Tree-based machine learning performed in-memory with memristive analog CAM

• Published in: Nature communications Vol. 12; no. 1; p. 5806
• Main Authors: Pedretti, Giacomo, Graves, Catherine E., Serebryakov, Sergey, Mao, Ruibin, Sheng, Xia, Foltin, Martin, Li, Can, Strachan, John Paul
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.10.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 639/166/987; 639/925/927/1007; Algorithms; Artificial neural networks; Associative memory; Computer applications; Datasets; Decision trees; Humanities and Social Sciences; Inference; Learning algorithms; Lookup tables; Machine learning; Memristors; multidisciplinary; Neural networks; Science; Science (multidisciplinary)
• DOI: 10.1038/s41467-021-25873-0
• ISSN: 2041-1723

Tree-based machine learning techniques, such as Decision Trees and Random Forests, are top performers in several domains as they do well with limited training datasets and offer improved interpretability compared to Deep Neural Networks (DNN). However, these models are difficult to optimize for fast inference at scale without accuracy loss in von Neumann architectures due to non-uniform memory access patterns. Recently, we proposed a novel analog content addressable memory (CAM) based on emerging memristor devices for fast look-up table operations. Here, we propose for the first time to use the analog CAM as an in-memory computational primitive to accelerate tree-based model inference. We demonstrate an efficient mapping algorithm leveraging the new analog CAM capabilities such that each root to leaf path of a Decision Tree is programmed into a row. This new in-memory compute concept for enables few-cycle model inference, dramatically increasing 10 3  × the throughput over conventional approaches. Tree-based machine learning algorithms are known to be explainable and effective even trained on limited datasets, however difficult to optimize on conventional digital hardware. The authors apply analog content addressable memory to accelerate tree-based model inference for improved performance.