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Computational Design of the CCSM Next Generation Coupler

Explore the design and functionalities of the Next Generation Coupler (NGC) for advanced high-performance computing facilities, addressing current shortcomings and future improvements in climate modeling. Learn about the formal design process, computational requirements, and key features of the NGC. Discover how the Model Coupling Toolkit and Multi-Component Handshaking Library enhance component communications and data transfer for better model integration.

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Computational Design of the CCSM Next Generation Coupler

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  1. Computational Design of the CCSM Next Generation Coupler Tom Bettge Tony Craig Brian Kauffman National Center for Atmospheric Research Boulder, Colorado USA Draft Presentation: The Fourth International Workshop on Next Generation Climate Models for Advanced High Performance Computing Facilities, March 12-14, 2002, Boulder, Colorado, USA.

  2. Background 1:Current Coupler Shortcomings • CSM1 load balancing • Parallel Climate Model (PCM) scalability • Flexibility • Extensibility • Portability? • CSM1 designed primarily for vector architectures • PCM designed primarily for distributed memory single/multiprocessor clusters • Code reuse: poor

  3. Background 2:Future Coupler Design • New CCSM Coupler:Next Generation Coupler (NGC) • DOE/NSF Proposal • Performance-Portable Extendible Coupler • scientific requirements • computational requirements • Formal Software Development Process • isolate requirements (Spring 2000) • state a design (abstractions, code reuse, etc.) • prototyping • code construction • testing and validation www.ccsm.ucar.edu/models/cpl6

  4. NGC Requirements:Scientific Functionality • Provide overall control of coupled system • Flexible and extensible: new components, new exchange information • Flexible coupling frequencies • Process split or time split advancement • Allow computations • compute interfacial fluxes • mapping between grids • merging of information • temporal accumulation and averaging • diagnostics • Process data on a variety of grids

  5. NGC Requirements:Computational Functionality • Portable • Language: F90 or F90 interfaces • Parallelism • pure shared memory • pure message passing • hybrid • Flexible coupler/model interface • Sequential or concurrent model execution • Build as single or multiple executables • I/O capability • Error handling

  6. NGC Design:Considerations • high level command/control • lower level functions --> suggests a layered design strategy • concurrent or sequential execution • flexibility • generalized error handling --> suggests a library core of functions • generalized grid representations • extensibility --> suggests internal derived data types

  7. Next Generation CouplerFormal Design cplx (cpl6) MCT* MPH** *Model Coupling Toolkit ** Multi-Component Handshaking Library

  8. MPEU – Message Passing Env Utility From NASA DAO, provides the following services: • F90 module-style access to MPI • Portable/Flexible definition of types • Support for multiprocessor stdout/stderr • Error handling / shutdown • Timing/Load balance monitoring tools • Sorting Tools • Support for basic derived types on which low-level classes in the MCT are built Code used as scaffolding, but utilities might fit well in CCSM.

  9. MCT - Model Coupling Toolkit Major Attributes: • Maintains model decomposition descriptors (e.g., global to local indexing) • Inter- and intra- component communications and parallel data transfer (routing) • Flexible, extensible, indexible field storage • Time averaging and accumulation • Regridding (via sparse matrix vector multiply) The MCT eases the construction of coupler computational cores and component-coupler interfaces. www-unix.mcs.anl.gov/acpi/mct

  10. MPH - Multi-Component Handshaking Library General Features • built on MPI • establishes MPI communicator for each component • performs component name registration • allows resource allocation for each component • supports different execution modes www.nersc.gov/research/SCG/acpi/MPH

  11. cplx Architecture

  12. Component Model/Coupler Interface Use coupler interface modules: use module ngc_interface_mod.F90 use module ngc_fields_mod.F90 Compile/link shared code (cpl6 modules, MCT, MPH) with model. Calls: ngc_init( modelID, localComm ) ngc_sendInit( modelID, flags(:), buffer(:,:) ) ngc_recvInit( modelID, flags(:), buffer(:,:) ) ngc_send( modelID, flags(:), buffer(:,:) ) ngc_recv( modelID, flags(:), buffer(:,:) ) ngc_sendFin( modelID, flags(:), buffer(:,:) ) ngc_finalize( modelID )

  13. cpl6 Implementation • Initial cpl6 - same interactions as cpl5 • Concurrent component execution • Multiple executables • Message passing will be distributed parallel • Matrix multiply will be distributed parallel

  14. cpl6 Coupling Procedure/Issues • multiple executable, concurrent execution (CCSM2)

  15. Coupled System Processor Layout CCSM2 PCM CSM1 Target?

  16. Schedule and FAQ • cpl6 prototype – exists • cpl6beta – June 2002 • cpl6 – Fall 2002 • Will cpl6 be the coupler in the May 2002 CCSM2 release? No. The first release of CCSM2 will contain cpl5. • Will cpl6 offer new functionality over cpl5? No. For the most part, cpl6 replicates cpl5 functionality. However, the new coupling framework provides the tools to easily build differing instantiations of a “coupler”. cpl6 is one such instantiation (e.g.., cpl6 is distributed parallel)

  17. cpl [next] • cpl[next] charter? • user community input to whom? (no coupler WG) • process for introducing/requesting/prioritizing new features • features? • “on the fly” SCRIP (multiple options) • CCSM single binary, sequential executable cpl • cpl suitable for cluster of vector machines • concept of one model, multiple grids?

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