Experiences with a Lightweight Supercomputer Kernel: Lessons Learned from Blue Gene's CNK

The Petascale era has recently been ushered in and many researchers have already turned their attention to the challenges of exascale computing. To achieve petascale computing two broad approaches for kernels were taken, a lightweight approach embodied by IBM Blue Gene's CNK, and a more fullweight approach embodied by Cray's CNL. There are strengths and weaknesses to each approach. Examining the current generation can provide insight as to what mechanisms may be needed for the exascale generation. The contributions of this paper are the experiences we had with CNK on Blue Gene/P. We demonstrate it is possible to implement a small lightweight kernel that scales well but still provides a Linux environment and functionality desired by HPC programmers. Such an approach provides the values of reproducibility, low noise, high and stable performance, reliability, and ease of effectively exploiting unique hardware features. We describe the strengths and weaknesses of this approach.