Add repetition penalty to the llm-runner - #176
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tjia1818
August 15, 2026 18:36
Penalizes tokens that appear in recent generation history, discouraging repetitive output. Applied as a separate logit modification step before the existing sampling pipeline (temperature/topK/topP/minP). - Add repetitionPenalty and repetitionPenaltyWindow to SamplingConfiguration - Add RepetitionPenaltyProcessor (deduplicates, sign-aware divide/multiply) - Integrate into Sequential, StaticShape, VLM, and Constrained engines - Only penalize generated tokens (not prompt) via generationStartOffset - Pipelined engine: hard fail with clear error (GPU path in follow-up) - CLI: --repetition-penalty and --repetition-penalty-window flags
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Extend MPSGraphCompositeSampler with an optional penalty stage (penaltyEnabled flag at init). When active, the compiled graph applies sign-aware penalty (divide positive logits, multiply negative) before topK. Refactor the monolithic graph-building init into composable static stage helpers (applyPenaltyStage, topKStage, temperatureStage, softmaxStage, minPStage, topPStage, maskAndNormalizeStage, multinomialStage, gatherTokenStage) that can be unit-tested independently. RepetitionPenaltyGPUState manages per-pipeline-depth rotating penalty buffers with dirty-tracking: recordToken() updates only CPU-side ring state, and buffer(forStep:) applies pending writes at encode time when the gate guarantees no in-flight GPU read on that slot. Inherent 2-token staleness from pipelineDepth=3 is acceptable for practical window sizes. Greedy + penalty on pipelined is rejected at entry (use sequential).
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Adds repetition penalty to existing sampler pipelines.
For sequential ones, provides immediate logits penalty
For pipelined engine, it lags by the pipeline depth - 1 (currently: 2)
Closes: #43
A follow up should provide a better interface for logits buffer manipulation (currently only contained sampling and repetition penalty, so duplication is acceptable)