When a model is too large for one GPU, pipeline parallelism splits it vertically into sequential stages on different GPUs. Input data moves from one device to the next until the full model has run, making execution possible rather than merely faster. section 3.3.2 section 3.5
The practical trade-offs are straightforward:
- A naive one-batch pipeline creates a large utilization bubble: while one GPU processes its stage, other GPUs wait. section 3.3.2
- Microbatching reduces the bubble by letting the first GPU forward smaller batches sooner and continue working while later stages process earlier batches. section 3.3.2
- Pipeline parallelism can combine with tensor and data parallelism; together, data, tensor, and pipeline parallelism form 3D parallelism. section 3.5



