Speed of light is too slow
Los Alamos researchers Brian Albright and Kevin Bowers are part of a team that is developing new numerical simulations to take advantage of a major leap in computing power expected midway through 2008, from an unexpected source: videogame technology.
"Due to physical limitations, such as the speed of light, moving data between and even within modern microchips is more time consuming than performing the actual computations," said Albright of Plasma Theory and Applications (X-1-PTA). "As a result, traditional programming styles are unable to fully exploit the potential of modern 'optimized' microprocessors."
Bowers, also of Plasma Theory and Applications, is presenting his research this week in an invited talk at the annual meeting of the American Physical Society's Division of Plasma Physics in Orlando, Florida.
"Several years ago, a computer code called VPIC was developed at Los Alamos to model plasma physics in a way that takes advantage of these optimized microprocessors and recently was adapted to run on the next iteration of Roadrunner, the newest computer under development by IBM and Los Alamos," said Bowers. "The code has attained unprecedented levels of performance by minimizing the amount of data movement necessary to perform simulations."
The Laboratory is partnering with IBM to reach for the elusive petaflop, equal to a million billion calculations per second. For decades, scientific applications drove the need for higher computer performance, but lately the driving force has not come from science. It comes from the unlikely world of entertainment, via the videogame.
The next generation computing platform at the Laboratory, named Roadrunner, makes heavy use of videogame technology. The upgraded, hybrid architecture of Roadrunner's third phase -- due in the summer of 2008 -- contains both AMD Opteron and IBM Cell Enhanced Double Precision (eDP) processing elements.
Roadrunner is expected to contain 13,000 IBM Cell eDP microprocessors, the same family of processors used in the Sony PlayStation 3. In its current configuration Roadrunner operates at 70 teraflops; when upgraded it is expected to reach a peak performance of more than a petaflop.
The VPIC code is used to do "first principles" simulations, attempting to model the laws of physics with very few assumptions, giving insight to phenomena difficult to recreate in the lab or understand with more approximate theories. According to Bowers, as the performance of microprocessor cores increased rapidly over the past decades, ever larger first principles plasma simulations were possible on a wide range of phenomena, such as plasma instabilities, laser-plasma interaction, magnetic reconnection, space plasma, and magnetic fusion plasma.
When achieved, petaflop performance enables previously impossible simulations in numerous areas of plasma physics, said Albright. For instance, first principles, kinetic, three-dimensional studies of laser-plasma instability inside cavities that form during inertial confinement fusion, a problem of central importance to achieving fusion ignition at Lawrence Livermore National Laboratory's National Ignition Facility, will be possible. Likewise, fully resolved first principles three-dimensional simulations of magnetic reconnection, the biggest unsolved problem in plasma physics and a problem with applicability ranging from astrophysics to magnetic fusion devices, are within reach.
Other topical areas within reach of this capability include ultra-intense laser-matter interaction, space and astrophysical plasmas, shocks, radiographic source modeling, plasma turbulence, and thermonuclear burning plasma media.
