Stramash: A Fused-kernel Operating System For Cache-Coherent, Heterogeneous-ISA Platforms

Abstract

We live in the world of heterogeneous computing. With specialised elements reaching all aspects of our computer systems and their prevalence only growing,we must act to rein in their inherent complexity. One area that has seen significantly less investment in terms of development is heterogeneous-ISA systems, specifically because of complexity. To date, heterogeneous- ISA processors have required significant software overheads,workarounds, and coordination layers, making the development ofmore advanced software hard, and motivating little further development of more advanced hardware.

In this paper, we take a fused approach to heterogeneity, and introduce a new operating system (OS) design, the fused-kernel OS, which goes beyond the multiple-kernel OS design, exploiting cache-coherent shared memory among heterogeneous-ISA CPUs as a first principle – introducing a set of newOS kernel mechanisms.We built a prototype fusedkernel OS, Stramash-Linux, to demonstrate the applicability of our design to monolithic OS kernels.We profile Stramash OS components on real hardware but tested them on an architectural simulator – Stramash-QEMU, which we design and build. Our evaluation begins by validating the accuracy of our simulator, achieving an average of less than4%errors.We then perform a direct comparison between our fused-kernelOSand state-of-the-art multiple-kernel OS designs. Results demonstrate speedups of up to 2.1×onNPBbenchmarks. Further,we provide an in-depth analysis of the differences and trade-offs between fused-kernel and multiple-kernel OS designs.