OpenCXD: An Open Real-Device-Guided Hybrid Evaluation Framework for CXL-SSDs

TL;DR

OpenCXD is a hybrid evaluation framework that combines real hardware and simulation to accurately assess CXL-SSD performance, capturing low-level device behaviors often missed by pure simulations.

Contribution

It introduces a real-device-guided approach that integrates a CXL.mem simulator with actual hardware, enabling more faithful performance evaluation of CXL-SSDs.

Findings

Enables in-situ firmware execution for realistic testing

Captures device-level phenomena unobservable in pure simulation

Provides insights for firmware optimization in CXL-SSDs

Abstract

The advent of Compute Express Link (CXL) enables SSDs to participate in the memory hierarchy as large-capacity, byte-addressable memory devices. These CXL-enabled SSDs (CXL-SSDs) offer a promising new tier between DRAM and traditional storage, combining NAND flash density with memory-like access semantics. However, evaluating the performance of CXL-SSDs remains difficult due to the lack of hardware that natively supports the CXL.mem protocol on SSDs. As a result, most prior work relies on hybrid simulators combining CPU models augmented with CXL.mem semantics and SSD simulators that approximate internal flash behaviors. While effective for early-stage exploration, this approach cannot faithfully model firmware-level interactions and low-level storage dynamics critical to CXL-SSD performance. In this paper, we present OpenCXD, a real-device-guided hybrid evaluation framework that bridges the gap between simulation and hardware. OpenCXD integrates a cycle-accurate CXL.mem simulator on the host side with a physical OpenSSD platform running real firmware. This enables in-situ firmware execution triggered by simulated memory requests. Through these contributions, OpenCXD reflects device-level phenomena unobservable in simulation-only setups, providing critical insights for future firmware design tailored to CXL-SSDs.