用铁电存储器实现高效紧凑的贝叶斯推断,无需额外计算电路。
FeBiM: Efficient and Compact Bayesian Inference Engine Empowered with Ferroelectric In-Memory Computing
- 将量化对数概率映射到铁电晶体管状态,直接在存内完成推断
- 在典型分类任务中达26.32 Mb/mm²密度和581.40 TOPS/W能效
- 相比现有硬件方案,紧凑性提升10.7倍,效率提升43.4倍
在训练数据有限或需可解释性的场景下,传统神经网络模型常面临挑战。相比之下,基于贝叶斯推断的算法在提供可解释预测与可靠不确定性估计方面表现优异。尽管当前先进的存内计算(IMC)架构利用新兴非易失性存储(NVM)技术,在神经网络负载中展现出卓越的计算能力与能效,但其在贝叶斯推断中的应用受限。这是因为贝叶斯推断的核心操作与神经网络常见的乘加(MAC)运算差异显著,难以直接适配多数现有IMC设计。本文提出FeBiM,一种基于多比特铁电场效应晶体管(FeFET)的高效紧凑贝叶斯推断引擎。FeBiM将训练好的贝叶斯模型概率编码于小型FeFET交叉阵列中,通过将量化对数概率映射至离散的FeFET状态,使交叉阵列的累加输出自然表示后验概率——即给定观测值下的贝叶斯推断结果。该方法无需额外计算电路即可实现高效的存内贝叶斯推断。作为首个基于FeFET的存内贝叶斯推断引擎,FeBiM在典型分类任务中实现了26.32 Mb/mm²的存储密度与581.40 TOPS/W的计算能效,相较现有最优硬件实现,紧凑性提升10.7倍,能效提升43.4倍。
原文摘要 · Abstract (English)
In scenarios with limited training data or where explainability is crucial, conventional neural network-based machine learning models often face challenges. In contrast, Bayesian inference-based algorithms excel in providing interpretable predictions and reliable uncertainty estimation in these scenarios. While many state-of-the-art in-memory computing (IMC) architectures leverage emerging non-volatile memory (NVM) technologies to offer unparalleled computing capacity and energy efficiency for neural network workloads, their application in Bayesian inference is limited. This is because the core operations in Bayesian inference differ significantly from the multiplication-accumulation (MAC) operations common in neural networks, rendering them generally unsuitable for direct implementation in most existing IMC designs. In this paper, we propose FeBiM, an efficient and compact Bayesian inference engine powered by multi-bit ferroelectric field-effect transistor (FeFET)-based IMC. FeBiM effectively encodes the trained probabilities of a Bayesian inference model within a compact FeFET-based crossbar. It maps quantized logarithmic probabilities to discrete FeFET states. As a result, the accumulated outputs of the crossbar naturally represent the posterior probabilities, i.e., the Bayesian inference model's output given a set of observations. This approach enables efficient in-memory Bayesian inference without the need for additional calculation circuitry. As the first FeFET-based in-memory Bayesian inference engine, FeBiM achieves an impressive storage density of 26.32 Mb/mm$^{2}$ and a computing efficiency of 581.40 TOPS/W in a representative Bayesian classification task. These results demonstrate 10.7$\times$/43.4$\times$ improvement in compactness/efficiency compared to the state-of-the-art hardware implementation of Bayesian inference.
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