A Methodology for Improving gXR5 Speed and Accuracy

Abstract

Computer Architects often walk the tightrope between performance, power and area while designing modern day processors. This daunting task is made even more challenging by short Time-to-Market requirements set by the clients. In light of these challenges, architectural simulators provide a much needed tool for the architects to gauge the impact of their innovations rather quickly. Arguably, use of such simulators is essential in avoiding a product recall due to the processor failing to deliver on performance/power requirements for the intended application. The thesis is in-line with the objective of identifying and addressing the bottlenecks in the RISC-V simulation ecosystem and contribute in the development of RISC-V infrastructure.
The intended objective of an architectural simulator is to capture the trend of the real hardware (i.e., performance improvement due to micro-architectural changes in real hardware should be eloquently captured by the simulator). A good simulator shall have high throughput (less simulation time) and should be easily re-configurable. The re-configurability of the simulator can be as fine as micro-architectural changes or as large as a new ISA being simulated. These attributes of speed and re-configurability come at the cost of accuracy. A high error in performance statistics of the simulator fails to engender confidence among the prospective users. Hence, validating performance of simulators against hardware is essential.
The thesis introduces the need for a full system architectural simulator for RISC-V processors followed by a brief, yet crisp review of the past attempts at making such simulators. The review is from the perspective of existing methodologies for performance validation of the simulators. The work also proposes a new methodology for validating system simulators. Although, the proposed methodology is generic and can be extended to other ISAs (such as ARM, x86, etc.), the target hardware chosen are RISC-V ISA based systems that span both commercially, IP protected processor as well as open-source processors widely adopted by the RISC-V community.
The error in validated simulator is reduced to 22.9% and 18.9% for selected SPEC2017 benchmarks applications, by calibrating the CPU model. The methodology also streamlines CPU performance validation of the simulators.