Periodic Phase Adjustment Distributed Clock Synchronization in the Hard Realtime Environment.

摘要

Many multiprocessing and distributed-processing system applications require the various components of the system to have access to the same knowledge of the current time of day. Uses for time-of-day data include the generation of timestamps for the coordination of transactions in a database system, the detection of process faults without the limitations of timeout in distributed fault-tolerant systems, and the recording and predicting of physical world events in a realtime system. There are various alternative methods of coordinating database transactions which avoid time-of-day timestamps, such as traditional locking mechanisms and timestamps employing virtual time. There is no alternative for time-of-day facilities in a system designed to act upon real-world, time-oriented events. This paper describes the operation and rationale underlying an approach to synchronizing a set of time-of-day realtime clocks located on the respective processors of a distributed processing system. The approach is called periodic phase adjustment. The paper also shows how to integrate this approach into rate monotonic hard-deadline realtime scheduling technology. (KR)