Performance of the VAX-11/780 translation buffer

Abstract

A virtual-address translation buffer (TB) is a hardware cache of recently used virtual-to-physical address mappings. The authors present the results of a set of measurements and simulations of translation buffer performance in the VAX-11/780. Two different hardware monitors were attached to VAX-11/780 computers, and translation buffer behavior was measured. Measurements were made under normal time-sharing use and while running reproducible synthetic time-sharing work loads. Reported measurements include the miss ratios of data and instruction references, the rate of TB invalidations due to context switches, and the amount of time taken to service TB misses. Additional hardware measurements were made with half the TB disabled. Trace-driven simulations of several programs were also run; the traces captured system activity as well as user-mode execution. Several variants of the 11/780 TB structure were simulated.