Monitoring strategies for hypercube systems

The basis for analyzing and improving the reliability and efficiency of software is a monitoring tool. Besides the usual difficulties of diagnostic tools, parallel computing also introduces the probe effect to the monitoring process. This effect describes altered program behaviors observed when delays are introduced into concurrent programs through the use of instrumentation. The probability of the probe effect depends on the amount of overhead that is produced with the monitoring functionality. The paper describes the Event Monitoring Utility EMU, which offers an approach for monitoring of distributed memory multiprocessors. The current implementation takes advantage of the hypercube topology for further reduction of the overhead caused by the instrumentation. Therefore EMU contains various monitoring models with different impact on the observed program. The knowledge of these models can help the user to reduce the overhead of the monitor as much as possible.