NASA Evaluates Cell for Climate Modeling

Thursday 31st July 2008, 05:18:00 PM, written by Carl Bender

At last month's International Supercomputing Conference in Dresden, NASA presented the results of an internal study exploring the suitability of the Cell BE architecture towards accelerating key aspects of climate modeling.  Centered on the computationally intensive solar radiation component of the Goddard Earth Observing System Model v5 (GEOS-5), the study required that roughly 2,000 lines of Fortran be ported to C in order to run on the Cell's SPEs.  As the data in question benefited from computational independence, it was vectorized as well to result in four columns of data mapped to each of the eight SPEs present on-chip. The Cell was in turn able to work through over 3,000 columns of data per second, across all test cases.

When run on a QS20 Cell blade provided by the UMBC Multicore Computational Center, significant single processor performance gains were recorded against Intel architectures presently in use by the NASA Center for Computational Sciences.  Running the maximum test case of 1,024 data columns, Cell showed a 6.76x improvement against Woodcrest@2.66GHz.  Against Dempsey@3.2GHz the improvement was 8.91x, and against an Itanium 2 running at 1.5GHz, Cell demonstrated a 9.85-fold improvement.  The comparisons were kept single-core due to the non-linear performance scaling of the Intel architectures, with the Intel architectures running the baseline Fortran as opposed to the ported C. 

All comparisons were for single precision performance, as the study predates the introduction of the PowerXCell 8i.  The study was conducted before the introduction of a Cell Fortran compiler and auto-SIMD tools as well, both of which have since seen release by IBM in calendar 2008.  It was with that knowledge in mind, however, that a relatively light ~2,000 line portion of code was chosen to serve as a testbed. 

Having shown positive results on solar radiation, the team is now exploring further code porting for the computationally similar moisture, chemistry, and turbulence physics models; collectively these types of physics problems account for ~50% of GEOS-5 compute time.  In addition, project lead Shujia Zhou has been working on a hybrid solution towards allowing Fortran to be run directly on the Cell processor. 

A session at the 2008 American Geophysical Union Fall Meeting this December entitled "Emerging Multicore Computing Technology in Earth and Space Sciences" should serve as the next window into their progress.

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