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GCN Home > 03/06/06 issue

When are supercomputers really super?

Interconnect speed is key to high-performance computing

By Joab Jackson, GCN Staff

When the Energy Department’s National Energy Research Scientific Computing Center went shopping for a new mid-sized supercomputer, processor speed was a critical factor, as expected. But it also carefully scrutinized the interconnect speeds of the proposed systems. That’s because for this supercomputing center, the speed of the conduit between processors was as important as the speed of the CPUs themselves.

“The interconnect is important because a lot of the applications rely on low latency and high bandwidth,” said Bill Kramer, NERSC general manager. “We run highly parallel applications. One application may make use of 50 or 100 individual nodes.”

Because high-performance computing applications are increasingly spread out over so many processors, how fast they perform comes down in large part to how fast individual nodes can communicate with one another.

Not surprisingly, HPC interconnect makers are jockeying to show who has the speediest, most cost-effective technology for connecting nodes. The field is awash in different adapters, both proprietary and standards-based, and comparing them can be a challenge for even the most adept system architect. And confusing matters even more is the industry practice of tweaking performance results so speed figures look more competitive, and less indicative of what users may actually see. In short, finding the fastest HPC technology takes more than scanning the list of the Top 500 supercomputers (www.top500.org).

“You definitely have to understand what is being measured,” said Greg Thorson, principal engineer for platform development at SGI of Mountain View, Calif. Shortly after PathScale Inc. of Mountain View, Calif., released its new InfiniPath networking adapter, it dispatched its distinguished scientist Greg Lindahl to give a presentation at a Beowulf Users Group meeting in Washington.

PathScale was not the first HPC interconnect vendor to court the group, which comprises a small but technically savvy collection of HPC system managers, including several from government agencies. SGI, Foundry Networks Inc. of San Jose, Calif., InfiniCon Systems Inc. of King of Prussia, Pa., and Voltaire Inc. of Billerica, Mass., also have presented to the Beowulf group. (Beowulf is a Linux-based clustering platform—and an Old English poem).

In addition to touting the benefits of his company’s own interconnect, which is based on the InfiniBand standard, Lindahl warned of the potential pitfalls of comparing performance claims.

More news on related topics: Communications / Networks, Hardware



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