Ultra Path Interconnect

Ultra Path Interconnect
Name	Ultra Path Interconnect
Developer	Intel Corporation
Type	Point-to-point interconnect
Predecessor	Intel QuickPath Interconnect
Successor	Compute Express Link

Ultra Path Interconnect. It is a high-speed, point-to-point processor interconnect architecture developed by Intel Corporation for its Xeon server platforms. Designed as a successor to the Intel QuickPath Interconnect, it aimed to significantly boost data transfer rates and reduce latency in multi-socket systems. The technology was pivotal for high-performance computing and enterprise server workloads, facilitating coherent memory access across complex NUMA architectures.

Overview

The primary function was to enable efficient communication between CPUs and between processors and other critical system components like I/O hubs. It served as the backbone for scalable systems in data centers running applications from VMware and managing large databases like Oracle Database. This interconnect was integral to platforms competing with offerings from Advanced Micro Devices and IBM, particularly in the market for supercomputer and cloud computing infrastructure. Its design emphasized low latency and high bandwidth to meet the demands of evolving computational models.

Technical Specifications

Operating at significantly higher data rates than its predecessor, it utilized differential signaling and advanced clocking techniques. The physical layer was based on a serial communication protocol with multiple lanes, each capable of multi-gigabit transfer speeds. It supported cache coherency protocols essential for maintaining data integrity across sockets in a SMP system. Error correction was handled through robust CRC and link-level retry mechanisms, ensuring reliability for critical enterprise applications.

Architecture and Design

The architecture employed a layered model, comprising a physical layer, link layer, and protocol layer. It used a packet-switched network-on-a-chip approach for routing transactions, which improved scalability. The design featured a distributed directory for cache coherency, an evolution of the MESI protocol used in earlier Intel interconnects. Routing was managed by on-die controllers that minimized hops between nodes in a mesh or ring topology, optimizing path selection for reduced latency.

Performance and Applications

Performance benchmarks demonstrated substantial improvements in bandwidth and latency-sensitive workloads, benefiting fields like computational fluid dynamics and financial modeling. It was extensively used in high-performance computing systems, such as those on the TOP500 list, and for large-scale virtualization environments. Major cloud providers like Amazon Web Services and Microsoft Azure utilized servers built on this technology for their instance offerings. Its performance was crucial for accelerating applications in artificial intelligence and big data analytics frameworks like Apache Spark.

Comparison with Other Interconnects

When compared to its direct predecessor, Intel QuickPath Interconnect, it offered markedly higher data rates and improved power efficiency. Against contemporary alternatives like HyperTransport from Advanced Micro Devices or InfiniBand used in cluster networks, it was optimized for intra-system coherence rather than external expansion. Unlike open-standard interconnects like PCI Express, it was a proprietary technology focused solely on processor-to-processor communication within a single platform. Its design philosophy differed from emerging coherent fabrics like Compute Express Link, which aimed for a more open, heterogeneous ecosystem.

Development and History

Development was initiated by Intel engineers to address bottlenecks in multi-socket Xeon servers, with key research stemming from work at Intel Labs. It was first introduced commercially with the Skylake-SP microarchitecture generation of Xeon processors. The project involved collaborations with major OEMs like Hewlett Packard Enterprise and Dell Technologies for platform integration. Its evolution was influenced by the competitive landscape, including the reintroduction of EPYC processors by AMD, and was eventually superseded by industry-wide efforts toward standards like Compute Express Link.

Category:Computer hardware Category:Intel Category:Computer buses