Non-Blocking PMI Extensions for Fast MPI Startup

An efficient implementation of the Process Management Interface (PMI) is crucial to enable fast start-up of MPI jobs. We propose three extensions to the PMI specification: 1) a blocking all gather collective (PMIX_Allgather), 2) a non-blocking all gather collective (PMIX_Iallgather), and 3) a non-blocking fence (PMIX_KVS_Ifence). We design and evaluate several PMI implementations to demonstrate how such extensions reduce MPI start-up cost. In particular, when sufficient work can be overlapped, these extensions allow for a constant initialization cost of MPI jobs at different core counts. At 16,384 cores, the designs lead to a speedup of 2.88 times over the state-of-the-art start-up schemes.