Introspection of a Java™ virtual machine under simulation
Introspection of a Java™ virtual machine under simulation
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Java-based middleware is a rapidly growing workload for high-end server processors, particularly Chip Multiprocessors (CMP). To help architects design future microprocessors to run this important new workload, we provide a detailed characterization of two popular Java server benchmarks, ECperf and SPECjbb2000. We first estimate the amount of instruction-level parallelism in these workloads by simulating a very wide issue processor with perfect caches and perfect branch predictors. We then identify performance bottlenecks for these workloads on a more realistic processor by selectively idealizing individual processor structures. Finally, we combine our findings on available ILP in Java middleware with results from previous papers that characterize the availibility of TLP to investigate the optimal balance between ILP and TLP in CMPs. We find that, like other commercial workloads, Java middleware has only a small amount of instruction-level parallelism, even when run on very aggressive processors. When run on processors resembling currently available processors, the performance of Java middleware is limited by frequent traps, address translation and stalls in the memory system. We find that SPECjbb2000 differs from ECperf in two meaningful ways: (1) the performance of ECperf is affected much more by cache and TLB misses during instruction fetch and (2) SPECjbb2000 has more memory-level parallelism.