An occam Style Communications System for UNIX Networks

This document describes the design of a communications system which provides occam style communications primitives under a Unix environment, using TCP/IP protocols, and any number of other protocols deemed suitable as underlying transport layers. The system will integrate with a low overhead scheduler/kernel without incurring significant costs to the execution of processes within the run time environment. A survey of relevant occam and occam3 features and related research is followed by a look at the Unix and TCP/IP facilities which determine our working constraints, and a description of the T9000 transputer's Virtual Channel Processor, which was instrumental in our formulation. Drawing from the information presented here, a design for the communications system is subsequently proposed. Finally, a preliminary investigation of methods for lightweight access control to shared resources in an environment which does not provide support for critical sections, semaphores, or busy waiting, is made. This is presented with relevance to mutual exclusion problems which arise within the proposed design. Future directions for the evolution of this project are discussed in conclusion

Automatic code generation for ATLAS communications drivers

ATLAS is a software development platform created in our Department. Among other benefits, it provides support to easily distribute applications over a network. In these applications, communications issues among the different processes should be faced. Pursuing to isolate application developers from the intricacies of these issues, communication drivers are automatically generated from an interface declaration of each process. This automatic code generation --not unlike the generation of stubs in CORBA from the IDL specification-- is the main topic of this report.Postprint (published version

Automatic User Interaction Detection and Scheduling with RSIO

Response time is one of the most important factors for the overall usability of a computer system. We present RSIO, a processor scheduling framework for improving the response time of latency-sensitive applications by monitoring accesses to I/O channels and inferring when user interactions occur. RSIO provides a general mechanism for all user interactions, including direct interactions via local HCI devices such as mouse and keyboard, indirect interactions through middleware, and remote interactions through networks. It automatically and dynamically identifies processes involved in a user interaction and boosts their priorities at the time the interaction occurs to improve system response time. RSIO detects processes that directly handle a user interaction as well as those indirectly involved in processing the interaction, automatically accounting for dependencies and boosting their priorities accordingly. RSIO works with existing schedulers, processes that may mix interactive and batch activities, and requires no application modifications to identify periods of latency-sensitive application activity. We have implemented RSIO in Linux and measured its effectiveness on microbenchmarks and real applications. Our results show that RSIO is easy to use and can provide substantial improvements in system performance for latency-sensitive applications

MINIX4RT: real-time interprocess communications facilities

MINIX4RT es una extensión del conocido Sistema Operativo MINIX que incorpora servicios de Tiempo Real Estricto en un nuevo microkernel pero manteniendo compatibilidad con las versiones anteriores del MINIX estándar. La Comunicación entre Procesos es un mecanismo que permite hacer extensible a un Sistema Operativo, pero debe estar libre de Inversión de Prioridades para ser utilizado en aplicaciones de Tiempo Real. Como las primitivas de MINIX no disponen de esta funcionalidad, se incorporaron nuevas primitivas de Comunicación entre Procesos al microkernel de Tiempo Real. El presente artículo describe las facilidades de Comunicaciones entre Procesos en Tiempo Real disponibles en MINIX4RT, su diseño, implementación, tests de desempeño y sus resultados.MINIX4RT is an extension of the well-known MINIX Operating System that adds Hard Real-Time services in a new microkernel but keeping backward compatibility with standard MINIX versions. Interprocess Communications provides a mechanism to make Operating System extensible, but they must be Priority Inversion free for Real-Time applications. As MINIX Interprocess Communications primitives does not have this functionality, new primitives were added to the Real-Time microkernel. This article describes the Real- Time Interprocess Communications facilities available on MINIX4RT, its design, implementation, performance tests and their results.I Workshop de Arquitecturas, Redes y Sistemas Operativos (WARSO)Red de Universidades con Carreras en Informática (RedUNCI

RK: A Real-Time Kernel for a Distributed System With Predictable Response

Robotics applications must execute in real-time. In addition, complex robotics applications include many physically distributed components such as manipulator arms and sensors. This paper presents the real-time kernel RK which is designed to facilitate the development of a distributed sensory system with multiple arms and sensors. The goal of the kernel is to support distributed applications that require predictable timing behavior. Our kernel design guarantees predictable response times by scheduling processes and communications based on timing constraints. In addition, the kernel provides a set of primitives that can be used to implement applications requiring predictable timing behavior. These primitives allow the specification of timing requirements that can be guaranteed in advance by the scheduler and the direct control of devices by application processes for faster and predictable feedback control. To illustrate the use of our kernel, this paper also describes a multiple sensory system which is being ported to our distributed test-bed

Automatic User Interaction Detection and Scheduling with RSIO

Response time is one of the most important factors for the overall usability of a computer system. We present RSIO, a processor scheduling framework for improving the response time of latency-sensitive applications by monitoring accesses to I/O channels and inferring when user interactions occur. RSIO provides a general mechanism for all user interactions, including direct interactions via local HCI devices such as mouse and keyboard, indirect interactions through middleware, and remote interactions through networks. It automatically and dynamically identifies processes involved in a user interaction and boosts their priorities at the time the interaction occurs to improve system response time. RSIO detects processes that directly handle a user interaction as well as those indirectly involved in processing the interaction, automatically accounting for dependencies and boosting their priorities accordingly. RSIO works with existing schedulers, processes that may mix interactive and batch activities, and requires no application modifications to identify periods of latency-sensitive application activity. We have implemented RSIO in Linux and measured its effectiveness on microbenchmarks and real applications. Our results show that RSIO is easy to use and can provide substantial improvements in system performance for latency-sensitive applications

Computing infrastructure issues in distributed communications systems : a survey of operating system transport system architectures

The performance of distributed applications (such as file transfer, remote login, tele-conferencing, full-motion video, and scientific visualization) is influenced by several factors that interact in complex ways. In particular, application performance is significantly affected both by communication infrastructure factors and computing infrastructure factors. Several communication infrastructure factors include channel speed, bit-error rate, and congestion at intermediate switching nodes. Computing infrastructure factors include (among other things) both protocol processing activities (such as connection management, flow control, error detection, and retransmission) and general operating system factors (such as memory latency, CPU speed, interrupt and context switching overhead, process architecture, and message buffering). Due to a several orders of magnitude increase in network channel speed and an increase in application diversity, performance bottlenecks are shifting from the network factors to the transport system factors.This paper defines an abstraction called an "Operating System Transport System Architecture" (OSTSA) that is used to classify the major components and services in the computing infrastructure. End-to-end network protocols such as TCP, TP4, VMTP, XTP, and Delta-t typically run on general-purpose computers, where they utilize various operating system resources such as processors, virtual memory, and network controllers. The OSTSA provides services that integrate these resources to support distributed applications running on local and wide area networks.A taxonomy is presented to evaluate OSTSAs in terms of their support for protocol processing activities. We use this taxonomy to compare and contrast five general-purpose commercial and experimental operating systems including System V UNIX, BSD UNIX, the x-kernel, Choices, and Xinu

Study of fault-tolerant software technology

Presented is an overview of the current state of the art of fault-tolerant software and an analysis of quantitative techniques and models developed to assess its impact. It examines research efforts as well as experience gained from commercial application of these techniques. The paper also addresses the computer architecture and design implications on hardware, operating systems and programming languages (including Ada) of using fault-tolerant software in real-time aerospace applications. It concludes that fault-tolerant software has progressed beyond the pure research state. The paper also finds that, although not perfectly matched, newer architectural and language capabilities provide many of the notations and functions needed to effectively and efficiently implement software fault-tolerance