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Optimizing LLM Inference with Hardware-Aware Sequence Packing

Towards Data Science •
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Developer AnubhabBanerjee created WarpGroup-Backend, a C++ solution that eliminates GPU waste from zero-padding in LLM inference. Standard batch processing forces GPUs to perform billions of multiplications on padded zeros, consuming compute resources without adding value. This approach transforms variable-length sequences into efficient packed batches, dramatically reducing computational waste.

The system achieves 5.89× faster inference on a GTX 1080 and 2.08× on an H100 by implementing VRAM-aware bin packing. Unlike Python-based solutions limited by the GIL, WarpGroup uses C++ to pack sequences like a "very anxious Tetris champion," while handling GPU-specific alignment requirements that often leave throughput on the floor.

The five-phase pipeline measures available VRAM, tokenizes text, packs sequences efficiently, transfers via pinned memory, and executes FlashAttention-2. This approach eliminates OOM crashes and represents a practical solution for production inference stacks that need to maximize GPU utilization while minimizing unnecessary computations.