通过并行计算提升语言模型性能,显著降低内存与延迟开销。
Parallel Scaling Law for Language Models
- 对输入施加P个可学习变换,模型并行处理后动态融合输出。
- 相比参数量扩展,相同性能提升下内存增长仅1/22,延迟增加仅1/6。
- 可复用预训练模型,小规模微调即可实现并行化,适合资源受限场景。
普遍认为扩大语言模型需付出高昂的空间或时间成本,通过增加参数量(参数扩展)或输出长度(推理时扩展)。本文提出第三种更高效的扩展范式:在训练和推理阶段同时增加并行计算。具体地,对输入应用P个多样且可学习的变换,模型并行执行前向传播,并动态聚合P个输出。该方法称为并行扩展(ParScale),通过重用现有参数扩展并行计算能力,适用于任意模型结构、优化方法、数据或任务。我们理论推导出新的扩展规律,并通过大规模预训练验证:具有P个并行流的模型,其效果相当于参数量扩展至O(log P),但推理效率更高。例如,实现同等性能提升时,相比参数扩展,内存增长最多减少22倍,延迟增加减少6倍。此外,可通过少量令牌的后训练,将现成预训练模型转化为并行扩展版本,进一步降低训练成本。这一新扩展规律有望推动更强模型在低资源环境中的部署,并为计算在机器学习中的作用提供新视角。
原文摘要 · Abstract (English)
It is commonly believed that scaling language models should commit a significant space or time cost, by increasing the parameters (parameter scaling) or output tokens (inference-time scaling). We introduce the third and more inference-efficient scaling paradigm: increasing the model's parallel computation during both training and inference time. We apply $P$ diverse and learnable transformations to the input, execute forward passes of the model in parallel, and dynamically aggregate the $P$ outputs. This method, namely parallel scaling (ParScale), scales parallel computation by reusing existing parameters and can be applied to any model structure, optimization procedure, data, or task. We theoretically propose a new scaling law and validate it through large-scale pre-training, which shows that a model with $P$ parallel streams is similar to scaling the parameters by $O(\log P)$ while showing superior inference efficiency. For example, ParScale can use up to 22$\times$ less memory increase and 6$\times$ less latency increase compared to parameter scaling that achieves the same performance improvement. It can also recycle an off-the-shelf pre-trained model into a parallelly scaled one by post-training on a small amount of tokens, further reducing the training budget. The new scaling law we discovered potentially facilitates the deployment of more powerful models in low-resource scenarios, and provides an alternative perspective for the role of computation in machine learning.
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