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Simon Fan

PROFILE

Simon Fan

Worked extensively on the pytorch/torchtitan repository, delivering advanced features and stability improvements for distributed deep learning and expert-parallelism. Focused on optimizing MoE model compilation, CUDA performance, and device mesh parallelism, using Python, CUDA, and PyTorch. Addressed graph break issues, enhanced recomputation determinism, and introduced experimental AutoParallel features for scalable training. Improved CI workflows, code quality, and local development by refining linting and unit testing practices. Delivered targeted bug fixes for compilation and synchronization, while collaborating across teams to align on graph transforms and performance testing. The work emphasized robust, reproducible model training and efficient parallel computing for large-scale workloads.

Overall Statistics

Feature vs Bugs

67%Features

Repository Contributions

21Total
Bugs
5
Commits
21
Features
10
Lines of code
4,790
Activity Months8

Work History

June 2026

4 Commits • 3 Features

Jun 1, 2026

June 2026 monthly summary for pytorch/torchtitan: Focused on advancing scalable expert-parallelism and robust performance measurement. Delivered MinimalAsyncEP integration for CUDA with a minimal kernel footprint and compatibility updates; introduced Syncless EP improvements (FusedGroupedExperts override and offset-aware SwiGLU) to boost efficiency for MinimalAsyncEP and HybridEP; refined performance testing by enforcing a minimum of 10 iterations to improve measurement reliability and reduce skew. These efforts contributed to higher training throughput, lower per-iteration variance, and smoother onboarding for advanced parallelism configurations.

May 2026

2 Commits • 1 Features

May 1, 2026

May 2026: Focused on enhancing performance and stability of the Repeat-Interleave path in torchtitan for distributed training workloads. Delivered CUDA-level optimizations and a necessary stability rollback to ensure correctness across CPU-CUDA synchronization paths.

March 2026

3 Commits

Mar 1, 2026

Month 2026-03: Focused on stabilizing the Inductor compilation pathway in pytorch/torchtitan to improve reliability and scalability for large-model experiments. Delivered targeted fixes to the full_inductor_compilation workflow, reducing crash risk and ensuring consistent behavior across side-effectful models and complex graph transforms.

January 2026

2 Commits • 2 Features

Jan 1, 2026

Month: 2026-01 — Focused on advancing parallelism capabilities and improving local development workflow in pytorch/torchtitan. Delivered two features: (1) Device Mesh Convention Alignment for DeepSeek v3 Parallelism, integrating the new device mesh usage to enhance local_map_deepseek_v3 parallel processing, and (2) Development Workflow Improvement by suppressing Pyrefly lint errors in local development to reduce distractions. No major bugs fixed this period. Overall, these changes improve model parallelism efficiency, developer productivity, and maintainability, while enabling clearer traceability of changes.

December 2025

5 Commits • 2 Features

Dec 1, 2025

For 2025-12, focused on Autoparallel developments in pytorch/torchtitan: delivered dynamic input token marking to reduce recompilations; introduced a local_map variant of DSv3 with 2D mesh AP to improve stability and compatibility with upcoming features; established CI workflows and naming consistency; implemented a one-time patch guard in autoparallel initialization to prevent repeated apply_compile, with new unit tests. These efforts reduce recompile frequency, increase stability, and accelerate experimentation, enabling smoother integration with upcoming PP features.

November 2025

2 Commits • 1 Features

Nov 1, 2025

November 2025: Key contributions to pytorch/torchtitan focused on correctness and distributed training readiness. Delivered a deterministic recomputation graph fix by disabling the Dynamo LRU cache, ensuring the recomputation graph matches the original forward graph for code objects with multiple valid graphs. This improves reproducibility and reliability of compiled graphs, with a manageable overhead due to caching behavior. Landed AutoParallel as an experimental feature in main to enable automatic configuration of distributed training parallelism layouts based on device mesh analysis, accelerating experimentation with distributed strategies and enabling collaboration across related workstreams (SimpleFSDP, Compiler Toolkit, and Autoparallel).

October 2025

1 Commits

Oct 1, 2025

October 2025 focused on stabilizing large MoE support in torchtitan under challenging graph-break scenarios when using torch.compile and auto-casting (AC). Implemented a targeted workaround to compile MoE layers without triggering graph breaks, by wrapping specific submodules rather than the entire MoE block. This preserves model functionality and reduces tracing-induced regressions in production-like configurations.

August 2025

2 Commits • 1 Features

Aug 1, 2025

August 2025 focused on stabilizing and accelerating MoE workloads in torchtitan. Delivered key MoE compilation stability and performance improvements, including refactoring to avoid static method nested graph breaks, introduction of expert-parallel functions for training throughput, and optimization of grouped GEMM tensor ops. Also stabilized MoE workflow by disabling capture_scalar_outputs by default to prevent hangs in the PyTorch MoE path. These changes reduce training instability, increase throughput, and enable more reliable scaling of MoE models.

Activity

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Quality Metrics

Correctness88.6%
Maintainability81.0%
Architecture83.8%
Performance81.8%
AI Usage37.2%

Skills & Technologies

Programming Languages

MarkdownPythonYAML

Technical Skills

CUDACode QualityContinuous IntegrationDeep LearningDevOpsDistributed SystemsGraph Neural NetworksLintingMachine LearningModel OptimizationParallel ComputingPyTorchPythonPython DevelopmentUnit Testing

Repositories Contributed To

2 repos

Overview of all repositories you've contributed to across your timeline

pytorch/torchtitan

Oct 2025 Jun 2026
7 Months active

Languages Used

PythonYAMLMarkdown

Technical Skills

Deep LearningMachine LearningModel OptimizationPyTorchPythondistributed systems

huggingface/torchtitan

Aug 2025 Aug 2025
1 Month active

Languages Used

Python

Technical Skills

Deep LearningMachine LearningModel OptimizationParallel ComputingPyTorch