Towards Multi-Policy Hierarchical Scheduling in Linux for Containerized Space Applications

This paper examines the challenges of running containerized flight software on Linux for space systems, focusing on how to achieve both predictability and flexibility in scheduling. While containers provide lightweight isolation, they complicate the temporal determinism required by safety-critical spacecraft. Hierarchical scheduling and support for multiple policies are increasingly necessary to accommodate heterogeneous onboard workloads, from hard real-time control loops to best-effort processing. To address these challenges, a methodology is introduced for designing, analyzing, and implementing hierarchical multi-policy scheduling on Linux. The approach is structured around a meta-model capturing the key concepts of hierarchical reservation, a formal analysis based on the Compositional Scheduling Framework (CSF) for sizing container budgets, and a kernel-level execution model built on Linux task groups. Building on these principles, the paper presents the Task Group Bandwidth Server (TGBS), a kernel mechanism that enforces per-container CPU reservations using deadline-server abstractions and full virtual runqueues. Unlike the Hierarchical Constant Bandwidth Server (HCBS), which is limited to real-time (RT) workloads, TGBS applies uniformly to fair-share (FAIR), RT, and deadline-based (DL) scheduling classes. The experimental evaluation assesses functional behavior, real-time latency, and the execution of workloads sized analytically. Functional tests confirm correct enforcement of hierarchical reservations and priority ordering across scheduling classes. Latency measurements show that the overhead introduced by virtual runqueues remains moderate and comparable to HCBS. Finally, schedulability experiments demonstrate that reservations dimensioned with CSF are respected for real-time tasks in a mixed-policy environment, while highlighting the need for extended analytical models to fully capture FAIR scheduling. Overall, the results indicate that hierarchical reservations provide a practical path toward predictable and isolated execution of mixed-policy workloads on Linux. The work establishes a foundation that links analytical reservation sizing with kernel mechanisms and identifies future directions, including multicore support and improved multi-policy schedulability analysis.