Application-Specific Service Technologies for Commodity Operating Systems in Real-Time Environments

摘要

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.