China expands presence on Top 500 list

SAN JOSE, Calif. – China not only kept its number one spot in the latest rankings of the Top 500 supercomputers, it extended its reach deeper on the list. It now has 42 of the world's most powerful computers, surpassing France, Germany, Japan and the UK and is second only to the U.S.

The rankings, released at the opening of the Supercomputing 2010 in New Orleans, show Intel's x86 processors still dominate the list, but archrival AMD made some gains. But a growing number of supercomputers--28 on the latest list--pair such chips with graphics processors to boost performance and keep a lid on power consumption.

The hybrid systems include Tianjin's Tianhe-1a, the world's most powerful system measured at 2.5 petaflops on the Linpack benchmark. The third highest performance system at 1.27 Pflops is also a hybrid, the Nebulae built by Dawning Information Industry Co. in Shenzhen.

"I think there will be a lot of discussion of the Tainhe-1a because it’s the first system at the top both to use GPUs and to come from China," said William Dally, chief scientist at GPU maker Nvidia whose chips power the system. "The machine is an impressive development in absolute performance and in the homegrown technology in its network and physical design," said Dally.

Researchers behind the Tianhe-1a have yet to reveal details of Galaxy, the proprietary 160 Gbit/second interconnect that helps fuel its performance. "I am very interested in how they attacked the more nuanced issues," said Dally who for nearly twenty years has helped design interconnects for U.S. supercomputer company Cray.

The Tianhe-1a "is an engineering feat--we know how hard it is to build a petascale system, but I can't comment on how sustainable its performance is" under real workloads, said Barry Bolding, vice president of Cray's products group.

Researchers have yet to reveal bandwidth and latency figures for Galaxy when the interconnect is under stress of running scientific applications. Details such as random ring latency in such conditions are more telling than the maximum theorthetical throughput China reported, said Bolding.

The Linpack benchmark used as the basis for the Top 500 list itself has been widely criticized as limited even by the researchers who maintain the list.

"People have used Linpack because it is convenient and relatively easy to run, but Linpack is not very representative of machines today," said Dally. "It’s a good proxy for dense linear algebra, but some apps don’t use that and supercomputer workloads are becoming more diverse," he added.

The U.S. remains the leading supercomputer user with 275 of the top systems, down from 282 on the June list. Europe's share dropped to 124 systems from 144. Germany and Japan tied for the third spot behind China with 26 systems each.