A Dynamic Network-Native MPI Partitioned Aggregation Over InfiniBand Verbs

Modern HPC systems require efficient hybrid programming model to utilize their hardware resources effectively. The Message Passing Interface (MPI) has accommodated next-generation hardware by providing new APIs such as the MPI Partitioned interface. This API provides a user with fine-grain communication without the overhead of traditional MPI point-to-point communication in multi-threaded workloads. To the best of our knowledge, we present the first work on detailed low-level design for an MPI Partitioned implementation. We guide readers through a method to map the MPI Partitioned interface to the InfiniBand Verbs API. Alongside implementation details, we also study the aggregation of user partitions and how we can efficiently send them over the network. We study a brute force approach and using the Partitioned LogGP (PLogGP) model to predict ideal aggregation. We observe that using the PLogGP model provides comparable performance without exhausting computing resources to search the entire solution space. The PLogGP design was further optimized by considering how the partition arrival pattern can be used to dynamically modify our aggregation scheme. We profiled our micro-benchmarks to provide analysis on how and why this additional optimization is beneficial to our results and how we can fine-tune this mechanism. Finally, we evaluated our PLogGP and Timer-based PLogGP designs with a commonly used communication pattern in HPC (communication sweep) to observe the impact when communicating with multiple processes in an application-like scenario at 1024 cores.