What problem does it solve?
Large-sequence transformer attention consumes O(N²) memory and can cause GPU out-of-memory errors and slow training/inference for contexts beyond a few hundred tokens. This Skill guides engineers to replace standard attention with Flash Attention or PyTorch's native SDPA to drastically reduce memory footprint and accelerate attention computation.
Core Features & Use Cases
- Memory-efficient attention: Eliminates materializing the full attention matrix to cut memory usage by an order of magnitude for long contexts.
- Speed improvements: Typical 2-4x speedup for sequences >512 tokens and higher gains on H100 with FP8.
- Compatibility & advanced modes: Instructions for PyTorch native SDPA (2.2+), the flash-attn library for sliding windows and multi-query attention, and FP8/H100 optimizations.
- Practical workflows: Checklists for integrating into existing models, benchmarking guidance, and troubleshooting tips for common CUDA and dtype issues.
- Use case examples: training large models with long context, serving long-context inference, and enabling sliding-window or paged KV caches.
Quick Start
Enable Flash Attention by switching your model's attention implementation to PyTorch's scaled_dot_product_attention or installing and calling the flash-attn library on CUDA tensors.