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A cache-aware CPU attention kernel gave up to a 2.01x prefill speedup and cut Llama-3.1-8B time-to-first-token by up to 1.74x inside SGLang

AspireAI community · arXiv
Agentic workloads pile concurrent long-context prefills onto the same GPU, and CPUs are a viable alternative once GPU compute is saturated - but existing CPU attention kernels do not adapt to multi-tier cache hierarchies and schedule threads poorly. CACPU combines tiered cache blocking with an in-kernel task dispatching mechanism for causal full-sequence prefilling, reaching up to a 2.01x speedup over PyTorch SDPA, FlexAttention and SGLang attention kernels. Integrated into SGLang, it reduced the time to first token of Llama-3.1-8B by up to 1.74x while preserving model accuracy. The paper is labelled a preprint, and the headline figures are best-case measurements rather than averages across workloads.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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