vLLM: Revolutionizing LLM Serving with PagedAttention

Published on 4/30/2024

Hey there! Today, we're diving deep into something that's been creating waves in the AI community – vLLM. If you're into AI and large language models (LLMs), you're going to want to hear about this. vLLM is not just another tool; it's a game-changer in how we serve and utilize LLMs, making them faster, more efficient, and accessible to a wider range of projects and teams. Buckle up, because we're about to explore what makes vLLM so special, and why it might just be the breakthrough we've been waiting for.

In the world of artificial intelligence, the promise of large language models (LLMs) has been nothing short of revolutionary. These models have the potential to transform industries, offering new ways to interact with technology and process information. However, the reality of serving these models has been fraught with challenges. They require substantial computational resources, and despite the availability of powerful hardware, serving LLMs can be surprisingly slow and expensive. That's where vLLM comes in, a beacon of innovation in the often turbulent seas of AI technology.

vLLM: Easy, Fast, and Cheap LLM Serving with PagedAttention

Introduced on June 20, 2023, by a team from UC Berkeley, vLLM stands as a testament to what collaborative innovation can achieve. Developed by Woosuk Kwon, Zhuohan Li, Siyuan Zhuang, Ying Sheng, Lianmin Zheng, Cody Yu, Joey Gonzalez, Hao Zhang, and Ion Stoica, vLLM addresses the core issues facing LLM serving head-on. By leveraging a novel attention algorithm called PagedAttention, vLLM significantly outperforms existing solutions in terms of throughput and efficiency.

Key Highlights:

• GitHub | Documentation | Paper: vLLM (opens in a new tab) is an open-source treasure trove for those looking to dive into the technicalities or simply start utilizing it for their own LLM serving needs (opens in a new tab).
• Unmatched Performance: In benchmarks, vLLM delivers up to 24x higher throughput compared to popular libraries like HuggingFace Transformers, all without requiring any changes to the model architecture.

The Secret Behind Its Success: PagedAttention

• At its core, PagedAttention addresses the memory bottleneck in LLM serving. By managing attention keys and values more effectively, it allows for high throughput and efficient memory usage.
• Flexibility and Efficiency: Inspired by virtual memory systems in operating systems, PagedAttention stores keys and values in non-contiguous memory blocks, allowing for dynamic and efficient memory management.
• Optimized Memory Usage: This method drastically reduces memory waste and enables higher GPU utilization, translating into better performance.

Practical Applications and Impact

• Real-World Deployment: vLLM has been deployed in platforms like Chatbot Arena and Vicuna Demo, demonstrating its effectiveness in serving millions of users.
• Cost Efficiency: By improving throughput and reducing GPU requirements, vLLM enables small teams to serve LLMs affordably, democratizing access to cutting-edge AI technologies.

Getting Started with vLLM

For those eager to get their hands dirty, getting started with vLLM is as straightforward as running a single command to install it from GitHub. Whether you're looking to perform offline inference or set up an online serving system, vLLM offers flexibility and ease of use.

• Installation: Simple and user-friendly, requiring just a single command to get up and running.
• Usage Scenarios: Supports a variety of use cases, from batched inference on datasets to running an OpenAI API-compatible server for online serving.

vLLM in Action: A Step-by-Step Guide

To give you a taste of what working with vLLM looks like, here's a quick rundown:

1. Offline Batched Inference: Learn how to use vLLM for high-throughput text generation from a list of prompts.
2. Building an API Server: Step through the process of setting up an API server for LLM serving, compatible with the OpenAI API.
3. Advanced Features: Explore the capabilities of vLLM, including parallel sampling and beam search, to see how it handles complex sampling algorithms with ease.

as it paves the way for more accessible, efficient, and scalable LLM serving. Whether you're a researcher, a developer, or just an AI enthusiast, vLLM offers an opportunity to push the boundaries of what's possible with large language models. Now, let's dive into the technical details and see vLLM in action.

Diving Deeper into vLLM

vLLM stands out not only for its impressive performance but also for its ease of use. It provides a seamless integration with existing tools and workflows, making it a versatile choice for a variety of LLM serving needs.

Core Features of vLLM

vLLM brings to the table a suite of features that address many of the challenges associated with LLM serving:

• State-of-the-art serving throughput: Leveraging optimized CUDA kernels and the innovative PagedAttention algorithm, vLLM achieves unparalleled serving speeds.
• Efficient memory management: Through PagedAttention, vLLM efficiently manages attention key and value memory, drastically reducing the memory footprint of LLM inference.
• Continuous batching: vLLM can continuously batch incoming requests, maximizing hardware utilization and throughput.
• Optimized CUDA kernels: The use of custom CUDA kernels further enhances performance, ensuring that vLLM runs as efficiently as possible.

Getting Started with vLLM and LangChain

Integrating vLLM into your projects is straightforward, thanks to its compatibility with popular Python packages. Here's a quick start guide:

1. Installation: Ensure you have the vllm python package installed. You can install it using pip:

   %pip install --upgrade --quiet vllm -q

2. Basic Usage: Begin by importing VLLM from the langchain_community.llms package and initializing it with your desired model. Here's an example:

   from langchain_community.llms import VLLM
    
   llm = VLLM(
       model="mosaicml/mpt-7b",
       trust_remote_code=True,  # mandatory for hf models
       max_new_tokens=128,
       top_k=10,
       top_p=0.95,
       temperature=0.8,
   )
    
   print(llm.invoke("What is the capital of France ?"))

   This simple script demonstrates how to perform inference, returning "Paris" as the capital of France.

Enhancing Inference with LLMChain

For more complex inference tasks, vLLM can be integrated into an LLMChain, allowing for sophisticated prompt engineering and processing:

from langchain.chains import LLMChain
from langchain.prompts import PromptTemplate
 
template = """Question: {question}
 
Answer: Let's think step by step."""
prompt = PromptTemplate.from_template(template)
 
llm_chain = LLMChain(prompt=prompt, llm=llm)
 
question = "Who was the US president in the year the first Pokemon game was released?"
 
print(llm_chain.invoke(question))

This approach enables step-by-step reasoning, providing detailed answers to complex questions.

Distributed Inference and Quantization

vLLM supports advanced features like distributed inference and quantization, making it suitable for high-demand environments:

• Distributed Inference: To leverage multiple GPUs, simply set the tensor_parallel_size argument when initializing VLLM.
• Quantization: vLLM also supports AWQ quantization, which can significantly reduce the model's memory footprint without sacrificing performance.

OpenAI-Compatible Server

One of the most powerful features of vLLM is its ability to mimic the OpenAI API protocol, making it a drop-in replacement for applications currently using the OpenAI API. This capability opens up a world of possibilities for deploying efficient, scalable LLM solutions.

Conclusion: The Future of LLM Serving with vLLM

vLLM represents a significant leap forward in LLM serving technology. With its combination of high throughput, efficient memory management, and ease of use, vLLM is well-positioned to become a key player in the AI landscape. Whether you're looking to enhance existing applications or explore new possibilities with LLMs, vLLM offers the tools and performance to make your projects a success. As the community continues to explore and expand upon vLLM's capabilities, we can expect even more innovative applications and improvements in the future.