Unstructured adaptive meshes: bad for your memory?

The most important performance bottleneck in modern high-end computers is access to memory. Many forms of hardware and software support for reducing memory latency exist, but certain important applications defy these. Examples of such applications are unstructured adaptive (UA) mesh problems, which feature irregular, dynamically changing memory access. We describe a new benchmark program, called UA, for measuring the performance of computer systems when solving such problems. It complements the existing NAS Parallel Benchmarks suite that deals mainly with static, regular-stride memory references. The UA benchmark involves the solution of a stylized heat transfer problem in a cubic domain, discretized on an adaptively refined, unstructured mesh. We describe the numerical and implementation issues, and also present some interesting performance results.