Controlling CPU Allocations in UNIX™ Systems

Abstract

Employing UNIX™ systems' in production environments requires controlling resource allocations so as to achieve service level objectives. For engineering and scientific workloads, these objectives are often expressed as service rates, such as application A should receive 50% of the central processing unit. In most UNIX systems, the only way to control CPU usage is by adjusting nice-values, a per-process (task) tuning knob; unfortunately, the relationship between nice-values and process service rates has been poorly understood. This paper develops an analytic model that relates service rate objectives for compute-bound processes to nice-values and three scheduler parameters: R (the rate at which priority increases for each quantum of CPU consumed), D (the decay factor), and T(the number of quanta that expire before CPU usages are decayed); the model is evaluated using measurements of a workstation running IBM's Advanced Interactive Executive (AIX) 3.1 Operating System. Based on the model, we develop an algorithm for calculating nice-values that achieve service rate objectives for compute-bound processes. Experiments conducted on a production AIX 3.1 system suggest that our algorithm works well in practice.