vLLM Metal Plugin

High-performance LLM inference on Apple Silicon using MLX and vLLM

vLLM Metal is a plugin that enables vLLM to run on Apple Silicon Macs using MLX as the primary compute backend. It unifies MLX and PyTorch under a single lowering path.

Features

• MLX-accelerated inference: faster than PyTorch MPS on Apple Silicon
• Unified memory: True zero-copy operations leveraging Apple Silicon's unified memory architecture
• vLLM compatibility: Full integration with vLLM's engine, scheduler, and OpenAI-compatible API
• Paged attention: Efficient KV cache management for long sequences
• GQA support: Grouped-Query Attention for efficient inference

Requirements

• macOS on Apple Silicon

Installation

curl -fsSL https://raw.githubusercontent.com/vllm-project/vllm-metal/main/install.sh | bash

Architecture

┌─────────────────────────────────────────────────────────────┐
│                          vLLM Core                          │
│          Engine, Scheduler, API Server, Tokenizers          │
└─────────────────────────────────────────────────────────────┘
                               │
                               ▼
┌─────────────────────────────────────────────────────────────┐
│                   vllm_metal Plugin Layer                   │
│ ┌─────────────────┐ ┌────────────────┐ ┌──────────────────┐ │
│ │ MetalPlatform   │ │ MetalWorker    │ │ MetalModelRunner │ │
│ │ (Platform)      │ │ (Worker)       │ │ (ModelRunner)    │ │
│ └─────────────────┘ └────────────────┘ └──────────────────┘ │
└─────────────────────────────────────────────────────────────┘
                               │
                               ▼
┌─────────────────────────────────────────────────────────────┐
│                   Unified Compute Backend                   │
│ ┌───────────────────────────┐ ┌───────────────────────────┐ │
│ │   MLX Backend             │ │   PyTorch Backend         │ │
│ │   (Primary)               │ │   (Model Loading/Interop) │ │
│ │                           │ │                           │ │
│ │ • SDPA Attention          │ │ • HuggingFace Loading     │ │
│ │ • RMSNorm                 │ │ • Weight Conversion       │ │
│ │ • RoPE                    │ │ • Tensor Bridge           │ │
│ │ • Cache Ops               │ │                           │ │
│ └───────────────────────────┘ └───────────────────────────┘ │
└─────────────────────────────────────────────────────────────┘
                               │
                               ▼
┌─────────────────────────────────────────────────────────────┐
│                       Metal GPU Layer                       │
│          Apple Silicon Unified Memory Architecture          │
└─────────────────────────────────────────────────────────────┘

Configuration

Environment variables for customization:

Variable	Default	Description
VLLM_METAL_MEMORY_FRACTION	auto	auto allocates just enough memory plus a minimal KV cache, or 0.? for fraction of memory
VLLM_METAL_USE_MLX	1	Use MLX for compute (1=yes, 0=no)
VLLM_MLX_DEVICE	gpu	MLX device (gpu or cpu)
VLLM_METAL_BLOCK_SIZE	16	KV cache block size
VLLM_METAL_DEBUG	0	Enable debug logging