Dynamic SimpleScalar: Simulating Java Virtual Machines

Current user-mode machine simulators typically do not support simulation of dynamic compilation, threads, or garbage collection, all of which Java Virtual Machines (JVMs) require. In this paper, we describe, evaluate, and validate Dynamic SimpleScalar (DSS). DSS is a tool that simulates Java programs running on a JVM, using just-in-time compilation, executing on a simulated multi-way issue, out-of-order execution superscalar processor with a sophisticated memory system. We describe the implementation of the minimal support necessary for simulating a JVM in SimpleScalar, including signals, thread scheduling, synchronization, and dynamic code generation, all required by a JVM. We validate our simulator using IBM Research’s Jikes RVM, a state-of-the-art JVM that runs Submitting to the First Annual IEEE/ACM International Symposium On Code Generation and Optimization. This work is supported by NSF ITR grant CCR-0085792, and DARPA grants F30602-98-1-0101 and F33615-01-C-1892, and International Business Machines Corporation. on a PowerPC architecture, and show that DSS loyally reflects the performance trends of a real JVM system. We then present a set of results using DSS. On the SPECjvm98 benchmarks, we study the best heap size for three different copying garbage collectors, and measure total, mutator, and collector memory characteristics. We compare our results with previous work, pointing out new insights, differences, and similarities. For example, we show there is a trade off between the locality benefits of copying collectors and the time to collect.