perf: pad small attention heads to 64 for MMA Flash Attention - #1992
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Summary
Small attention heads, such as SD1.5's 40-channel heads, cannot use CUDA MMA Flash Attention directly. Automatically zero-pad compatible F32 Q/K/V heads below 64 channels to 64 when Flash Attention is enabled and both the CUDA device and compiled backend support MMA.
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Additional Information
14.36it/s -> 16.28it/s
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