Intel® Flat Memory Mode on Intel® Xeon® 6 Processors

Introduction
Intel® Flat Memory Mode is a memory configuration feature designed for Intel Xeon 6 Processors to enhance system performance and reduce the total cost of ownership (TCO). This feature combines native DRAM (Near Memory) and CXL-attached DDR memory (Far Memory) to provide a single, unified memory region.

Key Features
The key features of Intel Flat Memory Mode include cost efficiency, memory management, and performance optimization. It enables the use of lower-cost memory, such as DDR4, alongside DDR5, and allows for the reuse of DDR4 memory from retired systems. The feature treats native DRAM as a cache for CXL-attached memory, keeping frequently accessed data in DRAM for optimal performance and storing less frequently accessed data in CXL memory.

Performance and Use Cases
Intel Flat Memory Mode maintains a 1:1 ratio between Near Memory (DRAM) and Far Memory (CXL-attached memory) for high performance. It provides near-native DRAM performance for workloads with good data locality, making it suitable for virtual machines (VMs), web and business applications, key-value stores, and in-memory databases.

Compatibility and Advantages
The feature is compatible with Intel Xeon 6 CPUs with P-cores (Granite Rapids) that support DDR4 and DDR5, and Intel Xeon 6 CPUs with E-cores (Sierra Forest) that support DDR5 only.

Intel Flat Memory Mode offers advantages over legacy 2LM (Two-Level Memory) by exposing the total memory capacity to the system, eliminating wasted capacity and improving performance consistency.

Relationship with CXL
While Intel Flat Memory Mode and CXL are distinct technologies, they complement each other in enhancing memory capacity, performance, and flexibility in modern computing environments. CXL can be used to connect additional memory resources, further enhancing the overall memory capacity and flexibility.

Unlike inclusive caching, there is no data replication in this mode, which means the data either exists in NM or FM. Hot data is moved to NM for faster performance.

This mode allows the use of lower-cost memory, improving TCO, and does not require any OS or application changes for managing memory tiers. Both the DDR and CXL memory are exposed to the system as a combined physical memory.

Key Features of CXL

• High-Speed Interconnect: Provides low-latency, high-bandwidth communication between CPUs and other devices.
• Memory Expansion: Supports memory pooling and sharing, allowing for more flexible and efficient use of memory resources across different components.
• Coherent Memory Access: Ensures data consistency and coherence between the CPU and connected devices, enabling more efficient data processing and sharing.
• Scalability: Designed to scale with future advancements in processor and memory technologies.
• Relationship Between Intel® Flat Memory Mode and CXL: While Intel® Flat Memory Mode and CXL are distinct technologies, they are related in the context of enhancing memory capacity, performance, and flexibility in modern computing environments.
• Memory Expansion: CXL can be used to connect additional memory resources, such as CXL-attached memory modules, to a system. This can complement the memory capacity provided by Intel® Flat Memory Mode, further enhancing the overall memory capacity and flexibility.
• Efficient Resource Utilization: Both technologies aim to improve the efficiency of memory usage in data centers and enterprise environments. Intel® Flat Memory Mode optimizes local memory usage, while CXL enables efficient sharing and pooling of memory resources across multiple components.

In summary, Intel® Flat Memory Mode and CXL are complementary technologies that together can provide significant benefits in terms of memory capacity, performance, and flexibility, addressing the growing demands of modern computing workloads.

Compatibility of CXL memory for Intel® Flat Memory Mode

• Intel Xeon 6 CPU (codenamed Granite Rapids-SP/AP): DDR4 & DDR5 
• Intel Xeon 6 CPU (codenamed Sierra Forest-SP/AP) and Future Intel Xeon CPU (codenamed Clearwater Forest-SP/AP): DDR5 only

For more information, visit Compute Express Link* (CXL*) Supplemental Validation Guide for Birch Stream (CNDA Required).