The foreground/background scheduling model for real-time and cloud systems
In real-time systems, the very basic task model assumes every real-time task (process) is either periodic or can be modeled as periodic one (e.g., sporadic servers). A periodic task is generally assigned three properties: period (T), worst case execution time (WCET, or C) and deadline (D). In every period T, the task needs to complete some job before its deadline D. In the worst possible case with all sorts of execution interference (e.g., interrupts, synchronization, cache evictions, memory bus contention), it takes C amount of time to finish the job. In no period would the job execution time exceed C. In normal execution though, the job time is way smaller than C. C <= D, since if the relative deadline D is smaller than C, the task will always fail in the worst case. Notice D can be greater than T, although most scheduling algorithms and analysis methods assume D <= T or just D = T. You can definitely write a web server that handles one request in every period and has D > T...