PIMPAL: Accelerating LLM Inference on Edge Devices via In-DRAM Arithmetic Lookup

Deploying Large Language Models (LLMs) on edge devices poses significant challenges due to their high computational and memory demands. In particular, General MatrixVector Multiplication (GEMV), a key operation in LLM inference, is highly memory-intensive, making it difficult to accelerate using conventional edge computing systems. While Processing-in-memory (PIM) architectures have emerged as a promising solution to this challenge, they often suffer from high area overhead or restricted computational precision. This paper proposes PIMPAL (Processing-In-Memory architecture with Parallel Arithmetic Lookup), a cost-effective PIM architecture leveraging LookUp Table (LUT)-based computation for GEMV acceleration in sLLMs (small LLMs). By replacing traditional arithmetic operations with parallel in-DRAM LUT lookups, PIMPAL significantly reduces area overhead while maintaining high performance. PIMPAL introduces three key innovations: (1) it divides DRAM bank subarrays into compute blocks for parallel LUT processing; (2) it employs Localityaware Compute Mapping (LCM) to reduce row activations by maximizing LUT access locality; and (3) it enables multi-precision computations through a LUT Aggregation (LAG) mechanism that combines results from multiple small LUTs. Experimental results show that PIMPAL achieves up to $17.8 x$ higher performance than previous LUT-based PIM designs and reduces area overhead by $40 \%$ compared to conventional processing unit-based PIM designs.