Soft Real-Time on Multiprocessors: Are Analysis-Based Schedulers Really Worth It?

The evolution of multicore platforms has led to much recent work on multiprocessor scheduling techniques for soft real-time workloads. However, end users routinely run such workloads atop general-purpose operating systems with seemingly good results, albeit typically on over-provisioned systems. This raises the question: when, if ever, is the use of an analysis-based scheduler actually warranted? In this paper, this question is addressed via a video-decoding case study in which a scheme based on the global earliest-deadline-first (GEDF) algorithm was compared against Linux's CFS scheduler. In this study, the GEDF-based scheme proved to be superior under heavy workloads in terms of several timing metrics, including jitter and deadline tardiness. Prior to discussing these results, an explanation of how existing GEDF-related scheduling theory was applied to provision the studied system is given and various "mismatches" between theoretical assumptions and practice that were faced are discussed.