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Advancements in SciDAC Software API for High-Performance Lattice QCD Computing

This document outlines the goals and structure of the SciDAC Software API, as presented by Robert Edwards and other members of the U.S. SciDAC Software Coordinating Committee. The API focuses on developing portable, scalable software optimized for high-performance computing on QCDOC clusters and other architectures. Key features include infrastructure for the U.S. national community, data management for lattice data, and advanced operations with flexibility across different platforms. Ongoing efforts to enhance performance and streamline data handling are also covered.

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Advancements in SciDAC Software API for High-Performance Lattice QCD Computing

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  1. I/O and the SciDAC Software API Robert Edwards U.S. SciDAC Software Coordinating Committee May 2, 2003

  2. Cast of Characters Committee:R.Brower, C.DeTar,R.Edwards, D.Holmgren, R.Mawhinney, C.Mendes,C.Watson Additional: J.Chen,E.Gregory,J.Hetrick, C.Jung, J.Osborn, K.Petrov, A.Pochinsky, J.Simone IO:C.DeTar,R.Edwards, J.Osborn, J.Simone, B.Joó

  3. entific iscovery Through dvanced omputing Sci D A C http://www.lqcd.org/scidac

  4. QCDOC Clusters GRID (ILDG) SciDAC Project Goals • Portable, scalable software • High performance optimization on two target architectures • Exploitation and Optimization of existing application base • Infrastructure for (US) national community • Sharing of valuable lattice data, and data management

  5. Optimised for P4 and QCDOC Optimised Dirac Operators, Inverters Level 3 QDP (QCD Data Parallel) QIO Lattice Wide Operations, Data shifts XML I/O DIME Level 2 Exists in C/C++ QLA (QCD Linear Algebra) Level 1 Focus of talk QMP (QCD Message Passing) Exists in C/C++, implemented over MPI, GM, QCDOC, gigE SciDAC Software Structure

  6. Data Parallel QDP/C,C++ API • Hides architecture and layout • Operates on lattice fields across sites • Linear algebra tailored for QCD • Shifts and permutation maps across sites • Reductions • Subsets

  7. Unary and binary: -a; a-b; … Unary functions: adj(a), cos(a), sin(a), … Random numbers: // platform independent random(a), gaussian(a) Comparisons (booleans) a <= b, … Broadcasts: a = 0, … Reductions: sum(a), … Data-parallel Operations

  8. QDP Expressions • Can create expressions • QDP/C++ code multi1d<LatticeColorMatrix> u(Nd); LatticeDiracFermionb, c, d; int mu; c = u[mu] * shift(b,mu) + 2 * d; • PETE: Portable Expression Template Engine • Temporaries eliminated, expressions optimised

  9. Generic QDP Binary File Formats • Composed of 1 or more application records • Single application record has 1 QDP field or an array of fields • Binary data in lexicographic site major order • Physics metadata for file and for each record • Using DIME to package

  10. Metadata • Use XML for file and record metadata • File and record metadata managed at user convenience • No agreed minimum standard • Use binX to describe binary • binXnot in record metadata – provides serialization info

  11. Gauge Fields • For publisheddata – still converging on metadata • Considering adopting ILDG-like schema • Need more cases, like Asqtad, domain wall • Likely that non-published/private configs will use reduced set of metadata • Write arrays of fields as one record – all 3 rows • Site major order – slowest varying • Will adopt single format and byte ordering

  12. File Format • File physics metadata • Application record 1 • Physics metadata • binX description • Binary data [may have array indices within sites] • Checksum • Record 2 - possible additional records • Physics metadata • binX description • Binary data • Checksum • Record 3….

  13. Data Hierarchy • Project built from datasets (e.g. gauge fields and propagators) • Dataset built from files (e.g. gauge fields) • File built from records (e.g. eigenvectors) • Record = QDP field and metadata

  14. DirectInternetMessageEncapsulation(DIME) • Data written to (read from) a list of records • Each record has • DIME Type (required) • URL or like MIME type • DIME Id (optional URL) • Maximum record size is 2Gb • Data larger than 2Gb can be split into successive record “ chunks” • Chunking easy, file size > 2Gb a problem

  15. QIO: Grid Friendly I/O • Metadata & Physics data Reader / Writer API • Read/Write simple XML documents • Not using data binding • Metadata used like a buffer, physics data like a stream • QDP IO (QIO) • Serial– all nodes stream through one node • Parallel– if available, many nodes to parallel filesystem MetaWriterfile_xml, record_xml; SerialFileWriter out(file_xml,“foo.dat”); LatticeDiracFermion psi; out.write(record_xml, psi);

  16. MetaReader File xml: struct foo_tfoo; struct bar_tbar; doublekappa; MetaReaderin; char *key=”/foo/bar/kappa”; <foo> <bar> <kappa> 0.120 </kappa> </bar> </foo> in.get<foo_t>(foo,“/foo”) in.get<double>(kappa,key); • XML Reader/Writer supports recursive serialization • To/From buffers (strings - MetaData) • To/From files (PhysicsData) • Intended to drive codes rather than DataGrid • C,C++ versions

  17. Current Status • Releases and documentation http://www.lqcd.org/scidac • QMP, QDP/C,C++ in first release • Performance improvements/testing underway • Porting & development efforts of physics codes over QDP on-going • QIO near completion • DIME completed (Bálint Joó) • XML Reader/Writer in development

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