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Efficient Inference for Large Language Model-based Generative Recommendation
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Proposes AtSpeed, an alignment framework for speculative decoding in LLM-based generative recommendation under N-to-K (top-K beam) verification, with a strict-verification objective (AtSpeed-S) and a relaxed sampling verification with TVD alignment (AtSpeed-R), achieving ~2x walltime speedup on Amazon Beauty and Games.
Problem
Speculative decoding for LLM-based generative recommendation is hard because beam search must return top-K distinct item sequences, so every step requires the draft model to cover all top-K sequences of the target LLM (N-to-K verification), limiting acceptance and speedup.
Approach
Align the draft model to the target LLM's top-K sequence distribution: under strict top-K verification, minimize a reverse-KL alignment loss with a density regularizer over constrained top-K tokens (AtSpeed-S); under a relaxed sampling verification that accepts high-probability non-top-K drafts with probability p/q, minimize TVD on top-K sequences (AtSpeed-R), with tree-based attention for efficie
Key results
- AtSpeed-S under strict top-K verification achieves average walltime speedup of 1.97x on Beauty and 1.83x on Games with identical top-K results.
- AtSpeed-R under relaxed sampling verification reaches average speedup of 2.11x on Beauty and 2.05x on Games.
- Relaxed sampling verification generally yields higher speedup than strict top-K verification across methods, with only limited Recall@5/NDCG@5 drops.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use relaxed sampling verification instead of strict top-K verification | AtSpeed-R · Beauty | Avg WS: 1.76 -> 2.11 | Helped |
| use relaxed sampling verification instead of strict top-K verification | AtSpeed-R · Games | Avg WS: 1.74 -> 2.05 | Helped |
| add density regularization (ablation) | AtSpeed-S · Beauty | acceptance rate | Helped |
| use target top-K sequences instead of only the top-1 sequence for alignment (ablation) | AtSpeed-R · Beauty | acceptance rate | Helped |
| add constrained alignment (ablation) | AtSpeed-S and AtSpeed-R · Beauty | speedup | Helped |
| add tree-based attention (ablation) | AtSpeed-S and AtSpeed-R · Beauty | speedup | Helped |
| increase draft beam size from 20 to 60 | AtSpeed-S and AtSpeed-R · Beauty | walltime speedup | Helped |
| increase alignment strength from 0 | AtSpeed-S · Beauty | acceptance rate | Helped |
| overemphasize alignment loss | AtSpeed-S · Beauty | acceptance rate | Hurt |
Surprising findings
- Logit-level KD methods (WordKD, TVDKD) often perform comparable to or worse than plain SFT for the draft model.
- Using only the target LLM's top-1 sequence for AtSpeed-R lowers acceptance, since it lacks diversity.
Limitations
- Only evaluated on LC-Rec with LLaMA-7B target and LLaMA-68M draft; generalization to other generative recommenders is not shown.
- Relaxed verification trades a small accuracy drop for speed; the equivalence relies on a with-replacement sampling approximation.
- Draft model is an LLM-sized small model, so drafting overhead remains.
Experimental setup
Datasets: Amazon Beauty Amazon Games MovieLens-1M Goodreads
Benchmarks: Amazon Beauty Amazon Games MovieLens-1M Goodreads
Metrics: walltime speedup (WS@K) accept steps (AS@K) Recall@K NDCG@K
Baselines: DARE SFT WordKD TVDKD SeqKD
Builds on: speculative decoding DistillSpec LC-Rec SeqKD TVDKD
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