Improving compiler and run-time support for adaptive irregular codes

Irregular reductions form the core of adaptive irregular codes. On distributed-memory multiprocessors, they are parallelized either using sophisticated run-time systems (e.g., CHAOS, PILAR) or the shared-memory interface supported by software DSMs (e.g., CVM TreadMarks). We introduce LOCALWRITE, a new technique based on the owner-computes rule which eliminates the need for buffers or synchronized writes but may replicate computation. We evaluate its performance for irregular codes while varying connectivity locality, and adaptivity. LOCALWRITE improves performance by 50-150% compared to using replicated buffers, and can match or exceed gather/scatter for applications with low locality or high adaptivity.