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Jonathan Clohessy

PROFILE

Jonathan Clohessy

Worked across ONNX Runtime, XNNPACK, and ROCm/onnxruntime repositories to deliver high-performance matrix multiplication and quantization improvements for machine learning inference. Focused on optimizing ARM NEON and SME microkernels using C and C++, introducing new GEMM and convolution paths, and refining memory management for reliability and speed. Enhanced test coverage and debugging instrumentation, stabilized CI by addressing edge cases in quantized and fastmath kernels, and improved cache efficiency for convolution workloads. Leveraged CMake for build integration and maintained code quality through targeted bug fixes, regression tests, and conditional compilation, enabling robust, production-ready performance across diverse embedded and server platforms.

Overall Statistics

Feature vs Bugs

56%Features

Repository Contributions

21Total
Bugs
7
Commits
21
Features
9
Lines of code
3,150
Activity Months7

Work History

June 2026

1 Commits

Jun 1, 2026

June 2026 monthly summary for ROCm/onnxruntime focused on ARM64 matrix multiply reliability in fastmath. The work clarified and stabilized the ARM64 fastmath path for MatMul, safeguarding numerical correctness and improving test stability across CI. Key achievements: - Fixed corner-case for fastmath SGEMM (K-tail) where K is not a multiple of 4; implemented fallback to a safer SGEMM path to prevent overreads and NaN propagation in NEON fastmath. Commit: e0d99e27b916da2e98f9bb7141c7f1356cf15d9d. - Maintained performance benefits for aligned K by preserving BF16 fastmath where safe, while ensuring correctness for unsafe K-tail cases. - Added regression coverage to guard the MatMul fastmath corner case: onnxruntime_provider_test regression test for MatMulFloatTypeFastMathKTailFallsBackToSgemm. - Expanded test validation across the pipeline (onnxruntime_test_all, QDQTransformerTests) with repeated runs to ensure stability in KleidiAI-enabled and --no_sve configurations. - Result: Reduced flaky test failures and increased reliability of matrix multiply on ARM64, delivering business value through more consistent numeric results and CI stability. Technologies/skills demonstrated: - ARM64 NEON SBGEMM fastmath path, BF16 fastmath, SGEMM, K-tail handling - C++/CI test friction handling and regression testing - Google Test framework, test harness validation, and cross-configuration CI (KleidAI, --no_sve)

May 2026

1 Commits

May 1, 2026

Month: 2026-05, ROCm/onnxruntime. Implemented a critical fix to LHS indirection cache in convolution paths to curb unbounded memory growth and improve stability under varying input tensors. The change removes input-content hashing from the LHS cache key and adds tests to verify cache reuse based on geometry rather than input tensors. This work is anchored by commit 19f5d413fc6f2c8ac06c4d1c65e4371fd7bdd8da and addresses the memory growth observed in issue #28363.

February 2026

4 Commits • 1 Features

Feb 1, 2026

February 2026 monthly summary for CodeLinaro/onnxruntime focusing on KleidiAI kernel performance, reliability, and logging enhancements, plus a critical bug fix for dynamic QGEMM pack B size. Delivered performance optimizations, expanded test coverage, and improved kernel maintainability, enabling faster and more reliable model inference across workloads.

December 2025

5 Commits • 3 Features

Dec 1, 2025

2025-12 Performance Summary: Delivered high-impact performance and maintainability improvements across two key codebases (google/XNNPACK and intel/onnxruntime) with ARM SME2-optimized microkernels and GEMV-based SGEMM paths. The month centered on delivering concrete capabilities with clear business value: faster inference times on targeted workloads, easier cross-architecture integration, and stronger debugging/observability. Key outcomes include introducing an IGEMM PF32 microkernel for ARM SME2 in XNNPACK with a packing variant and initialization logging; refactoring KleidiAI microkernel integration to streamline conditional compilation for SME1/SME2; and adding a high-performance SGEMM path for single-row/column cases in ONNX Runtime using GEMV kernels with a microkernel interface to simplify SME1/SME2 adoption. These changes were supported by build integration, debug logging, and instrumentation improvements, enabling more predictable performance and easier future enhancements. Overall impact: tangible speedups in targeted GEMV/SGEMM workloads, reduced integration complexity across microkernels, and better developer productivity through instrumentation and cleaner conditional compilation. Technologies/skills demonstrated: ARM SME2 packing variants, initialization/logging instrumentation, conditional compilation refactors, GEMV-based SGEMM implementation, microkernel interface design, and performance benchmarking across two leading ML runtimes.

November 2025

3 Commits • 2 Features

Nov 1, 2025

Concise monthly summary for Nov 2025 highlighting performance improvements, configurability enhancements, and stability gains across ONNX Runtime and XNNPACK. Focused on delivering business value through faster dynamic quantization paths, greater runtime flexibility, and robust test coverage to reduce risk in production deployments.

October 2025

6 Commits • 3 Features

Oct 1, 2025

October 2025 performance summary for google/XNNPACK and intel/onnxruntime. Delivered key performance and compatibility improvements across ARM-based targets, with a focus on FP16 optimization, SME-accelerated GEMMs, and build/test stability. Emphasized business value through throughput gains, reduced memory overhead, and broader platform readiness.

August 2025

1 Commits

Aug 1, 2025

August 2025: ONNX Runtime – Quantization correctness and test-stability improvements. Delivered a targeted correctness fix for DynamicQuantizeMatMul and Attention3D by preventing invalid B scales and correctly handling GEMM edge cases in tests. The change reduces test flakiness and fortifies quantized inference reliability, aligning with production quality goals for quantized models.

Activity

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Quality Metrics

Correctness92.0%
Maintainability82.8%
Architecture87.2%
Performance88.6%
AI Usage29.6%

Skills & Technologies

Programming Languages

CC++CMakeYAML

Technical Skills

ARM NEONC programmingC++C++ developmentC++ programmingCMakeCPU optimizationConditional compilationEmbedded SystemsKernel developmentLogging implementationMachine LearningMatrix multiplicationMemory ManagementMicrokernel architecture

Repositories Contributed To

5 repos

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

google/XNNPACK

Oct 2025 Dec 2025
3 Months active

Languages Used

CC++YAMLCMake

Technical Skills

C++ developmentConditional compilationTesting frameworksalgorithm optimizationembedded systemslow-level programming

intel/onnxruntime

Oct 2025 Dec 2025
3 Months active

Languages Used

C++

Technical Skills

ARM NEONC++C++ developmentEmbedded SystemsMemory ManagementPerformance Optimization

CodeLinaro/onnxruntime

Feb 2026 Feb 2026
1 Month active

Languages Used

C++

Technical Skills

C++C++ developmentC++ programmingKernel developmentLogging implementationMachine Learning

ROCm/onnxruntime

May 2026 Jun 2026
2 Months active

Languages Used

C++

Technical Skills

C++ developmentperformance optimizationunit testingCPU optimizationMatrix multiplicationPerformance tuning

microsoft/onnxruntime

Aug 2025 Aug 2025
1 Month active

Languages Used

C++

Technical Skills

C++ developmentalgorithm optimizationmachine learning