The elusive goal of workload characterization.

The study and design of computer systems requires good models of the workload to which these systems are subjected. Until recently, the data necessary to build these models---observations from production installations---were not available, especially for parallel computers. Instead, most models were based on assumptions and mathematical attributes that facilitate analysis. Recently a number of supercomputer sites have made accounting data available that make it possible to build realistic workload models. It is not clear, however, how to generalize from specific observations to an abstract model of the workload. This paper presents observations of workloads from several parallel supercomputers and discusses modeling issues that have caused problems for researchers in this area.