Non-Monotonic Latency in Apple MPS Decoding: KV Cache Interactions and Execution Regimes
Autoregressive inference is typically assumed to scale predictably with decoding length, with latency increasing smoothly as generated sequence length grows. In this work, we identify unexpected non-monotonic latency behavior in the Apple MPS backend, where latency changes abruptly across nearby decoding configurations during transformer decoding. Using multiple model families (GPT-2, BLOOM, and OPT), we observe latency spikes of up to 21x within specific decoding-budget intervals, followed by recovery at neighboring configurations. Controlled experiments show that these anomalies originate primarily during the decode phase rather than prefill, are not explained by memory pressure alone, ...
| Authors | Willy Fitra Hendria |
|---|---|
| Primary category | cs.LG |
| Published | 9 May 2026 |
| Last updated at source | 14 May 2026 |
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