The gem5 Simulator: Version 20.0+

Abstract

This paper introduces the gem5 Simulator: Version 20.0+, detailing the evolution of this popular open-source computer architecture research tool over the last nine years. The simulator provides high-fidelity, cycle-level modeling capable of booting full operating systems and applications across major instruction sets including x86, Arm, and RISC-V. A key innovation highlighted is the transition to a formal governance model, designed to ensure continued community support and project relevance for future computer architecture research.

Report

Key Highlights

• Major Release: The paper documents the status and major changes associated with the gem5 Simulator Version 20.0+ release.
• Sustained Development: Over the nine years since the initial release, the project has accumulated over 7,500 commits from more than 250 unique contributors, reflecting robust community engagement.
• Formal Governance: The project has adopted a formal governance model to structure development and support, aiming for long-term project longevity (projected for the next 20 years).
• Core Research Tool: gem5 remains one of the most popular open-source infrastructures for cycle-level computer architecture modeling.

Technical Details

• Tool Functionality: gem5 operates as a simulation infrastructure providing cycle-level accuracy for modeling modern computer hardware.
• System Fidelity: The simulator achieves sufficient fidelity to boot unmodified Linux-based operating systems and execute full production applications.
• Supported Architectures (ISAs): The simulator maintains support for multiple critical instruction set architectures, specifically citing x86, Arm, and RISC-V.
• Codebase Health: Focus has been placed on improving code quality, fixing bugs, and adding new features throughout its development history.

Implications

• RISC-V Ecosystem Support: As one of the critical simulation tools, gem5's continued support and maturity are vital for the RISC-V ecosystem. Researchers and designers rely on gem5 to simulate new extensions, cores, and complex system-on-chip (SoC) interactions before tape-out.
• Architectural Research: The high fidelity and ability to run full application workloads across multiple competitive ISAs (x86, Arm, RISC-V) allows the academic community to conduct fair, detailed comparative studies on novel architectural ideas.
• Project Stability and Longevity: The adoption of a formal governance model is a crucial development. This assures researchers, industry partners, and community contributors that the gem5 platform will remain stable, actively maintained, and governed transparently, encouraging further investment in time and resources into the tool.
• Democratization of Architecture: By remaining open-source and highly detailed, gem5 lowers the barrier to entry for complex architecture exploration, benefiting both established institutions and emerging research groups globally.