Bus Exchange Switch for Multi-Socket Server PCIe Lane Allocation
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Solution Overview
Problem
In two-socket servers, network or storage I/O devices connected to one processor experience slower access by the second processor due to latency and flow control issues, and there is a scarcity of PCIe lanes to service access controllers and network interfaces, forcing system designers to make unattractive choices that compromise the benefits of multi-socket systems.
Innovation Solution
An information handling system with a bus exchange switch that creates different electrical paths between processor sockets and resources based on the population status of the second processor socket, ensuring efficient access to network interfaces and management controllers by either bypassing the second socket when unpopulated or enabling inter-socket communication when populated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PCIe lanes are reserved for processor-to-processor handshaking protocols in a two-socket system, then inter-socket communication is enabled, but the number of available lanes for servicing access controllers and network interfaces is reduced
Solution Approach 1:
The system dynamically configures PCIe lane assignments based on whether the second processor socket is populated. When socket 2 is unpopulated, all PCIe lanes are allocated to socket 1 for servicing I/O devices. When socket 2 is populated, the system automatically reserves certain lanes for inter-socket communication while maintaining adequate lanes for I/O devices, eliminating the need for manual configuration choices.
Solution Approach 2:
The PCIe switch fabric provides multi-functional capability by serving both I/O device connectivity and inter-socket communication functions through the same physical infrastructure. The same PCIe lanes can be dynamically assigned to different purposes based on system configuration, allowing the system to handle both access controller/network interface traffic and processor-to-processor handshaking protocols without requiring separate dedicated lanes.
2Reliability
If the network interface is connected to the second processor, then the first processor can access it, but the system loses the advantage of having more I/O directly connected to each processor in a multi-socket system
Solution Approach 1:
The PCIe switch fabric acts as an intermediary that enables the first processor to access network interfaces and access controllers regardless of which processor socket they are physically connected to. This mediator provides transparent routing, allowing socket 1 to access I/O devices connected to socket 2 without requiring the I/O devices to be directly connected to socket 1, thus preserving the scalability benefits of multi-socket configurations.
Solution Approach 2:
The system segments I/O device assignments by processor socket, allowing each processor to have its own dedicated I/O connections while still enabling cross-socket access through the PCIe switch fabric. This segmentation maintains the advantage of having more I/O directly connected to each processor in multi-socket systems while ensuring all processors can access all I/O resources when needed.
3Ease of manufacture
If a x16 PCIe port is bifurcated to connect the network interface, then the network interface can be connected, but this minimizes the advantage of multi-socket systems which provides more I/O directly connected to the processor
Solution Approach 1:
The system dynamically determines the optimal connection configuration based on socket population status. When socket 2 is unpopulated, the system can allocate PCIe lanes more flexibly to serve I/O devices without reserving lanes for inter-socket communication. This dynamic allocation eliminates the need for fixed bifurcation configurations and preserves the full I/O connectivity advantages of multi-socket systems.
Data Source
AI summary
In accordance with embodiments of the present disclosure, an information handling system may include two processor sockets comprising a first processor socket and a second processor socket, a first information handling resource communicatively coupled to the first processor socket, second information handling resource, and a bus exchange switch communicatively coupled to the first processor socket, the second processor socket, and the second information handling resource such that: if the second processor socket is unpopulated, the bus exchange switch creates a first electrically conductive path between the first processor socket and the second information handling resource, and if the second processor socket is populated, the bus exchange switch creates a second electrically conductive path between the first processor socket and the second processor socket and creates a third electrically conductive path between the second processor socket and the second information handling resource.