OpenXiangShan/GEM5 (2025-10) monthly summary: delivered stability and performance improvements for branch target buffers (MBTB/UBTB). Implemented in-place updates for the victim cache, refined branch prediction update logic, simplified MicroTAGE parameter settings, and removed duplicate victim cache entries to enhance correctness and performance. This work, anchored by commit 5aff2c49d7427668c82b4baff1f9567254a76e43 ("Fix mbtb vc perf (#575)"), reduces stale state and improves prediction accuracy, contributing to faster and more reliable simulations and better guidance for hardware design decisions.

September 2025 monthly summary for OpenXiangShan/GEM5: Key predictor enhancements, testing/CI improvements, and a bug fix; improved observability and configurability enabling faster performance tuning and more robust validation.

August 2025 — OpenXiangShan/GEM5 monthly summary: Architectural refinements, expanded verification, and fidelity improvements backed by stronger CI/CD workflows and deeper performance modeling. Delivered MBTB/BTB refactor with a dual SRAM design and victim cache, comprehensive BTBRAS unit tests with RAS docs, and GEM5 benchmarking improvements (2048-set TAGE, SE alignment) plus a robust microbenchmark suite. CI/CD resilience enhancements and CPU performance modeling refinements provide reliable validation, reproducible results, and clearer performance signals for real workloads.

July 2025 monthly summary for OpenXiangShan/GEM5: Delivered major refactors to the O3 fetch/status subsystem, optimized TAGE branch predictor configuration, and fixed a critical bug in the dual cacheline fetch path. These changes improved correctness and reliability of the instruction fetch path, reduced area in the predictor, and eliminated a source of retry-related duplicates, contributing to better performance, robustness, and maintainability across the project.

June 2025 performance-focused delivery for OpenXiangShan/GEM5. Executed a comprehensive fetch-pipeline overhaul for O3 CPU, including FTQ integration, fetch buffer encapsulation, and robust translation/cache fetch flow enhancements to improve throughput and robustness. Implemented significant bug fixes in the fetch path (two explicit fixes addressing misaligned fetch handling and 2-byte alignment issues) and refined cache-request flow (unified sendNextCacheRequest and FTQ-granular inst fetch). Increased L1 I-cache MSHR, expanded fetch capabilities for dual-cacheline handling, and adjusted fetch buffer sizing (64→66) to support higher concurrency. Expanded observability and CI capabilities with cycle-accurate DPRINTF logging, improved cycle management, and automated performance data archiving in CI workflows. Documented external contributions and tidied CI configurations to reduce flakiness and improve project hygiene. These efforts deliver lower fetch latency, higher instruction throughput, improved debugability, and a stronger foundation for future performance optimizations.

May 2025 monthly summary: Implemented and stabilized the MGSC-based predictor in cpu-o3, with stage movement to s4 when tage is in s3, and completed key refactors to improve maintainability. Fixed critical runtime and history-handling bugs, optimized the prediction path, and enhanced fetch/refactor work. Delivered documentation updates and CI improvements to accelerate feedback and reduce resource usage, and performed cleanup of unused tooling.

April 2025 performance summary for OpenXiangShan/GEM5: substantial architectural refactor and predictor enhancements for BTB/TAGE and BPU, including integration of TimedBaseBTBPredictor and improvements to tick, squash, and history recovery. Strengthened quality assurance through a new unit-testing framework and extensive tests across the fetch and predictor pipelines. Implemented a dedicated unit test framework for DecoupledBPUWithBTB and updated tests (abtb, Jump Ahead Predictor, Fetch Target Queue). Refined the fetch stage with tracing and removal of loop buffer support. Enhanced BTB statistics tracking and corrected key bugs (abtb test regression after rebase; foldedHist maxShamt updated from 8 to 16). These changes deliver higher branch prediction accuracy, faster iteration cycles, better observability, and a scalable foundation for further performance tuning.

OpenXiangShan/GEM5 — March 2025: Strengthened the XiangShan GEM5 branch predictor stack with feature-rich BTB/TAGE enhancements, expanded test coverage, and CI improvements to improve accuracy, reliability, and performance evaluation cycles. Delivered decoupled BPU with BTB support, unified BTB parameters, non-block-aligned and half-aligned BTB variants, and refactor/clarifications across the BTB/TAGE code paths. Expanded validation with comprehensive unit tests and μRAS suites, plus documentation and localization efforts (Chinese README). Invested in tooling and CI to reduce validation time and improve build stability, enabling faster performance modeling for product planning and hardware exploration. Key features delivered include: DecoupledBPUWithBTB support; unified numDelay parameter for BTB predictors; parameterized BTB blockSize; support for non-block-aligned and half-aligned BTB; comprehensive BTB unit tests and μRAS tests; BTBTAGE lookup/prediction refactor; compilation database generation; Chinese README for XiangShan GEM5 branch predictor; GitHub Actions CI for ideal BTB performance; and related documentation enhancements. Major bugs fixed include: BTB compile bug with clang CC; CI coredump fix for BTB tests; BTB tag update bug fix after a match is found; unit test stability improvements (to_string removal in tage/ittage and associated fixes). Overall impact and accomplishments: Significantly improved branch prediction accuracy and reliability for the GEM5 model, with broader test coverage and automated validation, reducing time-to-performance insight. The changes enable more realistic architectural exploration, faster performance evaluation cycles, and better maintainability through refactoring and documentation. Technologies/skills demonstrated: C++/system C++ design; BTB/TAGE architecture and predictor engineering; modular code refactoring; comprehensive unit testing; CI automation (GitHub Actions); build tooling (clang compatibility); documentation and localization; performance-oriented validation.

February 2025 monthly summary for OpenXiangShan/GEM5 focusing on delivering reliable CI enhancements and environment parity improvements. Tech debt reduction achieved by introducing final abort checks in the CI pipeline, reporting abort counts, listing the first 10 failed tests, and exiting with a non-zero status on failures. Also updated CI jobs to run on open servers to ensure tests execute in the intended environment. This work demonstrates strong CI/CD engineering, test automation, and environment configuration skills, directly contributing to faster feedback cycles and more reliable builds.

January 2025 performance and architecture-focused delivery for OpenXiangShan/GEM5. This month prioritized memory subsystem tuning, reliable FP workloads, build-time performance optimizations, and CI/DRAMSim3 integration to accelerate development cycles and improve simulation throughput. Deliverables span enhancements to cache resources, PGO-based builds, FP/workload reliability, and instrumentation for deeper bottleneck diagnostics, with strong emphasis on business value through faster iterations and more actionable performance data.

December 2024 performance-focused monthly summary for OpenXiangShan/GEM5. The main deliverables focused on performance, configurability, and observability enhancements across the GEM5 platform, aligned with business value of faster iteration, better profiling, and optimized runtime performance.