January 2026: Delivered a Branch Target Buffer (BTB) refactor for Fetch Targeting in OpenXiangShan/GEM5. Replaced fetch streams with fetch targets to simplify the prediction path, improve clarity, and lay groundwork for performance improvements in the instruction fetch/prediction pipeline. This change reduces pipeline coupling and enhances maintainability, enabling faster future optimizations and more reliable branch prediction behavior.

December 2025 monthly summary for OpenXiangShan development, highlighting business value and technical achievements across Utility and GEM5. Key deliverables include memory tracing enhancements, CPU pipeline improvements, correctness serialization, and tooling improvements, resulting in improved diagnosability, scheduling throughput, memory reference efficiency, and performance analysis capabilities.

November 2025 (OpenXiangShan/GEM5) delivered notable improvements in scheduling efficiency, configurability, and observability while addressing critical correctness and performance issues in the OoO core and cache subsystem. Key features extended the FP data path and memory interactions, restructured configuration management, and expanded performance analysis capability with load lifetime tracking. Consequent bug fixes strengthened timing accuracy, replacement policy behavior, and replay handling, contributing to more reliable simulations and faster iteration cycles for hardware-software co-design. Key features delivered: - KMHV3Scheduler FP/FP wakeup channel enhancements: added new FP-to-mem and mem-to-FP wakeup channels to improve scheduling efficiency and dataflow between banks (commit be640a22cca5c65d4acc2efb4329e2951d3be351). - GEM5 configuration organization: reorganized simulator configs for clarity and maintainability (commit 1df4f1678a668c76f23fbf6d838df96e4c3c2d8e). - Integer/FP conversion support in CPU OoO and scheduler: added int2fp FU and kmhv2 intcvt FU enabling mixed-precision arithmetic (commits 1c2440df6d6b11e998f0907d49992cc71a892d60 and 06691bb94c7894573feecf79dfbbd60c76a74141). - Load lifetime tracking in performance monitoring: added a database table for load lifetime traces and extended instruction metadata with virtual/physical addresses, replay reasons, and timestamps (commit 80160083468dbd8124adc356650b0864f32879c0). Major bugs fixed: - L2Wrapper replacement policy and cache slice improvements: fix replacement policy issues and ensure proper slice size division and adaptation (commit 9955f5159b8fbdac7b3e8e6eb4fd7367ceb05fa8). - FP latency alignment for FCMP/FCVT: align latency values in CPU OoO unit to improve timing accuracy (commit a65b90b8b50afc513a1e571765e29627e048cfb3). - CPU OoO execution correctness improvements: fix warmup dump after warmup and correct RAW/RAR replay handling (commits 69b4913b0d1e45483f0b6b87b773bdce5ba22b21 and 67de9931e552d2a08949f8561e7a41dc6dd93be3). Overall impact: The month delivered tangible business value by enabling faster design-space exploration, more accurate performance modeling, and cleaner, more maintainable configurations, while reducing risk of timing and correctness bugs in OoO execution. These changes collectively shorten iteration cycles and improve confidence in GEM5-based simulations. Technologies/skills demonstrated: CPU OoO design, floating-point and integer conversion, cache architecture, wakeup path optimization, simulation configuration management, and performance instrumentation.

Month 2025-10 – OpenXiangShan/GEM5: Delivered notable O3 pipeline enhancements, stabilized simulation config, and fixed critical CSR timing/loading issues, materially contributing to performance potential and analysis fidelity. Key work included ISA/scheduler improvements with IntJpOp and a multi-bank register file, instruction fusion for loads and ALU+load sequences, and a CSR time/load fault fix with sim config updates (including replacing h-nemu). These changes increase execution efficiency, broaden ISA capabilities, and improve simulation accuracy for performance evaluation.

September 2025 Performance Review - OpenXiangShan projects Key focus this month was on enhancing FP accuracy and observability across the GEM5 CPU model and expanding tracing capabilities in Utility. The work delivered targeted optimizations to floating-point scheduling and latency modeling, plus a set of tracing improvements that enable deeper performance analysis with XSPdb support. Impact-oriented highlights include improved FP throughput modeling, reduced FP division cost, and richer trace export suitable for performance investigations and capacity planning.

OpenXiangShan/GEM5 – August 2025: Delivered targeted performance modeling improvements across O3/RISC-V and ARM-v2 paths, plus memory subsystem accuracy refinements. The changes enhance simulation fidelity, enable more precise performance analysis, and improve resource utilization in critical paths. Key outcomes include extended instruction fusion framework with new patterns, corrected fusion accounting in O3 stats, refined ARM-v2 scheduler/resource management, store buffer bank conflict checks, and FP division pipeline improvements, contributing to higher throughput and more reliable microarchitectural modeling.

July 2025: Delivered substantial OpenXiangShan GEM5 O3 CPU pipeline enhancements and targeted configuration changes to improve performance potential, configurability, and maintainability. Key work focused on pipeline scheduling improvements, code refactors, and a configuration adjustment for Xiangshan to evaluate optimization behavior. Resulting changes enable faster experimentation with scheduling strategies and clearer code paths, aligning with business goals of higher throughput, lower latency, and easier maintenance.

June 2025 — OpenXiangShan/GEM5: Delivery across stability, performance, and test infrastructure with clear business value. Key features delivered include substantial O3 CPU core stability and scheduling improvements, complemented by targeted performance enhancements and CI/testing enhancements. Major bugs fixed include correctness-related fixes in rename handling, stall checks, asymmetric memory IQ layout, and crob/stuck scenarios, reducing simulation stalls and improving reliability. Overall impact: higher correctness, reduced stall cycles, and faster, more reliable benchmarking and validation. Technologies/skills demonstrated include C++/system-level engineering in GEM5, microarchitectural optimization (O3), CPU prediction and ROB tuning, and CI/difftest integration and performance testing. Top achievements reflect strong emphasis on reliability, performance, and testing readiness, enabling faster iteration and more trustworthy performance analyses.

May 2025 (OpenXiangShan/GEM5) delivered significant improvements to vector validation, build flexibility, and architectural correctness, with a strong emphasis on reliable CI, broader RVV support, and performance-oriented scheduler enhancements. The work reduced risk in vector workloads, accelerated validation cycles, and expanded capabilities for production-grade vector workloads across builds and tests.

April 2025 monthly summary focusing on delivering core features, stabilizing CPU models, improving observability, and code quality across GEM5, XiangShan, and Utility repositories. Highlights include performance and correctness improvements in the KMHV3 O3 model, cache/dispatch tuning for KMHV3, a bug fix for issue queue port handling, introduction of instruction lifetime tracing with performance analysis tooling, and code cleanliness improvements.

March 2025 performance-focused sprint across the OpenXiangShan repositories. Delivered substantial improvements to the GEM5 O3 CPU model, expanded memory operation granularity, and strengthened performance analysis capabilities. Key business value includes improved throughput, reduced FP stalls, finer memory scheduling, and faster diagnosis for optimization. The work also advanced stability and observability across the project with targeted fixes and tooling refinements.

February 2025 monthly summary for GEM5 (OpenXiangShan). Delivered RTL-aligned enhancements to the O3 CPU and memory subsystem, along with targeted bug fixes. Key features include compressed/Grouped ROB, memory timing/latency refinements, FP latency modeling, decoupled physical register release, and DRRIP cache timing sampling. Major fixes include restoring vector instruction semantics and improving perf counter reliability. Overall impact: improved RTL accuracy and timing fidelity, reduced memory footprint in ROB, more realistic cache behavior, and more reliable performance metrics to enable faster design-space exploration and better decision-making in RTL optimization.

January 2025: Delivered targeted enhancements to the OpenXiangShan/GEM5 model to improve performance visibility, modeling accuracy, and reliability. Implemented memory subsystem timing and LSU/LSQ improvements to reveal stalls and retries, added fetch/issue statistics and recovery tracking, and fixed diff-testing mcycle handling to ensure correct CSR interpretation. These changes, validated by the included commits, reduce debugging time and provide more trustworthy simulation data for performance tuning and architectural exploration.

December 2024 monthly summary for OpenXiangShan/GEM5. Delivered targeted improvements to the O3 CPU pipeline and memory subsystem, along with hardened performance visibility, driving better throughput, model fidelity, and observability. Key achievements include the following feature and bug work delivered: - O3 CPU instruction scheduling and register file handling improvements: refined register arbitration, writeback handling, forwarding, and fetch/retry logic to reduce stalls and improve CPU model accuracy, enabling higher instruction throughput. - Cache and memory subsystem optimizations (slicing, buses, latency, CDP): implemented non-piped L2/L3 caches with cache slicing, aligned latency with new bus classes, enabled CDP by default, and refined prefetcher integration to boost parallelism and overall system throughput. - Performance monitoring visualization reliability: fixed perfcct visualization logic for identical or zero records and added overflow checks to ensure accurate performance data displays, improving observability and confidence. Overall impact and accomplishments: - Substantial increases in instruction throughput and CPU model fidelity, with clearer observability into performance behavior. - Higher system throughput and better resource utilization through advanced cache design and CDP-enabled data sharing. - Improved reliability of performance dashboards, reducing risk of misinterpretation from edge-case data. Technologies/skills demonstrated: - CPU pipeline optimization (register arbitration, writeback, bypass networks), fetch/retry handling. - Memory hierarchy redesign (non-piped L2/L3, cache slicing, latency alignment, CDP integration, prefetcher tuning). - Performance instrumentation and tooling reliability (perfcct, data accuracy checks). - Configuration management and default enablement of advanced features (CDP), with attention to compatibility and validation.

Month: 2024-11 — OpenXiangShan/GEM5 monthly performance summary. Key accomplishments include delivering O3 CPU Core Scheduling and Performance Modeling Enhancements and fixing O3 CPU Issue Queue Dependency Correctness. These efforts improved scheduling accuracy, reduced potential stalls, and enhanced instrumentation for performance analysis, enabling more reliable performance projections and optimization decisions for GEM5.

October 2024 — OpenXiangShan/GEM5: Delivered memory subsystem enhancements aligned with KMH and a focused O3 LSQ bug fix, driving performance predictability and configurability. Key outcomes include KMH-aligned prefetcher controls and improved collision detection accuracy in the O3 Load-Store Queue. These changes reduce manual tuning needs and improve memory access efficiency across workloads.