LLM fine-tuning on serverless clusters failed 52 percent of the time at small batch sizes and 95 percent at the largest
AspireAI community · arXiv
Serverless operation of LLM fine-tuning shifts operational concerns from the user to the provider, and the workloads bring performance problems, resource waste and outright service failure from misconfiguration. The work characterises how these fine-tuning jobs actually run, analysing IBM's LLMFineTuningBench, a profiling dataset of 30,920 experiments that records successful and failing configurations across four GPU types and setups from 1 to 32 GPUs. Job feasibility depends on workload properties: failure ratios rise from 52 percent for small batch sizes of 16-64 up to 95 percent at the largest batch size of 1,024. Throughput grows logarithmically with batch size, scaling is near-linear intra-node, and RoCE raises inter-node efficiency from 0.26 to 0.72, with system-level optimisations outweighing application-level ones.
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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.