FFSplit: Split Feed-Forward Network For Optimizing Accuracy-Efficiency
  Trade-off in Language Model Inference
Zirui Liu Qingquan Song Qiang Charles Xiao Sathiya Keerthi Selvaraj Rahul Mazumder Aman Gupta Xia Hu
The large number of parameters in Pretrained Language Models enhance their
performance, but also make them resource-intensive, making it challenging to
deploy them on commodity hardware like a single GPU. Due to the memory and
power limitations of these devices, model compression techniques are often used
to decrease both the model's size and its inference latency. This usually
results in a trade-off between model accuracy and efficiency. Therefore,
optimizing this balance is essential for effectively deploying LLMs on
commodity hardware. A significant portion of the efficiency challenge is the
Feed-forward network (FFN) component, which accounts for roughly $\frac{2}{3}$
total parameters and inference latency. In this paper, we first observe that
only a few neurons of FFN module have large output norm for any input tokens,
a.k.a. heavy hitters, while the others are sparsely triggered by different
tokens. Based on this observation, we explicitly split the FFN into two parts
according to the heavy hitters. We improve the efficiency-accuracy trade-off of
existing compression methods by allocating more resource to FFN parts with
heavy hitters. In practice, our method can reduce model size by 43.1\% and
bring $1.25\sim1.56\times$ wall clock time speedup on different hardware with
negligible accuracy drop.