A Full-System Simulation Framework for CXL-Based SSD Memory System (2501.02524v1)

Abstract: Compute eXpress Link (CXL) is a promising technology for memory disaggregation and expansion. Especially, CXL makes it more effectively for large-capacity storage devices such as Solid State Drive (SSD) to be deployed in the memory pool. However, CXL-based SSDs are still in early stages, necessitating the development of reliable simulation tools. In this paper, we propose CXL-SSD-Sim, the first open-source full-system simulator designed to simulate CXL-based SSD memory system. Constructed on the foundation of gem5 and SimpleSSD, CXL-SSD-Sim extends an high fidelity SSD memory expander model along with the corresponding device driver. In addition, CXL-SSD-Sim models a DRAM layer as a caching mechanism for the SSD, meticulously engineered to counteract latency issues inherent to CXL-based SSD memory access. Experiments are performed among five different memory devices with CXL-SSD-Sim in aspect of latency, bandwidth and real-world benchmark performance. These experiments serve to underscore the efficacy of our simulation tool in providing a comprehensive analysis of CXL-based SSD memory systems. The CXL-SSD-Sim simulator is available at https://github.com/WangYaohuii/CXL-SSD-Sim.

• The paper develops CXL-SSD-Sim, an open-source framework that models CXL-based SSD memory systems with detailed performance analysis.
• It integrates a DRAM caching layer to significantly reduce latency and enhance responsiveness in SSD memory systems.
• Experimental validation shows the simulator accurately measures latency and throughput across DRAM, persistent memory, and CXL-based SSD configurations.

Overview of "A Full-System Simulation Framework for CXL-Based SSD Memory System"

The paper "A Full-System Simulation Framework for CXL-Based SSD Memory System" introduces CXL-SSD-Sim, an open-source simulation framework designed to model and evaluate Compute Express Link (CXL)-based Solid State Drive (SSD) memory systems. In response to the demand for increased server memory capacity driven by applications such as LLMs and other data-intensive applications, CXL represents a technology capable of addressing the memory wall issue by facilitating memory disaggregation and expansion.

The paper emphasizes the early stages of CXL-based SSDs, highlighting the need for reliable simulation tools to investigate and optimize such systems. CXL-SSD-Sim is built on the foundations of gem5 and SimpleSSD, integrating high-fidelity SSD memory expander models and corresponding device drivers. Key design features of CXL-SSD-Sim include a DRAM caching layer, engineered to ameliorate the latency constraints inherent to SSDs when interfaced via CXL.

Key Contributions

• CXL-based SSD Memory Expander Model: The authors developed a comprehensive model of CXL-based SSD memory with a system-level simulation capability, enabling detailed performance analysis and optimization.
• DRAM Cache Integration: To counteract latency issues associated with SSD access, the design incorporates a DRAM cache layer that enhances system responsiveness and extends SSD endurance.
• Experimental Validation: The framework was used to conduct empirical assessments of different memory devices, including DRAM, persistent memory (PMEM), and CXL-SSDs, under various configurations. The results attested to the simulator's efficacy and accuracy as a research tool.

Experimental Findings

Two core experimental evaluations were conducted using CXL-SSD-Sim: latency and bandwidth testing, and application performance evaluations using key-value store scenarios.

1. Latency and Bandwidth: The paper demonstrated that CXL-SSD-Sim could emulate CXL-DRAM-like latency when a DRAM cache layer is enabled, showing bandwidth performance close to native CXL-DRAM. Without caching, SSDs exhibited significantly higher latency. However, with caching configurations such as LRU, the performance improved substantially due to reduced backend storage traffic and increased cache hit rates.
2. Application Workload Analysis: Using Viper, a key-value store benchmark, the authors assessed throughput for various operation types across storage device paradigms. CXL-SSD supplemented with a DRAM cache showed competitive performance compared to PMEM and highlighted the importance of caching techniques for enhancing SSD access efficiency. Strategies such as LRU cache replacement demonstrated superior utility in scenarios with high temporal locality.

Implications and Future Perspectives

The implications of this research are twofold: practical and theoretical. Practically, it provides an essential toolkit for exploring memory disaggregation benefits and optimizing SSD-based memory systems within the CXL protocol framework. This is particularly relevant as the industry moves towards heterogeneous, data-centric computing architectures and AI-driven workloads that necessitate large-scale memory solutions.

From a theoretical perspective, this work invites further exploration of memory system architectures that leverage CXL, encouraging the development of novel techniques to mitigate SSD latency in memory-pooled environments. The introduction of DRAM layers and various caching strategies offer insight into potential architectural enhancements that could be standardized in future CXL implementations.

In conclusion, CXL-SSD-Sim is an important contribution to the paper of memory expansion technologies, providing the community an accessible platform to test and refine emerging CXL-based memory solutions. As Compute Express Link continues to evolve, frameworks like CXL-SSD-Sim will be indispensable tools for both academic and industrial research endeavors, driving forward the capabilities of memory-intensive computational applications.