HPCwire: Remote Direct Memory Access Networking for HPC: Comparative Review of 10GbE iWARP and InfiniBand

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February 24, 2010

Remote Direct Memory Access Networking for HPC: Comparative Review of 10GbE iWARP and InfiniBand

by Saqib Jang, Margalla Communications

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The Rise of HPC Cluster Computing

While the HPC market is expected to experience a revenue dip in 2009, growth is expected to resume in 2010 and remain a bright spot in the overall IT market. The most important feature of the HPC growth trend is that it will continue to be fueled primarily by purchases of Linux cluster systems priced under $250,000. Cluster computing systems, separate compute nodes built from standard component technologies have caused disruptive changes in the HPC market.

As the component technologies of cluster systems have improved and buyers have become more confident running cluster systems, they have inevitably redirected capital once earmarked for large custom systems to larger cluster systems. These much larger clusters, often with thousands of processors, present opportunities for huge performance gains through improved parallel performance resulting in an overall higher order of magnitude return-on-investment (ROI). While algorithm and application tuning is often required to obtain these benefits, so often are cost, bandwidth, message rate, and latency of cluster interconnects.

One consequence of the range of requirements for cluster networking is that the leading interconnects in HPC are Gigabit Ethernet (which is based on Ethernet networking standard) and InfiniBand (delivering upwards of 10X performance vs. GbE). Both show significant deployment in HPC. The latest TOP500 list of HPC systems has 259 Gigabit Ethernet-based deployments compared to 181 InfiniBand-connected systems. The deployment of 10 Gigabit Ethernet (10GbE) cluster networking is emerging at this point. The price of this interconnect has been falling as the volume of its shipments grow. This growth is based on a combination of its 10X performance over GbE along with the ease of deployment due to its Ethernet heritage positions it for a bright future as a cluster interconnect.

As cluster systems have grown, so has the total amount of data in play in the average parallel HPC application. This has significant implications for HPC storage systems. Storage systems need to have the best possible bandwidth and latency characteristics. HPC storage systems have themselves become increasingly clustered and parallel as well as network-attached and accessible from all nodes on the cluster through the interconnect. In this context, the demand for interconnect solutions that supports a converged storage and cluster interconnect fabric is expected to grow significantly.

10GbE iWARP Overview and Value Proposition

For years, Ethernet has been the de facto standard LAN for connecting users to each other and to network resources. Ethernet sales volumes make it unquestionably the most cost-effective datacenter fabric to deploy and maintain. The latest generation of Ethernet, 10 Gigabit Ethernet (10GbE), offers a 10 Gbps data rate, which simplifies growth for existing data networking applications while removing the bandwidth barriers to deployment for highest-performance HPC clustering and storage networking.

10GbE end-to-end performance now compares very favorably with that of more specialized datacenter interconnects, which eliminates performance as a drawback to the adoption of an Ethernet unified data center fabric.
Off-loading cluster and storage protocol processing from the central CPU to intelligent 10GbE NIC can also improve the power efficiency of end stations because off-load ASIC processors are generally considerably more power-efficient in executing protocol workloads.
The value of implementing TCP/IP protocol processing in silicon at 10 Gbps data rates is clear. Effectively, such approaches have the potential of reducing the relative bandwidth and latency overhead effect of TCP/IP protocol processing to zero.

Achieving 10GbE performance for latency-sensitive HPC communications has required solving Ethernet's long-standing overhead problems; problems that, in slower Ethernet generations, were adequately overcome by steadily increasing CPU clock speeds.

Enter 10GbE iWARP

The iWARP extensions to TCP/IP focus on eliminating the three major sources of networking overhead -- transport (TCP/IP) processing, intermediate buffer copies, and application context switches -- that collectively account for nearly 100 percent of CPU overhead related to networking. Specifically, iWARP implements a number of mechanisms to provide a low-latency means of passing RDMA over Ethernet.

The iWARP extensions utilize advanced techniques to reduce CPU overhead, memory bandwidth utilization, and latency by a combination of offloading TCP/IP processing from the CPU, eliminating unnecessary buffering, and dramatically reducing expensive operating system calls and context switches -- moving data management and network protocol processing to an accelerated RDMA over TCP/IP NIC (or R-NIC) 10 Gigabit Ethernet adapter.

R-NICs can reduce CPU utilization for 10 Gbps transfers to less than 10 percent and can reduce the host component of end-to-end latency to as little as 5–10 microseconds. High port-count 10GbE switches are available, which delivers HPC-class latency performance within 100's of nanoseconds.

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