August 11th, 2024

Tree Attention: Topology-Aware Decoding for Long-Context

The paper presents a new algorithm for efficient self-attention in transformers, achieving up to 8x faster decoding on GPU clusters while reducing communication volume and memory usage. Code is publicly available.

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Tree Attention: Topology-Aware Decoding for Long-Context

The paper titled "Tree Attention: Topology-aware Decoding for Long-Context Attention on GPU clusters" addresses the computational challenges associated with self-attention mechanisms in transformer architectures, which exhibit quadratic complexity relative to sequence length. The authors derive a scalar energy function that facilitates the computation of self-attention blocks, providing a theoretical foundation and a Bayesian interpretation linked to energy-based models like Hopfield Networks. They propose a novel algorithm that employs tree reduction for parallelizing attention computation across multiple GPUs, achieving significant performance improvements. Their method reportedly performs cross-device decoding up to eight times faster than existing techniques such as Ring Attention, while also reducing communication volume and peak memory usage by half. The authors have made their code publicly available, contributing to the accessibility of their research.

- The paper introduces a new algorithm for efficient self-attention computation in transformers.

- It provides a theoretical basis for self-attention through a scalar energy function.

- The proposed method allows for up to 8x faster decoding on GPU clusters compared to existing methods.

- The algorithm reduces communication volume and peak memory requirements significantly.

- The authors have made their code publicly accessible for further research and application.

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Link Icon 5 comments
By @mjburgess - 8 months
I recall reading recently that someone went back and trained an RNN at a similar scale to a GPT and got similar performance on modern hardware (perhaps someone can link me that paper?).

ie., the innovation in statistical AI isn't in making the algorithms "smarter", it's finding ways to align the computation with modern GPU hardware -- this has been the story since 2012.

In the end, the function all such algs are approximating is a conditional probability. ie., the perfect answer to any prompt is to ignore training entirely, and at inference time, compute an expectation across all historical data. All training does is essentially optimally cache a large part of that computation.

This is very different to how it's typically sold/understood, in the sense that there's an appearance that at inference-time some unbounded computation is going on, ie., "thinking"/"reasoning"/etc. But at inference time for any prompt the same amount of computation is used, regardless of the question complexity. So the system will appear to reason (etc.) if it can sample convincingly from its pre-cached computation.

This means "innovation" here follows a moore's law S-curve for GPU hardware.

By @brrrrrm - 8 months
how does this approach differ from Nvidia's 2019 writeup on using trees to improve allreduce operations? https://developer.nvidia.com/blog/massively-scale-deep-learn...
By @tveita - 8 months
The same authors also have a language model at https://github.com/Zyphra/Zamba2 but it's not clear to me if that model is connected to tree attention.

The announcement at https://www.zyphra.com/post/zamba2-small links to this paper, but the paper doesn't actually mention Zamba2 anywhere.

By @Narhem - 8 months
How often do papers like this make it to industry applications/published research. Seems stuck in between the two.
By @cs702 - 8 months
Interesting.

The authors claim this outperforms Ring Attention for distributed computation of self-attention over multiple GPUs.

Distributing computation is necessary whenever context is too long for self-attention's computation to fit in a single GPU's available memory.

Github link: https://github.com/Zyphra/tree_attention