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arXiv · 2507.18454

Sandwich: Joint Configuration Search and Hot-Switching for Efficient CPU LLM Serving

Juntao Zhao·Jiuru Li·Chuan Wu
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Abstract

CPUs are critical for LLM serving due to their availability, cost efficiency, and edge applicability. However, efficient CPU serving is hindered by conflicting prefill/decode resource demands under non-disaggregated deployment constraints--existing solutions fail to avoid cross-phase interference, ignore sub-NUMA hardware structures, and deliver suboptimal dynamic-shape kernel performance. We propose Sandwich, a full-stack CPU LLM serving system with three core innovations addressing these challenges: (1) seamless phase-wise plan switching to eliminate cross-phase interference; (2) TopoTree, a tree-based hardware abstraction for automated substructure-aware (e.g., LLC slices) partial core allocation; (3) fast-start-then-finetune dynamic-shape tensor program generation. Across five x86/ARM CPU platforms, Sandwich achieves an average 2.01x end-to-end speedup and up to 3.40x latency reduction over state-of-the-art systems. Its kernels match static compiler performance with three orders of magnitude lower tuning cost.

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Juntao Zhao, Jiuru Li, Chuan Wu. 2025-05-19. Sandwich: Joint Configuration Search and Hot-Switching for Efficient CPU LLM Serving. https://doi.org/10.1145/3770743.3803931

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