OCEAN: Open-source CXL Emulation at Hyperscale Architecture and Networking

Compute Express Link (CXL)~3.0 introduces powerful memory pooling and promises to transform datacenter architectures. However, the lack of available CXL~3.0 hardware and the complexity of multi-host configurations pose significant challenges to the community. This paper presents OCEAN, a comprehensive emulation framework that enables full CXL~3.0 functionality, including multi-host memory sharing and pooling support. OCEAN provides emulation of CXL~3.0 features—such as fabric management, dynamic memory allocation, and coherent memory sharing across multiple hosts—in advance of real hardware availability. OCEAN uses QEMU virtualization and custom kernel modules to create a realistic CXL~3.0 environment that supports up to 16 hosts sharing a common memory pool, including CXL~3.0 features such as Global Fabric Attached Memory (GFAM), Multi-Headed Single Logical Device (MH-SLD), and dynamic capacity devices (for hot-pluggable memory). An evaluation of OCEAN shows that it achieves performance within about 3x of projected native CXL~3.0 speeds having complete compatibility with existing CXL software stacks.