Application-Specific Service Technologies for Commodity Operating Systems in Real-Time Environments
In order to eliminate the costs of proprietary systems and special purpose hardware, many real-time and embedded computing platforms are being built on commodity operating systems and generic hardware. Unfortunately, many such systems are ill-suited to the low-latency and predictable timing requirements of real-time applications. This article, therefore, focuses on application-specific service technologies for low-cost commodity operating systems and hardware, so that real-time service guarantees can be met. We describe contrasting methods to deploy first-class services on commodity systems that are dispatched with low latency and execute asynchronously according to bounds on CPU, memory, and I/O device usage. Specifically, we present a "user-level sandboxing" (ULS) mechanism that relies on hardware protection to isolate application-specific services from the core kernel. This approach is compared with a hybrid language and runtime protection scheme, called SafeX, that allows untrusted services to be dynamically linked and loaded into a base kernel. SafeX and ULS have been implemented on commodity Linux systems. Experimental results have shown-that both approaches are capable of reducing service violations (and, hence, better qualities of service) for real-time tasks, compared to traditional user-level methods of service deployment in process-private address spaces. ULS imposes minimal additional overheads on service dispatch latency compared to SafeX, with the advantage that it does not require application-specific services to execute in the trusted kernel domain. As evidence of the potential capabilities of ULS, we show how a user-level networking stack can be implemented to avoid data copying via the kernel and allow packet processing without explicit process scheduling. This improves throughput and reduces jitter.
predictability experimentation design system extensibility