Clusters of workstations are being extensively used for solving computationally intensive scientific problems. However, there is limited support for quality of service (QoS) based distributed computing on commercial off- the-shelf (COTS) clusters. This limitation has restricted successful deployment of distributed real-time high-performance computing applications to customized and dedicated embedded multi-processor systems. This paper describes research work that attempts to provide a cluster platform that can guarantee access to computational and communication resources to distributed applications. The authors have developed PromisQoS, an architecture that supports execution of hard real-time distributed applications on a Linux cluster while providing high-throughput and low-latency communication using Myrinet. PromisQoS consists of the following major components - Hare, BDM-RT and Turtle. Hare is a prototype implementation of time-based QoS channels specified by the real-time message passing interface (MPI/RT 1.1) standard. BDM-RT is a low-level messaging library on Myrinet that provides deterministic communication latency and bandwidth on Myrinet. Turtle, a variant of RT-Linux, is the real-time operating system that provides guaranteed computation time. This work demonstrates that it is possible to deploy hard real-time distributed applications on COTS clusters and underlines the significance of the MPI/RT API in the realm of distributed high-performance computing applications that require QoS.

Clock synchronization is a fundamental requirement for any real-time distributed system operating with global schedules. The presence of a global clock permits co-scheduling, enhances the degree of synchronization between cooperating tasks of parallel programs, and permits implementation of quality of service (QoS) based communication. This paper describes the design and implementation of a high accuracy (/spl plusmn/5/spl mu/s) global clock on a Myrinet network of PC with low software overhead. The clock synchronization scheme uses a novel approach to reduce errors arising from variation of latency of transmitted clock values. The contribution of this work is that high-accuracy of clock synchronization is obtained without significant resource consumption. This makes the synchronization scheme equally suitable for high-performance and real-time distributed systems. The new approach achieves clock accuracy of the order of /spl plusmn/5/spl mu/s, compared to the other known clock synchronization algorithm on Myrinet that achieves accuracy of the order of milliseconds. Programmability of the Myrinet interface card and the presence of an on-board real time clock are critical to achieving this accuracy.

This paper describes the design and implementation of a real-time cluster of PCs that provides globally synchronized scheduling and predictable messaging passing. A high-accuracy, fine-grain global clock implementation has been closely coupled with a time-based scheduler to facilitate finely synchronized global scheduling across the cluster. A real-time messaging layer provides predictable communication latencies over the interconnecting Myrinet network. This system provides a solid framework for QoS based real-time communication, and in particular facilitates efficient layering of high-performance real-time distributed middleware such as MPI/RT. We present experiments and results to demonstrate the degree of predictability and synchronization achieved on an 8-node Myrinet cluster. 1 Introduction It is well known that clusters of commodity workstations are becoming a popular low cost alternative to super-computers for high-performance distributed computing [3]. Such systems also offe...

The Real-Time Message Passing Interface (MPI/RT) is a communication layer middleware standard that is aimed at providing guaranteed Quality of Service for data transfers on high performance networks. It poses "middleout" requirements both on applications and on the operating system. In this paper, we consider the "middledown" issues by modifying a POSIX compliant operating system in order to support hard real time scheduling, a feature needed for efficient MPI/RT on real-time Networks of Workstations (NOWs). This paper describes the evolution of Turtle, a variant of RT-Linux, that will later support a prototype implementation of time-driven MPI/RT. Analysis, design approach and results for Turtle are discussed.