Exploring the Design Space of Combining Linux with Lightweight Kernels for Extreme Scale Computing

As systems sizes increase to exascale and beyond, there is a need to enhance the system software to meet the needs and challenges of applications. The evolutionary versus revolutionary debate can be set aside by providing system software that simultaneously supports existing and new programming models. The seemingly contradictory requirements of scalable performance and traditional rich programming APIs (POSIX, and Linux in particular) suggest that approach, and has lead to a new class of research. Traditionally, operating systems for extreme-scale computing have followed two approaches: they have either started with a full-weight kernel (FWK), typically Linux, and removed features which were impeding performance and scalability, or they started with a light-weight kernel (LWK), and added capability to provide Linux compatibility. Neither of these approaches, succeed in retaining full Linux compatibility and achieving high scalability. To overcome this problem, we have been exploring the design space of providing LWK performance while retaining the Linux APIs and Linux environment. Our hybrid solution is to run Linux and an LWK side-by-side on the same node. HPC applications execute on top of the LWK, but the system selectively provides OS features by leveraging the Linux kernel. In this paper, we discuss two possible methods of achieving the symbiosis between the two kernels and the trade-offs between them. Specifically, we detail and contrast two particular approaches, Intel's mOS project and IHK/McKernel, an effort lead by RIKEN Advanced Institute for Computational Science.