LITMUS: A Testbed for Empirically Comparing Real-Time Multiprocessor Schedulers. We present a real-time, Linux-based testbed called LITMUS, which we have developed for empirically evaluating multiprocessor real-time scheduling algorithms. We also present the results from such an evaluation, in which partitioned earliest-deadline-first (EDF) scheduling, preemptive and nonpreemptive global EDF scheduling, and two variants of the global PD2 Pfair algorithm were considered. The tested algorithms were compared based on both raw performance and schedulability (with real overheads considered) assuming either hard- or soft-real-time constraints. To our knowledge, this paper is the first attempt by anyone to compare partitioned and global real-time scheduling approaches using empirical data.