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June 13, 2013

Titan Didn’t Redo LINPACK for June Top 500 List

Alex Woodie

Titan, the Cray XK7 at the Oak Ridge National Lab that debuted last fall as the fastest supercomputer in the world with 17.59 petaflops of sustained computing power, will rely on its previous LINPACK test for the upcoming edition of the Top 500 list.

The 560,000-core Titan had little chance of retaining the number one spot on the June 2013 Top 500 list, which will be unveiled at the International Supercomputing Conference next week in Germany. China’s massive Tianhe-2, with 3.1 million cores and a reported 31 petaflops of sustained capacity, will take the top spot on the list, barring any unforeseen events.

While Titan likely could have improved its performance on the LINPACK test that determines one’s place on the Top 500 list, it was apparently not worth the effort.

“To be honest, we decided at this point not to waste any more time,” Jeff Nichols, Oak Ridge’s scientific computing chief, told blogger Frank Munger. “We know that the Chinese machine is going to blow us out of the water.”

Titan could have made an iterative improvement on the LINPACK test, perhaps stretching its results to 19 to 20 petaflops. The machine, which uses a combination of Opteron CPUs and Nvidia GPUs, has a theoretical peak of 27 petaflops. Tianhe-2, which consumes 24 MW of power (compared to Titan’s 8.2 MW), has a theoretical peak of 49 petaflops.

Instead of taking a week to rerun LINPACK, Nichols and others at Oak Ridge decided it was better to use Titan to do the scientific work that it was built to perform, rather than compete for ranking.

Titan burst on the scene last November, when it pushed Sequoia, the IBM BlueGene/Q supercomputer installed at Lawrence Livermore National Lab, out of the top spot. Sequoia, which debuted on the list in November 2011 with 677 terraflops with only 65,000 Power cores running, moved up to the number one spot in June 2012, when it had its full complement of 1.57 million cores pushing 16.3 petaflops.

While not every top HPC system reruns LINPACK every six months, some top supercomputers have opted out of the Top 500 rankings altogether. Blue Waters, the Opteron- and Nvidia-based Cray supercomputer that recently went online at University of Illinois Urbana-Champaign, will not run LINPACK participate in the Top 500 list. It has 11.5 petaflops of capacity, but the administrators in charge of Blue Waters prefer to do actual research, instead of taking the time to tune the system for a favorable LINPACK result.

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