TL;DR

Distributed training splits work across GPUs/machines: data parallelism (different data, same model), model parallelism (split model across devices), or pipeline parallelism (different layers on different devices).

Parallelism strategies

Data parallelism: Each GPU has full model, processes different data batches. Most common, easiest to implement.

Model parallelism: Model split across GPUs (layers or tensor-wise). Needed for models too large for one GPU.

Pipeline parallelism: Split model into stages, process micro-batches through pipeline. Reduces bubble time.

Implementation frameworks

  • PyTorch Distributed (DDP, FSDP)
  • DeepSpeed (ZeRO optimization)
  • Megatron-LM (Nvidia)
  • Ray Train

Best practices

  • Start with data parallelism
  • Use gradient accumulation for effective larger batches
  • Monitor GPU utilization
  • Optimize data loading to prevent bottlenecks