SMoE: An Algorithm-System Co-Design for Pushing MoE to the Edge via Expert Substitution

The Mixture of Experts (MoE) architecture has emerged as a key technique for scaling Large Language Models by activating only a subset of experts per query. Deploying MoE on consumer-grade edge hardware, however, is constrained by limited device memory, making dynamic expert offloading essential. Unlike prior work that treats offloading purely as a scheduling problem, we leverage expert importance to guide decisions, substituting low-importance active experts with functionally similar ones already cached in GPU memory, thereby preserving accuracy. As a result, this design reduces memory usage and data transfer, while largely eliminating PCIe overhead. In addition, we introduce a scheduling policy that maximizes the reuse ratio of GPU-cached experts, further boosting efficiency. Our extensive evaluations show that, compared with state-of-theart approaches, our method achieves a 48% reduction in decoding latency and maintains an expert cache hit rate above 60%, all while preserving nearly lossless accuracy.