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tech 11 May 2026

Training an LLM in Swift, Part 1: Taking Matrix Multiplication from Gflop/s to Tflop/s

In this article, learn how to optimize matrix multiplication in Swift to efficiently train a large language model (LLM), moving from Gflop/s to Tflop/s.

Article inspired by the original source
Training an LLM in Swift, Part 1: Taking matrix mult from Gflop/s to Tflop/s ↗ www.cocoawithlove.com

Introduction

Training large language models (LLMs) is a resource-intensive task. To achieve optimal performance, especially on Apple Silicon, mastering matrix multiplication is crucial. This article focuses on optimizing this operation in Swift to move from gigaflops per second (Gflop/s) to teraflops per second (Tflop/s).

Why Swift?

Swift is often underestimated for machine learning applications, dominated by Python and its myriad libraries. However, Swift offers execution speed close to C, while benefiting from modern syntax and type safety. This makes it an ideal choice to explore low-level optimizations.

Understanding the Basics

Matrix multiplication is at the core of computations for neural networks. Simply put, to train an LLM, this operation needs to be performed billions of times. Transforming these calculations from Gflop/s to Tflop/s requires meticulous optimizations, particularly on Apple Silicon processors equipped with CPUs, GPUs, and SIMD units.

Optimization in Swift

Using SIMD

Single Instruction, Multiple Data (SIMD) enables processing multiple data points with a single instruction. In Swift, this translates to using vectors that significantly accelerate matrix calculations.

Leveraging Metal

Metal is Apple's graphics and compute API, designed to harness GPU capabilities. In Swift, integrating Metal for matrix multiplication can exponentially boost performance, potentially reaching Tflop/s.

Multi-threading

Effective use of multi-threading allows distributing computational tasks across multiple CPU cores. Swift offers robust solutions for thread management, maximizing resource utilization.

Case Study: Swift Implementation

Consider a matrix multiplication implementation in Swift. Using the techniques above, it is possible to match or even surpass the performance of a classic C implementation like Andrej Karpathy's llm.c.

Conclusion

Optimizing matrix multiplication in Swift for LLM training is not only feasible but can yield remarkable performance on Apple Silicon. Whether you are a developer or a tech entrepreneur, exploring these optimizations can transform how you approach machine learning on Mac.

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