Distributed Training

How Does Distributed Training Work?

Distributed training strategies primarily fall into two categories, which can also be used in combination:

• Data Parallelism: This is the most common approach. In this strategy, the entire model is replicated on each worker (or GPU). The main training dataset is split into smaller chunks, and each worker is assigned a chunk. Each worker independently computes the forward and backward passes for its data subset to generate gradients. These gradients are then aggregated and averaged, typically through a process like All-Reduce, and the consolidated gradient is used to update the model parameters on all workers. This ensures that every copy of the model remains synchronized.
• Model Parallelism: This strategy is used when a model is too large to fit into the memory of a single GPU. Here, the model itself is partitioned, with different layers or sections placed on different workers. Data is passed between workers as it flows through the layers of the neural network. This approach is more complex to implement due to the high communication demands between workers but is essential for training massive models like foundation models. Architectures like Mixture of Experts (MoE) rely heavily on model parallelism.

Real-World Applications

Distributed training is fundamental to many modern AI breakthroughs.

1. Training Large-Scale Vision Models: Companies developing advanced computer vision models, such as Ultralytics YOLO11, often use massive datasets like COCO or ImageNet. Using data parallelism, they can distribute the training across a cluster of GPUs. This drastically cuts down training time from weeks to just hours or days, enabling faster iteration, more extensive hyperparameter tuning, and ultimately leading to models with higher accuracy.
2. Developing Large Language Models (LLMs): The creation of LLMs like those in the GPT series would be impossible without distributed training. These models contain hundreds of billions of parameters and cannot be trained on a single device. Researchers use a hybrid approach, combining model parallelism to split the model across GPUs and data parallelism to process vast amounts of text data efficiently. This is a core component of projects like NVIDIA's Megatron-LM.

Distributed Training vs. Related Concepts

It's important to distinguish distributed training from other related terms:

• Federated Learning: While both involve multiple devices, their goals and constraints differ. Distributed training is typically performed in a controlled environment like a data center with high-speed connections to accelerate training for a single entity. In contrast, federated learning trains models on decentralized devices (e.g., smartphones) without moving the private data to a central server. The primary focus of federated learning is data privacy, whereas for distributed training, it is speed and scale.
• Edge AI: These terms refer to different stages of the ML lifecycle. Distributed training is part of the training phase. Edge AI concerns the deployment phase, where an optimized model runs inference directly on a local, often resource-constrained, device like a camera or a car's onboard computer. A model trained using distributed methods may be prepared for Edge AI deployment.

Tools and Implementation

Implementing distributed training is facilitated by various tools and platforms:

• ML Frameworks: Core frameworks like PyTorch and TensorFlow provide built-in support for distributed training APIs, such as PyTorch DistributedDataParallel and TensorFlow's tf.distribute.Strategy.
• Specialized Libraries: Libraries like Horovod, developed by Uber, offer a framework-agnostic approach to distributed deep learning.
• Cloud Platforms: Major cloud providers like AWS, Google Cloud, and Microsoft Azure offer managed ML services and infrastructure optimized for large-scale distributed training.
• MLOps Platforms: Platforms like Ultralytics HUB simplify the process by providing interfaces for managing datasets, selecting models, and launching training jobs, including cloud training options that handle the underlying distributed infrastructure. Good MLOps practices are key to managing distributed training effectively.