WAP: Unreasonable distributions of execution time under reasonable conditions

Reliability and safety often depend on the execution times of software tasks being reasonably consistent and predictable if not strictly bounded in the real-time sense. Since commodity computers are theoretically deterministic machines, one might expect the elapsed and CPU time required to execute a fully-defined, deterministic software task with no complications to satisfy that requirement. But experiments at NIST have produced distributions of elapsed and CPU time which are "unreasonable" enough to invalidate the statistical assumptions and confidence intervals that are ordinarily used to summarize results. If this variability is endemic to the modern hardware and operating systems that are deployed, then increasingly invasive methods of controlling it in the lab are of marginal interest. Instead, it needs to be characterized and dealt with. Some approaches are suggested with the aim of starting a discussion.