November 7-8, 1996

Cray Research, Eagan, MN

November 7, 1996

Mike Heroux and Jack Dongarra opened the meeting by welcoming everyone and inviting everyone to introduce themselves. It was then asked if we should continue the BLAST Forum meetings? The consensus was that we wish to continue the meetings but that we need the subgroups to be more focused and more active.

The following presentations were made:

BLAS functionality was the first to be addressed. Sven Hammarling of NAG gave a brief overview of the Functionality proposal that has been available via the BLAS Forum homepage. Tony Skjellum argued that the present form of the proposal is too broad and that it should be more sharply focused on functionality. Issues such as implementations, performance, and language interfaces should be covered separate proposals. Linda Kaufman suggested, and several others concurred, that each of the proposed ``new'' BLAS routines should be assigned a priority indicating the importance of its inclusion. Most participants felt that routines to generate Givens rotations and Householder transforms should have top priority. As the discussion continued it was decided that this topic would be best addressed at the subgroup meeting and the results presented at the general meeting of all participants.

Tony Skjellum then led the discussion on the proposal for the BLAS Lite. Some notational confusion ensued surrounding the definition of ``lite'' versus ``thin''. In future discussions, ``lite'' will refer to low-level primitive functions, whereas ``thin'' will refer to interfaces that do not provide overloaded functionality. The BLAS Lite as presented by Skjellum are intended to be basic low-level building blocks for constructing portable high-performance linear algebra functions. Key compiler and processor technologies such as inlining, data prefetching, unrolling, and so forth, would be exploited to obtain both high-performance and portability. Two versions of the BLAS Lite were proposed. One (debugging) version with error-checking, and another (performance) version without error-checking. To provide good performance on all problem sizes, separate interfaces for stride 1 operations may be provided, as well as separate routines for small (block) problems, e.g., matrix multiplies of size 16.

After a break, Sven Hammarling next proposed the Fortran 90 interface to the BLAS Lite. He reviewed the motivations of the project which are no error checking, no character arguments, and no run-time tests. He then presented the Fortran90 interface with its use of generic interfaces, assumed shape arrays, optional arguments, and modules. He proposed the combining of the Level 2 and 3 BLAS into a generic interface.

Jack Dongarra then led discussion on a proposed interface for the Parallel BLAS and stressed the need to establish a standard in this area. This proposed object-based interface allows the accommodation of different data distributions and is not restricted to two-dimensional data distribution. It was pointed out that a new descriptor type could be assigned for the physically based matrix distribution (PBMD), thereby allowing a different vector distribution if the process grid is two-dimensional. Tony Skjellum contended that one could obtain high-performance via redistribution of data (at the cost of extra memory). Mike Heroux commented that for many customers, there is no memory to spare. Mike Heroux of Cray and Sven Hammarling of NAG seconded this need to address standards for the parallel BLAS.

Roldan Pozo and Karin Remington of NIST next presented the NIST Sparse BLAS Toolkit. They stressed the need for user feedback, and presented their observations of sparse BLAS work. These observations were that there was no performance difference between ``thin'' and ``fat'' interfaces. The ``thin'' interface yields over 1,200 functions. Based on the higher flop rates obtained using block structured matrices, Roldan and Karin concluded that performance is more a factor of matrix structure rather than algorithmic tweaks --- in fact, it is typically best to transform the matrix into block structure first. Andrew Lumsdaine brought up issues of performance and contended that abstraction does not per se hurt performance and that a complete C++ implementation could obtain performance better than the NIST model implementation. Detailed performance information for the NIST Sparse BLAS implementation is available on the web. Issues of sparse benchmarks then arose, with Tony Skjellum suggesting that a careful study be made.

November 8, 1996

Mike Heroux and Jack Dongarra opened the morning session with a continuation of the presentations from the preceding day.

Linda Kaufman and Andy Anda presented their ideas for extensions to the existing BLAS and defined a priority for each of the proposed routines. Linda expressed her fear that too many routines are being proposed as extensions, and suggested that each routine be prioritized. Linda felt that the most important routines were for Householder transformations, SAMAXs, WAXPYs, simultaneous ISAMAXs, simultaneous SAXPYs, simultaneous SVDs, and simultaneous Givens transformations. She then presented a variety of applications for sparse matrices in which she stressed that a lot of users do not want to explicitly store the sparse matrix. Andy Anda stressed the need for routines to generate and apply rotations.

Andrew Lumsdaine next spoke about language bindings and their need between applications and language interfaces, as well as at the lower level between the library and the BLAS. The path to these bindings specifies the functionality, abstractions, language independent functions, and the question of interoperability between languages. However, he stressed that language binding issues should be considered toward the end of the process of these meetings. They cannot be adequately addressed at the beginning.

The meeting then took a short break as the participants were invited to tour the Cray machine room.

After lunch, the meeting continued with vendor presentations. Specifically, the following vendors:

The vendors expressed concern about the volume of routines that are proposed, and the necessity of reference implementations and documentation for each of the proposed routines.

Sven Hammarling of NAG presented a brief synopsis of the contents of the NAG Fortran Library, Fortran90 Library, C Library, and the Parallel Library. He stressed that the BLAS have been vital to the portability of the libraries that they offer their customers, and further cited the need for standardization of the PBLAS as parallel packages are increasingly being requested by users. He also cited the need for standardization of FFTs.

Theresa Do and Sandra Carney of Cray Research spoke of the Silicon Cray Scientific Library and the need for standards for single PE performance. Sandra further presented a comparison of sparse storage schemes, and which ones are used most often by users. She also suggested that the future is evolving toward random sparse matrices.

Chandrika Kamath of Digital Equipment Corporation presented an overview of the DXML package. She stressed that users wanted pre-defined storage schemes for sparse matrices used in iterative solvers. While experienced users were comfortable with a matrix-free formulation, and even requested such an interface, novice users had difficulty understanding the concept.

Hsin-Ying Lin of HP/Convex Corporation spoke of the MLib library for HP S-class computers. He stressed that the priorities of the math software library group are application driven due to limited resources. He listed these priorities in the order of importance as: DGEMM/DGEMV, dot products, saxpys, blas-1 operations, sparse BLAS, FFT/convolutions, LAPACK, and SCILIB/Skyline. He stressed the need for reference implementations and complete documentation for new proposals.

Shane Story of Intel Corporation spoke of the math library for Intel MP node machines provided by their Independent Software Vendor (ISV) -- Kuck and Associates. Basically, Intel does not support a math libraries group anymore, and instead hires third-party vendors to write software for their machines. They plan to tune existing libraries for their machines, and not provide any additional functionality.

Cormac Garvey of NEC primarily discussed mathematical software targeted for the NEC SX-4 class of machines. He stressed that third-party applications and public domain software are driven by customer requirements. He attends the BLAST forums to be aware of the new standards that are developing. They plan to support Fortran77, Fortran90, C, C++, HPF, and MPI applications in their libraries. And in the future they plan to support sparse BLAS and parallel BLAS. He prefers an approach to the meetings looking at applications. And he asked the question of why aren't third-party software developers using BLAS? He felt that we need participation by more ISVs.

Joan McComb of IBM spoke of the ESSL and PESSL mathematical packages available for their machines. The priorities of their math library development are focused on the demands of the customers' applications. She primarily focused on the customers' request for HPF support, and with this the need for standardization of the parallel BLAS.

Summaries of the meeting were then provided by Mike Heroux, Tony Skjellum, and Jack Dongarra.

Mike Heroux summarized by presenting his library development perspectives. He felt that we should consider the following points:

  1. What is the value of the BLAS?
  2. Where are the BLAS used?
  3. Impact if no BLAS?
  4. Old applications versus new applications?
  5. Alternative standardization?

He stressed that we should consider the value added by the BLAS, specifically in providing performance with immature compilers. The BLAS are primarily used in computational chemistry and eigenvalue computations, and have a modest use in finite-element (FEM) codes. They are used little elsewhere in third-party codes. As for the impact if there were no BLAS, he suggested that the impact would not be as great as we would like. He felt that the major impact of no BLAS would be the improvement of optimization in compilers. As for the need for BLAS in old applications versus new applications, he stressed that we need to see what's useful in a broad spectrum of codes. There are dangers in using current applications as a target. And finally, he suggested that perhaps we should consider alternative standardizations.

Tony Skjellum presented sample implementations of the BLAS Lite to help clarify the previous day's confusion on ``lite'' and ``thin''. He also suggested that we eliminate plenary meetings and that we only need to meet in subcommittees. He was concerned that there are not enough application developers, so these technical forums do not adequately represent their views. We need participation in these meetings by ISVs. The ISVs do not use the BLAS or LAPACK, and the hardware vendors are increasingly using these third-party code organizations to supply software for their machines. Should we limit the scope/focus of these meetings to only linear algebra kernels? He suggested an application-based study of the needs of the community.

Jack Dongarra wrapped up the meeting by suggesting that the following subgroups and subgroup leaders should meet, communicate with the ISVs and application developers, and bring their proposals back to the plenary committee.

The former major domo mailing aliases will be reset with the existing members being put into the blast-comm alias. The new major domo mailing aliases shall be: blast-funct, blast-lite, blast-parallel, blast-sparse, blast-lb, blast-nearterm.

The global editors are Andrew Lumsdaine and Tony Skjellum.

The tentative date of the next forum meeting is:

with a preliminary deadline of January 15, 1997 for subgroup progress.

The meeting was then adjourned by Mike Heroux and Jack Dongarra at 2:30 PM.

Attendees list for the November 7-8, 1996 BLAST Forum Meeting

Andy Anda                             
Ed Anderson          Cray Research   
Puri Bangalore       Miss. State Univ.
Susan Blackford      Univ. of TN, Knoxville
Sandra Carney        Cray Research   
Samar Choudhary      Cray Research   
Edmond Chow          Univ. of MN      
Theresa Do           Cray Research   
Jack Dongarra        Univ. of TN / ORNL
Cormac Garvey        NEC Systems Laboratory
John Gunnels         Univ. of TX, Austin 
Sven Hammarling      NAG, UK         
Mike Heroux          Cray Research    
Linda Kaufman        Bell Labs       
Chandrika Kamath     DEC             
Guangye Li           Cray Research   
Hsin-Ying Lin        HP Convex Technology Ctr.
Andrew Lumsdaine     Univ. of Notre Dame
Brian McCandless     Univ. of Notre Dame
Joan McComb          IBM Poughkeepsie
Tom Oppe             Cray Research    
Roldan Pozo          NIST            
Karin Remington      NIST             
Tony Skjellum        Miss. State Univ.
Shane Story          Intel            
Chuck Swanson        Cray Research   
Robert van de Geijn  Univ. of TX, Austin
Clint Whaley         Univ. of TN, Knoxville

Susan Blackford and Andrew Lumsdaine agreed to take minutes for the meetings.