Performance Monitoring in a Time-Sharing System A software measurement facility which is part of a general purpose time-sharing system is described. The Date Collection Facility (DCF) has been implemented in the Michigan Terminal System (MTS) for the System/360 model 67. It exists for the purpose of monitoring operating system and user program behavior and performance. The overall structure of MTS is outlined in order to explain the implementation of the DCF. Events in the system are identified and recorded from within the supervisor, and dumped to magnetic tape by an auxiliary program for off-line processing. Events in user programs which are unrelated to system actions are recorded with a supervisor call. The time of occurrence of each event is accurately recorded, and data items are further identified by job and type. The overhead associated with data collection and its interference with normal jobs is carefully analyzed, and both are shown to be minimal. Several examples are given of information obtained with the facility and of applications in which it has been useful. Some general guidelines are offered for the construction of future monitoring programs. CACM November, 1969 Pinkerton, T. B. performance monitoring, performance measurement, program behavior, performance data, multiprogramming performance, software measurement, time-sharing performance, system evaluation, software monitor, software instrumentation 4.31 4.32 4.39 4.42 4.43 CA691103 JB February 15, 1978 1:07 PM 1827 5 1827 1827 5 1827 1827 5 1827 2667 5 1827 2668 5 1827 1604 6 1827 1604 6 1827 1728 6 1827 1728 6 1827 1761 6 1827 1827 6 1827 1827 6 1827 2677 6 1827