TL;DR: Organize your neurons into a tree to get 78x faster inference (theoretical limit is 341x).
This was demonstrated on BERT-base, where this change preserved 96% of its downstream GLUE performance. For a quick comparison, DistilBERT offers 1.6x acceleration while preserving 97% of GLUE performance.
This is a HuggingFace Featured Paper from 11/21/2023.
Paper: https://arxiv.org/abs/2311.10770
Code: https://github.com/pbelcak/UltraFastBERT
Model: https://huggingface.co/pbelcak/UltraFastBERT-1x11-long
Abstract:
Language models only really need to use an exponential fraction of their neurons for individual inferences.
As proof, we present UltraFastBERT, a BERT variant that uses 0.3% of its neurons during inference while performing on par with similar BERT models. UltraFastBERT selectively engages just 12 out of 4095 neurons for each layer inference. This is achieved by replacing feedforward networks with fast feedforward networks (FFFs).
While no truly efficient implementation currently exists to unlock the full acceleration potential of conditional neural execution, we provide high-level CPU code achieving 78x speedup over the optimized baseline feedforward implementation, and a PyTorch implementation delivering 40x speedup over the equivalent batched feedforward inference.
We publish our training code, benchmarking setup, and model weights.
This exponential acceleration was achieved on a 180mn BERT model. Just imagine how amazing the speedup would be on a multi-bn parameter model such as LLaMA if the tree trick (i.e. "fast feedforward networks") continues to scale up to larger layer sizes...
As someone who writes CUDA code professionally, these are my two cents on the matter: The reported speed enhancements, particularly the claimed 117.83x speedup, might be somewhat misleading. Consider, for example, the comparison of CUDA speedups. The authors contrast their CUDA Fast Feed Forward (CUDA fff) implementation with their own highly unoptimized version of a CUDA Fast Forward (CUDA ff).
In an effort to ensure a fair comparison, they maintained the same code structure for both CUDA fff and CUDA ff. However, this approach resulted in the CUDA ff not utilizing any shared memory and caused significant memory divergence due to the use of threadIdx.x for indexing the outer dimensions of matrices.
If you compare the best implementation of FFF on CUDA to the best implementation of FF on CUDA, then the speed-up they got is 3.15x:
See Page 5 Further comparisons: "On GPU, the PyTorch BMM implementation of FFF delivers a 3.15x speedup over the fastest (Native fused) implementation of FF"
The 40x that u/lexected mentioned seems to apply only when comparing to an apparently much slower FF version.
It's a pretty cool paper regardless, as far as I can tell from skimming it. But it could benefit from stating more clearly what has been achieved.