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Prefill-decode disaggregation was routing request by request, and DolphinRouting's cluster-level policy cut P90 TTFT by 5.7 to 7.9 percent against Dynamo

AspireAI community · arXiv (DolphinRouting)
Prefill-decode disaggregation splits serving into separate prefill and decode phases, but deciding per request whether to prefill locally or remotely has to account for prefill work, cache reuse and decode demand at the same time. DolphinRouting clusters requests by raw prompt length, cache-adjusted input lengths on both worker pools, and output length, then learns a single binary routing action per cluster offline from end-to-end SLO feedback, with online routing reduced to feature extraction, cluster assignment and a table lookup. Evaluated on a real prefill-decode disaggregated cluster with three public benchmarks, a mixed workload and real data, the k-means variant reduces P90 time-to-first-token by 5.7 to 7.9 percent and P90 time-per-output-token by 2.6 to 10.1 percent relative to Dynamo. The limitation is that the gains are single-digit percentages on one cluster under one prefill-to-decode resource split, and the learned policy has to be retrained for a different allocation.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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.
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