arXiv:1911.02150cs.NE
Fast Transformer Decoding: One Write-Head is All You Need
Abstract
Multi-head attention layers, as used in the Transformer neural sequence model, are a powerful alternative to RNNs for moving information across and between sequences. While training these layers is generally fast and simple, due to parallelizability across the length of the sequence, incremental inference (where such paralleization is impossible) is often slow, due to the memory-bandwidth cost of repeatedly loading the large "keys" and "values" tensors. We propose a variant called multi-query attention, where the keys and values are shared across all of the different attention "heads", greatly reducing the size of these tensors and hence the memory bandwidth requirements of incremental decoding. We verify experimentally that the resulting models can indeed be much faster to decode, and incur only minor quality degradation from the baseline.
>Autoregressive decoder inference is a severe bottleneck for Transformer models due to the memory bandwidth overhead from loading decoder weights and all attention keys and values at every decoding step (Shazeer, 2019; Pope et al., 2022; de Jong et al., 2022). The memory…
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This is the original paper: https://arxiv.org/abs/1911.02150 . The idea is that with a transformer you have many heads, say 64 for LLaMa, and for each head you have 1 "query" vector one "key" vector and one "value" vector per token. Most of the cost of inferencing models is…
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