Making Effective Decisions in Computer Architects Real-World: Lessons and Experiences with Godson-2 Processor Designs

Although the design of many kinds of microprocessors has been underdeveloping for several decades, the computer architecture R\&D communitylacks well documented lessons and experiences about design decisions inthe research literature. In this paper, we systematically present thedesign decisions we made during the designing and prototyping of Godson-2series processors. The 250MHz Godson-2B, 450MHz Godson-2C, and 1GHzGodson-2E processors that implement 64-bit, four-issue, out-of-orderarchitecture were taped out in 2003, 2004, and 2005, respectively. Eachprocessor triples its predecessor in the SPEC CPU2000 rates. Ourfirst-hand experiences and lessons gained from these designs wouldprovide unique perspectives and insights that are not available in anyexisting text books and/or published papers. We summarize 10 criticallessons and experiences based on hundreds of our attempts atarchitectural and design optimizations for performance improvement ofGodson-2 series processors. The issues include silicon-simulationcorrelation, design balancing, performance optimizing, andpico-architecture tuning. We conclude that persistent improvement,attitude towards work-on-silicon design, and insightful understandingof software and fabrication process are the three most importantfactors for designing a high performance processor with low energyconsumption.