On the Design and Evaluation of a Real-Time Operating System for Cache-Coherent Multicore Architectures

Abstract

The uncontrolled use of the cache hierarchy in a multicore processor by real-time tasks may impact their worst-case execution times. Several operating system techniques have been recently proposed to deal with caches in a multiprocessor in order to improve predictability, such as cache partitioning, cache locking, and real-time scheduling. However, the contention caused by the cache coherence protocol and its implication for real-time tasks is still an open problem. In this paper, we present the design and evaluation of a real-time operating system for cache-coherent multicore architectures. The real-time operating system infrastructure includes real-time schedulers, cache partitioning, and cache coherence contention detection through hardware performance counters. We evaluate the real-time operating system in terms of run-time overhead, schedulability of realtime tasks, cache partitioning performance, and hardware performance counters usability. Our results indicate that: (i) a real-time operating system designed from scratch reduces the run-time overhead, and thus improves the realtime schedulability, when compared to a patched operating system; (ii) cache partitioning reduces the contention in the shared cache and provides safe real-time bounds; and (iii) hardware performance counters can detect when real-time tasks interfere with each other at the shared cache level. Scheduling, cache partitioning, and hardware performance counters together are a step-forward to provide real-time bounds in cache-coherent architectures.