Time synchronization on SP1 and SP2 parallel systems

We describe an experimental time utility for synchronizing the operating system clocks on the SP1 and SP2 parallel system nodes. It synchronizes the node clocks typically within 5 microseconds of each other utilizing the synchronous feature of the SP1 and SP2 interconnection network. This is 2 to 3 orders of magnitude better than what can be achieved by previous methods. Synchronized clocks are useful for parallel program performance measurement and tuning, parallel program tracing and debugging, and gang scheduling of parallel processes, to name a few. We also measure the performance of a widely used time synchronization utility using the SP1 and SP2 interconnection network.