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MagicDec: Breaking the Latency-Throughput Tradeoff for Long Context Generation with Speculative Decoding

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arxiv 2408.11049 v5 pith:U6XM5DAD submitted 2024-08-20 cs.CL

classification cs.CL
keywords batchspeedupthroughputdecodinghighlatencylonglong-context
verification ladder T0 review T1 audit T2 compute T3 formal
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Large Language Models (LLMs) have become more prevalent in long-context applications such as interactive chatbots, document analysis, and agent workflows, but it is challenging to serve long-context requests with low latency and high throughput. Speculative decoding (SD) is a widely used technique to reduce latency losslessly, but the conventional wisdom suggests that its efficacy is limited to small batch sizes. In MagicDec, we show that surprisingly SD can achieve speedup even for a high throughput inference regime for moderate to long sequences. More interestingly, an intelligent drafting strategy can achieve better speedup with increasing batch size based on our rigorous analysis. MagicDec first identifies the bottleneck shifts with increasing batch size and sequence length, and uses these insights to deploy SD more effectively for high throughput inference. We leverage draft model with sparse KV cache to address the KV bottleneck, which scales with both sequence length and batch size. Additionally, we propose a theoretical model to select the optimal drafting strategy for maximum speedup. Our work highlights the broad applicability of speculative decoding in long-context serving, as it can enhance throughput and reduce latency without compromising accuracy. For moderate to long sequences, we demonstrate up to 2.51x speedup for Llama3.1-8B when serving batch sizes ranging from 32 to 256 on various types of hardware and tasks.

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Cited by 8 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. A Sparse Glimpse of the Whole: Train-Free Self-Speculative Decoding

    cs.CL 2026-07 conditional novelty 6.0 of 10

    A training-free self-speculative decoding system with a recallable sparse KV cache and entropy-guided adaptive speculation achieves up to 2.79× speedup while preserving the target distribution.

  2. Revisiting Lossy Verification in Speculative Decoding: Mechanisms, Trade-offs, and Failure Modes

    cs.CL 2026-07 conditional novelty 6.0 of 10

    Lossy speculative-decoding verification splits into truncation-based and collaborative methods; truncation-based methods underperform their matched baselines, and capping draft overshoot preserves quality.

  3. Windowed-MTP: Removing the Full-Context Draft-KV Tax at Million-Token Context

    cs.LG 2026-07 conditional novelty 6.0 of 10

    Restricting the built-in draft head's attention to a 4K sink-plus-recent window cuts long-context speculative-decoding step cost by 28-44% without changing the target model's output distribution.

  4. Kinetics: Rethinking Test-Time Scaling Laws

    cs.LG 2025-06 conditional novelty 6.0 of 10

    A memory-aware test-time scaling law shows small models are overestimated and sparse attention is needed for efficient scaling.

  5. Rectified Sparse Attention

    cs.CL 2025-06 conditional novelty 6.0 of 10

    ReSA keeps sparse decoding accurate by refreshing the KV cache with dense attention every f tokens, achieving near-lossless quality with a large speedup.

  6. POSS: Position Specialist Generates Better Draft for Speculative Decoding

    cs.CL 2025-06 conditional novelty 6.0 of 10

    Using position-specialized draft layers instead of one single draft model improves later-token acceptance in speculative decoding, yielding modest speedups on Llama-3-8B and Llama-2-13B.

  7. Speculative Decoding Reimagined for Multimodal Large Language Models

    cs.CV 2025-05 conditional novelty 6.0 of 10

    MSD decouples text and visual tokens in the draft model and trains it first on text, then on a gradually increasing mix of visual data, yielding roughly 2x lossless speedups on LLaVA benchmarks.

  8. Efficient Speculative Decoding for Llama at Scale: Challenges and Solutions

    cs.CL 2025-08 conditional novelty 5.0 of 10

    Meta reports EAGLE-based speculative decoding optimizations for Llama models, achieving state-of-the-art latency (about 4 ms/token for Llama4 Maverick) and 1.4-2.0x speedups for large batches.

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