We have modified Mach 3.0 to treat cross-domain remote procedure call (RPC) as a single entity, instead of a sequence of message passing operations. With RPC thus elevated, we improved the transfer of control during RPC by changing the thread model. Like most operating systems, Mach views threads as statically associated with a single task, with two threads involved in an RPC. An alternate model is that of migrating threads, in which, during RPC, a single thread abstraction moves between tasks with the logical flow of control, and "server" code is passively executed. We have compatibly replaced Mach's static threads with migrating threads, in an attempt to isolate this aspect of operating system design and implementation. The key element of our design is a decoupling of the thread abstraction into the execution context and the schedulable thread of control, consisting of a chain of contexts. A key element of our implementation is that threads are now "based" in the kernel, and temporar...

Traditional processor scheduling mechanisms in operating systems are fairly rigid, often supportingonly one fixed scheduling policy, or, at most, a few "scheduling classes" whose implementations are closely tied together in the OS kernel. This paper presents CPU inheritance scheduling, a novel processor scheduling framework in which arbitrary threads can act as schedulers for other threads. Widely different scheduling policies can be implemented under the framework, and many different policies can coexist in a single system, providing much greater scheduling flexibility. Modular, hierarchical control can be provided over the processor utilization of arbitrary administrative domains, such as processes, jobs, users, and groups, and the CPU resources consumed can be accounted for and attributed accurately. Applications, as well as the OS, can implement customized local scheduling policies; the framework ensures that all the different policies work together logically and predictably. As a ...

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The verification of timing properties is an important task in the validation process of embedded and real time systems. Temporal logic model checking is one of the most successful techniques as it allows the complete automation of the verification. In this paper, we present a new approach to symbolic QCTL (Quantitative CTL) model checking. In contrast to previous approaches we use an intuitive QCTL semantics, provide an efficient model representation and the new algorithms require less iteration steps compared to translating the QCTL problem into CTL and using standard CTL model checking techniques. The new model checking algorithm is based on a MTBDD representation. Some experimental results show the efficiency of the new approach.

Traditional processor scheduling mechanisms in operating systems are fairly rigid, often supporting only one fixed scheduling policy, or, at most, a few "scheduling classes" whose implementations are closely tied together in the OS kernel. This paper presents CPU inheritance scheduling,a novel processor scheduling framework in which arbitrary threads can act as schedulers for other threads. Widely different scheduling policies can be implemented under the framework, and many different policies can coexist in a single system, providing much greater scheduling flexibility. Modular, hierarchical control can be provided over the processor utilization of arbitrary administrative domains, such as processes, jobs, users, and groups, and the CPU resources consumed can be accounted for and attributed accurately. Applications as well as the OS can implement customized local scheduling policies; the framework ensures that all the different policies work together logically and predictably. As a side effect, the framework also cleanly addresses priority inversion by providinga generalized form of priority inheritance that automatically works within and among multiple diverse scheduling policies. CPU inheritance scheduling extends naturally to multiprocessors, and supports processor management techniques such as processor affinity [7] and scheduler activations [1]. Experimental results and simulations indicate that this framework can be provided with negligible overhead in typical situations, and fairly small (5-10%) performance degradation even in scheduling-intensive situations.

Large real-time software systems such as real-time Java virtual machines often use barrier protocols, which work for a dynamically varying number of threads without using centralized locking. Such barrier protocols, however, still suffer from priority inversion similar to centralized locking. We introduce gang priority management as a generic solution for avoiding unbounded priority inversion in barrier protocols. Our approach is either kernel-assisted (for efficiency) or library-based (for portability) but involves cooperation from the protocol designer (for generality). We implemented gang priority management in the Linux kernel and rewrote the garbage collection safe-point barrier protocol in IBM’s WebSphere Real Time Java Virtual Machine to exploit it. We run experiments on an 8-way SMP machine in a multi-user and multi-process environment, and show that by avoiding unbounded priority inversion, the maximum latency to reach a barrier point is reduced by a factor of 5.3 and the application jitter is reduced by a factor of 1.5. 1.