Applications
Applications
To support one of the Grand Challenge teams in achieving the ESS Project's milestones by providing technical assistance in parallelization and optimization of their applications, assuring that the projects can succeed in their goals, and verifying that their milestones have been met. The team's project is "Development of an Earth System Model (ESM), Including Atmosphere (AGCM), Ocean (OGCM) and Atmospheric Chemistry Tracer (ACTM)" (PI: Professor Roberto Mechoso, University of California, Los Angeles).
Additional performance optimization efforts on various components of the ESM model have been made this year to meet the second performance milestone, defined by running the coupled atmosphere/ocean/chemistry code at four times the speed for the first milestone. Work on the AGCM/ACTM code includes performing load-balancing for polar filtering at a finer level to achieve better result on large number of processing nodes on CRAY T3E, the use of a different version of the AGCM/Physics algorithm in which the cloud-scale kinetic energy (CKE) is predicted rather than dynamically computed as in the original scheme, and the use of STREAM facility on Cray T3E. The new AGCM/Physics algorithm is physically the same in some time-averaged sense as the original one, but it is simpler and computationally more efficient, and the cache-miss rate is significantly reduced. Work was also done to develop a Distributed Data Broker to couple the AGCM, ACTM, and OGCM into an ESM model. Support for the Development of an Earth System Model project this year has been mainly in the form of keeping interactions with the UCLA team members, discussing problems they faced in achieving milestone objectives, including various performance issues and the Distributed Data Broker, and offering suggestions on possible solution approaches.
Technical suggestions were provided on code performance optimizations on the CRAY T3E system at Goddard Space Flight Center. Verification of the second performance milestone submission from UCLA's Earth System Modeling team was completed. In the verification process, we discussed with and provided suggestions to the UCLA team on the content of their submission to meet the requirements for their milestone submission by the project management. A paper by John Lou and John Farrara, titled "Performance Analysis and Optimization on a Parallel Atmospheric General Circulation Model Code" is being published in the Journal of Concurrency, Practice ,and Experience in August 1998.
A computationally efficient, coupled Earth system modeling code is significant to both the ESS Project as a technology-enabling program and to the Earth system modeling research. Our support for the Development of an Earth System Model project in parallel performance optimization in terms of algorithm and code development has been an important factor in their success of reaching the ESS Project milestones.
In June, 1998, UCLA's ESM team made their second performance milestone submission, in which they ran a coupled Earth System Model code (including AGCM, ACTM and OGCM) with a centralized data broker on 787 nodes of a Cray T3E at GSFC, and achieved a performance four times faster than that achieved for their first performance milestone. What remains to be done, in terms of performance milestones, is the completion of a fully functional and scalable distributed data broker for the coupled ESM model. We will work with the UCLA team closely and provide any help they need to achieve this goal.
John Z. Lou
NASA Jet Propulsion Laboratory
lou@acadia.jpl.nasa.gov
818-354-4870