Specialization and accelerators are being proposed as an effective way to address the slowdown of Dennard scaling. DySER is one such accelerator, which dynamically synthesizes large compound functional units to match program regions, using a co-designed compiler and microarchitecture. We have completed a full prototype implementation of DySER integrated into the OpenSPARC processor (called SPARC-DySER), a co-designed compiler in LLVM, and a detailed performance evaluation on an FPGA system, which runs an Ubuntu Linux distribution and full applications. Through the prototype, this paper evaluates the fundamental principles of DySER acceleration. Our two key findings are: i) the DySER execution model and microarchitecture provides energy efficient speedups and the integration of DySER does not introduce overheads – overall, DySER’s performance improvement to OpenSPARC is 6X, consuming only 200mW ; ii) on the compiler side, the DySER compiler is effective at extracting computationally intensive regular and irregular code. For non-computationally intense irregular code, two control flow shapes curtail the compiler’s effectiveness, and we identify potential adaptive mechanisms. Finally, our experience of bringing up an end-to-end prototype of an ISA-exposed accelerator has made clear that two particular artifacts are greatly needed to perform this type of design more quickly and effectively: 1) Open-source implementations of high-performance baseline processors, and 2) Declarative tools for quickly specifying combinations of known compiler transforms.

Accelerators and specialization in various forms are emerging as a way to increase processor performance. Examples include Navigo, Conservation-Cores, BERET, and DySER. While each of these employ different primitives and principles to achieve specialization, they share some common concerns with regards to implementation. Two of these concerns are: how to integrate them with a commercial processor and how to develop their compiler toolchain. This paper undertakes an implementation study of one design point: integration of DySER into OpenSPARC, a design we call OpenSPlySER. We report on our implementation exercise and quantitative results, and conclude with a set of our lessons learned. We demonstrate that DySER delivers on its goal of providing a non-intrusive accelerator design. OpenSPlySERruns on an Virtex-5 FPGA, boots unmodified Linux, and runs most of the SPECINT benchmarks with our compiler. Due to physical design constraints, speedups on full benchmarks are modest for the FPGA prototype. On targeted microbenchmarks, OpenSPlySER delivers up to a 31-fold speedup over the baseline OpenSPARC. We conclude with some lessons learned from this somewhat unique exercise of significantly modifying a commercial processor. To the best of our knowledge, this work is one of the most ambitious extensions of OpenSPARC.