On Speculative Decoding for Multimodal Large Language Models

本文是LLM系列文章,针对《On Speculative Decoding for Multimodal Large Language Models》的翻译。

多模态大型语言模型的推测解码

摘要

多模态大型语言模型(MLLM)的推理速度很慢,因为它们的大型语言模型主干受到内存带宽瓶颈的影响,并自动回归生成token。本文探讨了推测解码在提高MLLM推理效率方面的应用,特别是LLaVA 7B模型。我们证明,仅使用语言的模型可以作为LLaVA 7B推测解码的良好草稿模型,绕过了草稿模型对图像标记及其相关处理组件的需求。我们在三个不同任务上的实验表明,使用我们从头开始训练的115M参数语言模型,推测解码可以实现高达2.37倍的内存限制加速。此外,我们引入了一个紧凑的LLaVA草稿模型,其中包含一个图像适配器,该模型在图像字幕方面显示了边际性能提升,同时在其他任务中保持了可比的结果。

1 引言

2 背景

3 SPD用于MLLMs

4 实验

5 结论

在本文中,我们首次尝试在使用多模态大型语言模型时使用推测解码来加速推理,特别是在图像文本域。我们表明,使用纯文本草稿模型比使

### Speculative Decoding in LMStudio Implementation and Usage In the context of large language models (LLMs), speculative decoding is an optimization technique aimed at improving inference efficiency by predicting future tokens before they are fully computed. This approach leverages parallelism within GPUs or TPUs to reduce latency during text generation tasks. #### Key Concepts Behind Speculative Decoding To understand how speculative decoding works, it's important to recognize that traditional autoregressive models generate one token at a time based on previous tokens. However, this sequential nature can lead to inefficiencies as each new prediction must wait for preceding computations to complete. By contrast, speculative decoding attempts to predict multiple potential next tokens simultaneously while maintaining reasonable accuracy[^1]. #### Memory Optimization Techniques Training multi-token predictors poses significant challenges regarding GPU memory utilization due to the disparity between vocabulary size \( V \) and embedding dimensions \( d \). Naive implementations materialize all logits along with their gradients, leading to substantial memory consumption. To mitigate these issues: - The architecture suggests carefully orchestrating forward and backward operations. - After sharing the trunk computation across independent output heads, individual forward passes followed immediately by corresponding backpropagation steps occur sequentially. - Logits generated from each head get discarded once no longer needed, retaining only essential gradient information related to the main model parameters[^2]. This strategy effectively reduces peak GPU memory usage without introducing additional runtime overheads. #### Practical Application Within LMStudio Within LMStudio, implementing speculative decoding involves several considerations: ```python def speculative_decode(model, input_sequence, max_length=50): predictions = [] for i in range(max_length): # Perform standard forward pass up until last known token hidden_state = model.forward(input_sequence) # Generate top-k candidates using current state candidate_tokens = model.top_k_sampling(hidden_state, k=5) # Select most probable continuation path among candidates best_token_id = select_best_continuation(candidate_tokens) # Append chosen token ID to sequence for subsequent iterations input_sequence.append(best_token_id) predictions.append(best_token_id) # Early stopping condition when end-of-sequence detected if check_end_of_sequence(best_token_id): break return predictions ``` The provided code snippet demonstrates a simplified version of speculative decoding where after computing intermediate states, multiple possible continuations are evaluated probabilistically rather than waiting for deterministic outcomes step-by-step.
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