Performance evaluation of a DySER FPGA prototype system spanning the compiler, microarchitecture, and hardware implementation

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.