Allocation-Internal Co-Scheduling - Interaction and Orchestration of Multiple Concurrent MPI Sessions

Heading towards exascale, the challenges for process management with respect to flexibility and efficiency grow accordingly. Running more than one application simultaneously on a node can be the solution for better resource utilization. However, this approach of co-scheduling can also be the way to go for gaining a degree of flexibility with respect to process management that can enable some kind of interactivity even in the domain of high-performance computing. This chapter gives an introduction into such co-scheduling policies for running multiple MPI sessions concurrently and interactively within a single user allocation. The chapter initially introduces a taxonomy for classifying the different characteristics of such a flexible process management, and discusses actual manifestations thereof during the course of the reading. In doing so, real world examples are motivated and presented by means of ParaStation MPI, a high-performance MPI library supplemented by a complete framework comprising a scalable and dynamic process manager. In particular, four scheduling policies, implemented in ParaStation MPI, are detailed and evaluated by applying a benchmarking tool that has especially been developed for measuring interactivity and dynamicity metrics of job schedulers and process managers for high-performance computing