T-MAC: CPU Renaissance via Table Lookup for Low-Bit LLM Deployment on
  Edge
Authors: name: Jianyu Wei; name: Shijie Cao; name: Ting Cao; name: Lingxiao Ma; name: Lei Wang; name: Yanyong Zhang; name: Mao Yang
Published: 2024-06-25 08:38:38

Abstract: The deployment of Large Language Models (LLMs) on edge devices is
increasingly important to enhance on-device intelligence. Weight quantization
is crucial for reducing the memory footprint of LLMs on devices. However,
low-bit LLMs necessitate mixed precision matrix multiplication (mpGEMM) of low
precision weights and high precision activations during inference. Existing
systems, lacking native support for mpGEMM, resort to dequantize weights for
high precision computation. Such an indirect way can lead to a significant
inference overhead.
  In this paper, we introduce T-MAC, an innovative lookup table(LUT)-based
method designed for efficient low-bit LLM (i.e., weight-quantized LLM)
inference on CPUs. T-MAC directly supports mpGEMM without dequantization, while
simultaneously eliminating multiplications and reducing additions required.
Specifically, T-MAC transforms the traditional data-type-centric multiplication
to bit-wise table lookup, and enables a unified and scalable mpGEMM solution.
  Our LUT-based kernels scale linearly to the weight bit-width. Evaluated on
low-bit Llama and BitNet models, T-MAC demonstrates up to 4x increase in
throughput and 70% reduction in energy consumption compared to llama.cpp. For
BitNet-b1.58-3B, T-MAC delivers a token generation throughput of 30 tokens/s
with a single core and 71 tokens/s with eight cores on M2-Ultra, and 11
tokens/s on lower-end devices like Raspberry Pi 5, which significantly exceeds
the adult average reading speed. T-MAC with LUT-based computing paradigm, paves
the way for the practical deployment of low-bit LLMs on resource-constrained
edge devices without compromising computational efficiency. The system is
open-sourced at https://github.com/microsoft/T-MAC.