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An Automatic MPI Process Mapping Method Considering Locality and Memory Congestion on NUMA Systems

MPI process mapping is an important step to achieve scalable performance on non-uniform memory access (NUMA) systems. Conventional approaches have focused only on improving the locality of communication. However, related studies have shown that on modern NUMA systems, the memory congestion problem could cause more severe performance degradation than the locality problem because a high number of processor cores in the systems can cause heavy congestion on shared caches and memory controllers. To optimize the process mapping, it is necessary to determine the communication behavior of the MPI processes. Previous methods rely on offline profiling to analyze the communication behavior, which incurs a high overhead and is potentially time-consuming. In this paper, we propose a method that automatically performs MPI process mapping for adapting to communication behaviors while considering both locality and memory congestion. Our method works at runtime during the execution of an MPI application. It does not require modifications to the application, previous knowledge of the communication behavior, or changes to the hardware and operating system. The proposed method has been evaluated with the NAS parallel benchmarks on a NUMA system. Experimental results show that our method can achieve performance close to an oracle-based mapping method with low overhead to the application execution. The performance improvement is up to 27.4% (13.4% on average) compared with the default mapping of the MPI runtime system.