online system performance measurements with software and hybrid monitors
Two monitors were implemented to collect information about the behavior of the online system developed and run at Stanford. The response of this online system was slow and main memory was a critical resource. The goal was to extract desired information by a method that requires only a negligible amount of monitored system resources. Results presented in this paper indicate that this effort has been successful. A software monitor that requires less than 700 bytes of main memory collects statistics about utilization of special online system resources and about the scheduler mechanism, detects system deadlocks, and measures online executive overhead. This software monitor helped to discover various facts about the system behavior; however, to understand the reasons behind certain situations, it was necessary to learn more about properties of individual terminal tasks. Since a software monitor would cause an intolerable system degradation and hardware monitoring is not directly applicable for such measurements, a hardware/software monitor interface was implemented which enables recording of software events by a hardware monitor. The monitoring artifact is thus kept close to zero. This technique has been applied to measure time a task spends in various states and it has many other uses.
online systems performance measurement measurement software hybrid monitor collect informal behavior response memorialized critic resource extraction method paper statistics scheduling deadlock reasoning situated learning terminals task hardware interfaces records event timing