Abstract—Since the advent of multi-core processors, the physionomy of typical clusters has dramatically evolved. This new massively multi-core era is a major change in architecture, causing the evolution of programming models towards hybrid MPI+threads, therefore requiring new features at low-level. Modern communication subsystems now have to deal with multithreading: the impact of thread-safety, the contention on network interfaces or the consequence of data locality on performance have to be studied carefully. In this paper, we present PIOMan, a scalable and generic lightweight task scheduling system for communication libraries. It is designed to ensure concurrent progression of multiple tasks of a communication library (polling, offload, multi-rail) through the use of multiple cores, while preserving locality to avoid contention and allow a scalability to a large number of cores and threads. We have implemented the model, evaluated its performance, and compared it to state of the...