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This research tackles the bottleneck where NVIDIA Blackwell's FP4 tensor cores fail to accelerate attention mechanisms due to softmax conversion overhead and quantization dependencies. The authors propose "Direct-P" for noncausal inference and a novel causal path that integrates forward quantization directly into backward passes, achieving significant throughput gains on GB200 hardware. Crucially, the study identifies training divergence risks with standard MXFP4 probability/value trajectories, offering specific architectural adjustments to maintain stability in large-scale model updates.
Hardware-Aware FP4 FlashAttention-4
arXiv:2609.04105v1 Announce Type: new Abstract: Blackwell's 4-bit floating-point (FP4) tensor cores do not automatically make attention faster because softmax conversion and on-chip dependencies dominate once its matrix products shrink. We address this with \emph{Direct-P} for noncausal inference and a causal path that passes the forward quantization directly into backward. Direct-P maps scores directly to FP4 probabilities and reaches up to 2.13$\times$ the bfloat16 (BF16) forward throughput on an NVIDIA GB200. The causal path reconstructs probabilities from saved quantized queries and keys and uses 8-bit floating-point (FP8) gradient operands, accelerating a complete single-GPU 8-billion-parameter update by up to 1.14$\times$. Matched distributed training retains FP8 probabilities and values; every tested MXFP4 probability/value training trajectory diverges.
Abstract:Blackwell's 4-bit floating-point (FP4) tensor cores do not automatically make attention faster because softmax conversion and on-chip dependencies dominate once its matrix products shrink. We address this with \emph{Direct-P} for noncausal inference and a causal path that passes the forward quantization directly into backward. Direct-P maps scores directly to FP4 probabilities and reaches up to 2.13$\times$ the bfloat16 (BF16) forward throughput on an NVIDIA GB200. The causal path reconstructs probabilities from saved quantized queries and keys and uses 8-bit floating-point (FP8) gradient operands, accelerating a complete single-GPU 8-billion-parameter update by up to 1.14$\times$. Matched distributed training retains FP8 probabilities and values; every tested MXFP4 probability/value training trajectory diverges.
Machine Learning (cs.LG)
arXiv:2609.04105 [cs.LG]
(or arXiv:2609.04105v1 [cs.LG] for this version)
https://doi.org/10.48550/arXiv.2609.04105 Focus to learn more arXiv-issued DOI via DataCite (pending registration)
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