Measuring VAX 8800 performance with a histogram hardware monitor

  • Authors:

  • D. W. Clark;P. J. Bannon;J. B. Keller

  • Affiliations:

  • Digital Equipment Corp., Littleton, MA;Digital Equipment Corp., Littleton, MA;Digital Equipment Corp., Littleton, MA

  • Venue:
  • ISCA '88 Proceedings of the 15th Annual International Symposium on Computer architecture
  • Year:
  • 1988

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Abstract

This paper reports the results of a study of VAX 8800 processor performance using a hardware monitor that collects histograms of the processor's micro-PC and memory bus status. 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 this paper's 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. The paper reports opcode and operand specifier frequencies, 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 very detailed picture of the amount of time an average VAX instruction spends in various activities on the 8800.