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Computational Design of the CCSM Next Generation Coupler

Computational Design of the CCSM Next Generation Coupler. Tom Bettge Tony Craig Brian Kauffman National Center for Atmospheric Research Boulder, Colorado USA.

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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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