UNICOS implementation, and concludes that the underlying model is inappropriate for interactive control. A new resource manager, Opportunity Scheduling, is then presented. Salient features of the new scheduler include: (1) direct management of interactivity (or “computing opportunity”), (2) job prioritization within resource groups, (3) cooperative memory scheduling, and (4) a simple, user-oriented interface. The paper then contrasts Opportunity Scheduling with the batch system employed at Los Alamos, where throughput and cycle allocation, rather than computing opportunity, are paramount considerations. It concludes with anecdotal experiences under the system.