An algorithm for unsteady viscous flows at all speeds

An algorithm for the simulation of unsteady, viscous, stratified compressible flows, which remains valid at all speeds, is presented. The method is second-order accurate in both space and time and is independent of the Mach number. In order to remove the stiffness of the numerical problem due to the large disparity between the flow speed and the acoustic wave speed at low Mach number, an approximate Newton method, based on artificial compressibility, is proposed. Additionally, a modified advection upstream splitting method (AUSM +) scheme is used, which permits accurate computations of both compressible and incompressible flows. A detailed description of the method and an efficiency comparison with other approximate Newton methods described in the literature are given. Furthermore, it is shown that the accuracy of the algorithm is not dependent on the Mach number through the computations of various benchmark test cases. Copyright (C) 2000 John Wiley & Sons, Ltd

OpenMP Loop Scheduling Revisited: Making a Case for More Schedules

In light of continued advances in loop scheduling, this work revisits the OpenMP loop scheduling by outlining the current state of the art in loop scheduling and presenting evidence that the existing OpenMP schedules are insufficient for all combinations of applications, systems, and their characteristics. A review of the state of the art shows that due to the specifics of the parallel applications, the variety of computing platforms, and the numerous performance degradation factors, no single loop scheduling technique can be a 'one-fits-all' solution to effectively optimize the performance of all parallel applications in all situations. The impact of irregularity in computational workloads and hardware systems, including operating system noise, on the performance of parallel applications, results in performance loss and has often been neglected in loop scheduling research, in particular, the context of OpenMP schedules. Existing dynamic loop self-scheduling techniques, such as trapezoid self-scheduling, factoring, and weighted factoring, offer an unexplored potential to alleviate this degradation in OpenMP due to the fact that they explicitly target the minimization of load imbalance and scheduling overhead. Through theoretical and experimental evaluation, this work shows that these loop self-scheduling methods provide a benefit in the context of OpenMP. In conclusion, OpenMP must include more schedules to offer a broader performance coverage of applications executing on an increasing variety of heterogeneous shared memory computing platforms

Saperlipopette!: a Distributed Web Caching Systems Evaluation Tool

Designing a distributed cache infrastructure to improve the Web performance for the users of a large-scale organization is a difficult task. To guide the decisions of system administrators, we propose Saperlipopette!, a tool that can be used to evaluate, a-priori, the quality of the service offered by each potential configuration of the distributed cache infrastructure. Saperlipopette! is based on trace-driven simulations. Our methodology is two-fold. First, we monitor the targeted organizations' Web related activity. Second, we replay the organization's access pattern while simulating the distributed Web support infrastructure. This paper presents the information gathering as well as the design of the tool. We show that beyond a certain cache's size, the performance stays constant whereas the consistency continues to decrease. We also evaluated a number of distributed configurations, among which peer-to-peer Relais cooperation proved to be the best one. Keywords Web caches, configur..