An MPI-CUDA Implementation for Massively Parallel Incompressible Flow Computations on Multi-GPU Clusters

Modern graphics processing units (GPUs) with many-core architectures have emerged as general-purpose parallel computing platforms that can accelerate simulation science applications tremendously. While multi-GPU workstations with several TeraFLOPS of peak computing power are available to accelerate computational problems, larger problems require even more resources. Conventional clusters of central processing units (CPU) are now being augmented with multiple GPUs in each compute-node to tackle large problems. The heterogeneous architecture of a multi-GPU cluster with a deep memory hierarchy creates unique challenges in developing scalable and efficient simulation codes. In this study, we pursue mixed MPI-CUDA implementations and investigate three strategies to probe the efficiency and scalability of incompressible flow computations on the Lincoln Tesla cluster at the National Center for Supercomputing Applications (NCSA). We exploit some of the advanced features of MPI and CUDA programming to overlap both GPU data transfer and MPI communications with computations on the GPU. We sustain approximately 2.4 TeraFLOPS on the 64 nodes of the NCSA Lincoln Tesla cluster using 128 GPUs with a total of 30,720 processing elements. Our results demonstrate that multi-GPU clusters can substantially accelerate computational fluid dynamics (CFD) simulations

A Full-Depth Amalgamated Parallel 3D Geometric Multigrid Solver for GPU Clusters

Numerical computations of incompressible flow equations with pressure-based algorithms necessitate the solution of an elliptic Poisson equation, for which multigrid methods are known to be very efficient. In our previous work we presented a dual-level (MPI-CUDA) parallel implementation of the Navier-Stokes equations to simulate buoyancy-driven incompressible fluid flows on GPU clusters with simple iterative methods while focusing on the scalability of the overall solver. In the present study we describe the implementation and performance of a multigrid method to solve the pressure Poisson equation within our MPI-CUDA parallel incompressible flow solver. Various design decisions and algorithmic choices for multigrid methods are explored in light of NVIDIA’s recent Fermi architecture. We discuss how unique aspects of an MPI-CUDA implementation for GPU clusters is related to the software choices made to implement the multigrid method. We propose a new coarse grid solution method of embedded multigrid with amalgamation and show that the parallel implementation retains the numerical efficiency of the multigrid method. Performance measurements on the NCSA Lincoln and TACC Longhorn clusters are presented for up to 64 GPUs

Scalability of Incompressible Flow Computations on Multi-GPU Clusters Using Dual-Level and Tri-Level Parallelism

High performance computing using graphics processing units (GPUs) is gaining popularity in the scientific computing field, with many large compute clusters being augmented with multiple GPUs in each node. We investigate hybrid tri-level (MPI-OpenMP-CUDA) parallel implementations to explore the efficiency and scalability of incompressible flow computations on GPU clusters up to 128 GPUS. This work details some of the unique issues faced when merging fine-grain parallelism on the GPU using CUDA with coarse-grain parallelism using OpenMP for intra-node and MPI for inter-node communication. Comparisons between the tri-level MPI-OpenMP-CUDA and dual-level MPI-CUDA implementations are shown using computationally large computational fluid dynamics (CFD) simulations. Our results demonstrate that a tri-level parallel implementation does not provide a significant advantage in performance over the dual-level implementation, however further research is needed to justify our conclusion for a cluster with a high GPU per node density or when using software that can utilize OpenMP’s fine-grain parallelism more effectively

A Century of Scholarly Neglect: Shakespeare and Greek Drama

In the late 19th and early 20th centuries, a number of Shakespeare scholars, including Israel Gollancz (1894), H.R.D. Anders (1904), J. Churton Collins (1904), and Gilbert Murray (1914) wrote convincingly of Shakespeare’s debt to classical Greek drama. However, in the century since, most scholars and editors have repeatedly held that Shakespeare was not familiar with Greek drama. In Classical Mythology in Shakespeare (1903), Robert Kilburn Root expressed the opinion on Shakespeare’s ‘lesse Greek’ that presaged this enduring dismissal: “It is at any rate certain that he nowhere alludes to any characters or episodes of Greek drama, that they extended no influence whatsoever on his conception of mythology.” (p. 6)   This century-long consensus against Attic dramatic influence was reinforced by A.D. Nutall, who wrote, “that Shakespeare was cut off from Greek poetry and drama is probably a bleak truth that we should accept.” (Nutall, 2004, p.210) Scholars have preferred to maintain that Plutarch or Ovid were Shakespeare’s surrogate literary mediators for the playwright’s adaptations from Greek myth and theatre. Other scholars, however, have questioned these assumptions, including Laurie Maguire, who observed that “invoking Shakespeare’s imagined conversations in the Mermaid tavern is not a methodology likely to convince skeptics that Shakespeare knew Greek drama.” (p. 98) This near-universal rejection of Greek drama as Shakespeare sources have profound philological implications. Indeed, this essay argues that the proscription against recognizing the Attic canon as an influence in Shakespeare has been driven by the belief that Will Shakspere of Stratford had, at most, an education that was Latin-based. The examples show that the real author had to have been exposed to both the Greek language and the Greek dramatists. Evidence for alternative candidates, including Edward de Vere, shows that many were schooled in Greek and that some even collected and supported translations of Greek works. It is my contention that Shakespeare’s dramatic imagination was actually fired by the Greeks, and Shakespeare research has clearly suffered from a century of denial

Horace and his influence.

Our debt to Greece and Rome.LEIDSSTELSELOPLADEN-RUG0