PDScope decoupled prefill from decode for MoE models on CPU-GPU nodes, lifting prefill throughput 2.5 to 10.3x and decode 2.1 to 6.1x
AspireAI community · arXiv (PPoPP'27)
When a mixture-of-experts model runs locally with limited GPU memory, most experts sit in CPU memory, and prefill and decode pull in opposite directions - prefill wants aggressive GPU loading, decode wants conservative PCIe transfers - so a phase-agnostic scheduler stalls one to serve the other. PDScope observes that expert routing is predictable in phase-specific ways and uses that to schedule and execute the two phases independently, compiling the decisions into overhead-free pipelines using a static computation graph, cache prefetching and zero-copy asynchronous I/O. On mainstream MoE models it achieved 2.5-10.3x higher prefill throughput and 2.1-6.1x higher decode throughput than existing systems, and the authors report it extends naturally to multi-batch settings. The measurements are on specific MoE models and node configurations rather than a general serving fleet.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.