October 2025: Focused on refining the MGSC branch predictor in GEM5 to boost accuracy, efficiency, and stability. Delivered two feature workstreams and one maintenance fix, with direct impact on prediction quality and memory footprint, enabling more reliable simulations and better performance projections. Key commits include MGSC corrections, refactoring, and stability fixes.

Month 2025-09 — GEM5 (OpenXiangShan/GEM5) with a focus on Branch Predictor (MGSC/BTB) tuning and CPU-O3 predictor weight table enhancements. Delivered a set of coordinated predictor improvements and refactors that improve accuracy, stability, and modeling usefulness for architectural exploration.

August 2025 – OpenXiangShan/GEM5: Delivered major enhancements to branch predictor and strengthened simulator robustness, with targeted improvements for Xiangshan workloads. Key features include comprehensive branch predictor improvements (hashed path history for BTB, refined path history handling for unconditional branches, Xiangshan parameter tuning, PHR hashing refactor, MGSC indexing simplification) and extensive robustness fixes (prevention of undefined behavior in bit shifts/arithmetic and folding-related segmentation faults). These workstreams improved simulation fidelity, reliability, and maintainability. Impact: more accurate early-stage performance estimates, reduced debugging time, and cleaner, more maintainable GEM5 code. Technologies/skills demonstrated: C++, GEM5 internals, architectural modeling, PHR hashing, MGSC indexing, code refactoring, and defensive programming.

June 2025 monthly summary for OpenXiangShan/GEM5: Delivered a targeted performance optimization in the branch predictor's folded history path by replacing boost::dynamic_bitset with uint64_t. This reduced allocation overhead and improved runtime performance of the simulator. Refactored signatures and internal logic to operate on primitive integer types for faster bitwise operations and easier maintenance. All changes linked to commit 32688ae17341f3dfda33e18ed72f92a10c0cded4 (cpu: avoid using bitset in foldedhist (#418)). These improvements contribute to faster design-space exploration and more scalable GEM5 simulations.

May 2025 highlights for OpenXiangShan/GEM5: Strengthened build reliability and security with Nix upgrades, resolved Dramsim3 compilation in modern toolchains, and delivered GEM5 CPU model improvements for performance, accuracy, and portability. These changes reduce deployment risk, accelerate development cycles, and improve simulation fidelity.

2025-03 Monthly Summary for OpenXiangShan/GEM5 focusing on delivering business value through compatibility stabilization with modern toolchains and stabilizing developer workflows. Highlights include a critical patch set for toolchain compatibility and substantial tooling/build environment improvements to streamline development and onboarding.

January 2025 monthly summary focused on delivering performance, stability, and build hygiene across three OpenXiangShan repositories. Highlights include MMU and frontend timing optimizations, build system cleanup, and enhanced simulation fidelity to support faster development cycles and higher confidence in performance metrics.

December 2024: Two high-impact changes across OpenXiangShan/NEMU and OpenXiangShan/XiangShan focused on performance, reliability, and maintainability. In NEMU, default-off cross-page logging was implemented in the memory VA translation module to reduce log noise and potential performance impact. In XiangShan, the ITTAGE component was refactored with type annotations, removal of unused code, and function renaming to improve maintainability and IDE compatibility. These changes lower runtime overhead, enhance debug clarity, and set a solid foundation for safer future refactors across memory subsystems and instruction translation paths.

This month focused on delivering a key configurability enhancement for the First-In, First-Out Buffer (FTB) in OpenXiangShan/XiangShan. A new parameter was added to configure the FTB tag length, with updates to parameter definitions and the internal FTB logic to utilize the new setting. No major bugs were reported or fixed this month; the work emphasized feature delivery, code quality, and maintainability.

Monthly summary for 2024-10 focusing on business value and technical execution across the XiangShan frontend/CI improvements and bug fixes. Highlights include delivering frontend code quality improvements, enhancing CI format checks, and fixing a critical Frontend Buffer initialization bug to improve reliability.