A Fine-Grain Clock Synchronization Mechanism for QoS Based Communication on Myrinet

Clock synchronization is a fundamental requirement for any real-time distributed system operating with global schedules. This paper describes the design and implementation of a high accuracy (±4 μs) global clock on a Myrinet [4] gigabit/s system area network of PCs with considerably low software overheads. The global clock is based on a master-slave internal clock synchronization scheme [15]. A novel approach has been adopted to improve synchronization accuracy. The programmability of the Myrinet interface card and the presence of an on-board Real Time Clock [4] have been utilized to counter the undesirable effects of unpredictability in the latency of clock messages. The resulting synchronization facilitates global scheduling of distributed real-time tasks, and provides a framework to build support for Quality of Service in distributed high-performance environments.