arXiv Computation and Language By Qihang Fan, Huaibo Huang, Zhiying Wu, Bingning Wang, Ran He

FlashPrefill V2: Block-Sparse Prefill Attention for Long-Context LLM Serving

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arXiv:2608. 19758v1 Announce Type: new Abstract: Long-context modeling is a pivotal capability for Large Language Models, yet the quadratic complexity of attention remains a critical bottleneck, particularly during the compute-intensive prefilling phase.

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arXiv Machine Learning
1d ago

FlashAttention for Scalable Vector Architectures

FlashAttention-V is a blocked FlashAttention implementation optimized for scalable vector architectures, designed to reduce the memory bandwidth bottleneck of transformer attention on CPUs. By fusing operations, exploiting parallelism across attention heads, and inter‑head packing, it improves vector register utilization and memory locality, enabling efficient scaling from short to very long vectors. Benchmarks on TinyLlama, Llama 3.2, Qwen2.5, and Pythia‑410M show 22×–42× speedups over scalar FlashAttention in prefill and 8×–11× in decode on a Banana Pi BPI‑F3, while also revealing quantization‑related bottlenecks that limit long‑vector scalability.

By Sonia Rani Gupta, Nikela Papadopoulou, Miquel Peric\`as