Measuring VAX 8800 performance with a histogram hardware monitor

The results of a study of the VAX 8800 processor performance using a hardware monitor that collects histograms of the processor´s micro-PC and memory bus status are presented. The monitor keeps a count of all machine cycles executed at each micro-PC location, as well as counting all occurrences of each bus transaction. It can measure a running system without interfering with it, and these results are based on measurements of live timesharing. Because the 8800 is a microcoded machine, a great deal of information can be gleaned from these data. Opcode and operand specifier frequencies are reported, as well as the amount of time spent in instruction execution and various kinds of overhead, such as memory management and cache-wait stalls. The histogram method yields a detailed picture of the amount of time an average VAX instruction spends in various activities on the 8800