Section: Scientific Foundations
Parallel Programming on Peer-to-Peer Platforms (P5)
Several scientific applications, traditionally computed on classical parallel supercomputers, may now be adapted for geographically distributed heterogeneous resources. Large scale P2P systems are alternative computing facilities to solve grand challenge applications.
Peer-to-Peer computing paradigm for large scale scientific and engineering applications is emerging as a new potential solution for end-user scientists and engineers. We have to experiment and to evaluate such programming to be able to propose the larger possible virtualization of the underlying complexity for the end-user.
Large Scale Computational Sciences and Engineering
Parallel and distributed scientific application developments and resource managements in these environments are a new and complex undertaking. In scientific computation, the validity of calculations, the numerical stability, the choices of methods and software are depending of properties of each peer and its software and hardware environments; which are known only at run time and are non-deterministic. The research to obtain acceptable frameworks, methodologies, languages and tools to allow end-users to solve accurately their applications in this context is capital for the future of this programming paradigm.
GRID scientific and engineering computing exists already since more than a decade. Since the last few years, the scale of the problem sizes and the global complexity of the applications increase rapidly. The scientific simulation approach is now general in many scientific domains, in addition to theoretical and experimental aspects, often link to more classic methods. Several applications would be computed on world-spread networks of heterogeneous computers using some web-based Application Server Provider (ASP) dedicated to targeted scientific domains. New very strategic domains, such as Nanotechnologies, Climatology or Life Sciences, are in the forefront of these applications. The development in this very important domain and the leadership in many scientific domains will depend in a close future to the ability to experiment very large scale simulation on adequate systems  . The P2P scientific programming is a potential solution, which is based on existing computers and networks. The present scientific applications on such systems are only concerning problems which are mainly data independents: i.e. each peer does not communicate with the others.
P2P programming has to develop parallel programming paradigms which allow more complex dependencies between computing resources. This challenge is an important goal to be able to solve large scientific applications. The results would also be extrapolated toward future petascale heterogeneous hierarchically designed supercomputers.
Experimentations and Evaluations
We have followed two tracks. First, we did experiments on large P2P platforms in order to obtain a realistic evaluation of the performance we can expect. Second, we have set some hypothesis on peers, networks, and scheduling in order to have theoretical evaluations of the potential performance. Then, we have chosen a classical linear algebra method well-adapted to large granularity parallelism and asynchronous scheduling: the block Gauss-Jordan method to invert dense very large matrices. We have also chosen the calculation of one matrix polynomial, which generates computation schemes similar to many linear algebra iterative methods, well-adapted for very large sparse matrices. Thus, we were able to theoretically evaluate the potential throughput with respect to several parameters such as the matrix size and the multicast network speed.
Since the beginning of the evaluations, we experimented with those parallel methods on a few dozen peer XtremWeb P2P Platforms. We continue these experiments on larger platforms in order to compare these results to the theoretical ones. Then, we would be able to extrapolate and obtain potential performance for some scientific applications.
Recently, we also experimented several Krylov based method, such as the Lanczos and GMRES methods on several grids, such as a French-Japanese grid using hundred of PC in France and 4 clusters at the University of Tsukuba. We also experimented on GRID5000 the same methods. We currently use several middleware such as Xtremweb, OmniRPC and Condor. We also begin some experimentations on the Tsubame supercomputer in collaboration with the TITech (Tokyo Institute of Technologies) in order to compare our grid approaches and the High performance one on an hybrid supercomputer.
Experimentations and evaluation for several linear algebra methods for large matrices on P2P systems will always be developed all along the Grand Large project, to be able to confront the different results to the reality of the existing platforms.
As a challenge, we would like, in several months, to efficiently invert a dense matrix of size one million using a several thousand peer platform. We are already inverting very large dense matrices on Grid5000 but more efficient scheduler and a larger number of processors are required to this challenge.
Beyond the experimentations and the evaluations, we propose the basis of a methodology to efficiently program such platforms, which allow us to define languages, tools and interface for the end-user.
Languages, Tools and Interface
The underlying complexity of the Large Scale P2P programming has to be mainly virtualized for the end-user. We have to propose an interface between the end-user and the middleware which may extract the end-user expertise or propose an on-the-shelf general solution. Targeted applications concern very large scientific problems which have to be developed using component technologies and up-to-dated software technologies.
We introduced the YML framework and language which allows to describe dependencies between components. We introduced different classes of components, depending of the level of abstraction, which are associated with divers parts of the framework. A component catalogue is managed by an administrator and/or the end-users. Another catalogue is managed with respect to the experimental platform and the middleware criteria. A front-end part is completely independent of any middleware or testbed, and a back-end part is developed for each targeted middleware/platform couple. A YML scheduler is adapted for each of the targeted systems.
The YML framework and language propose a solution to develop scientific applications to P2P and GRID platform. An end-user can directly develop programs using this framework. Nevertheless, many end-users would prefer avoid programming at the component and dependency graph level. Then, an interface has to be proposed soon, using the YML framework. This interface may be dedicated to a special scientific domain to be able to focus on the end-user vocabulary and P2P programming knowledge. We plan to develop such version based on the YML framework and language. The first targeted scientific domain will be very large linear algebra for dense or sparse matrices.