GPU accelerated maximum cardinality matching algorithms for bipartite graphs

We design, implement, and evaluate GPU-based algorithms for the maximum cardinality matching problem in bipartite graphs. Such algorithms have a variety of applications in computer science, scientific computing, bioinformatics, and other areas. To the best of our knowledge, ours is the first study which focuses on GPU implementation of the maximum cardinality matching algorithms. We compare the proposed algorithms with serial and multicore implementations from the literature on a large set of real-life problems where in majority of the cases one of our GPU-accelerated algorithms is demonstrated to be faster than both the sequential and multicore implementations.Comment: 14 pages, 5 figure

Revisiting hypergraph models for sparse matrix partitioning

hypergraph models for sparse matrix decomposition b

Hypergraph partitioning for multiple communication cost metrics: Model and methods

International audienceWe investigate hypergraph partitioning-based methods for efficient paralleliza-tion of communicating tasks. A good partitioning method should divide the load among the processors as evenly as possible and minimize the inter-processor communication overhead. The total communication volume is the most popular communication overhead metric which is reduced by the existing state-of-the-art hypergraph partitioners. However, other metrics such as the total number of messages, the maximum amount of data transferred by a processor, or a combination of them are equally, if not more, important. Existing hypergraph-based solutions use a two phase approach to minimize such metrics where in each phase, they minimize a different metric, sometimes at the expense of others. We propose a one-phase approach where all the communication cost metrics can be effectively minimized in a multi-objective setting and reductions can be achieved for all metrics together. For an accurate modeling of the maximum volume and the number of messages sent and received by a processor, we propose the use of directed hypergraphs. The directions on hyperedges necessitate revisiting the standard partitioning heuristics. We do so and propose a multi-objective, multi-level hypergraph partitioner called UMPa. The partitioner takes various prioritized communication metrics into account, and optimizes all of them together in the same phase. Compared to the state-of-the-art methods which only minimize the total communication volume, we show on a large number of problem instances that UMPa produces better partitions in terms of several communication metrics

Fast and high quality topology-aware task mapping

International audienceConsidering the large number of processors and the size of the interconnection networks on exascale-capable supercomputers, mapping concurrently executable and communicating tasks of an application is a complex problem that needs to be dealt with care. For parallel applications, the communication overhead can be a significant bottleneck on scalability. Topology-aware task-mapping methods that map the tasks to the processors (i.e., cores) by exploiting the underlying network information are very effective to avoid, or at worst bend, this limitation. We propose novel, efficient, and effective task mapping algorithms employing a graph model. The experiments show that the methods are faster than the existing approaches proposed for the same task, and on 4096 processors, the algorithms improve the communication hops and link contentions by 16% and 32%, respectively, on the average. In addition, they improve the average execution time of a parallel SpMV kernel and a communication-only application by 9% and 14%, respectively

Load-Balanced Local Time Stepping for Large-Scale Wave Propagation

In complex acoustic or elastic media, finite element meshes often require regions of refinement to honour external or internal topography, or small-scale features. These localized smaller elements create a bottleneck for explicit time-stepping schemes due to the Courant-Friedrichs-Lewy stability condition. Recently developed local time stepping (LTS) algorithms reduce the impact of these small elements by locally adapting the time-step size to the size of the element. The recursive, multi-level nature of our LTS scheme introduces an additional challenge, as standard partitioning schemes create a strong load imbalance across processors. We examine the use of multi-constraint graph and hypergraph partitioning tools to achieve effective, load-balanced parallelization. We implement LTS-Newmark in the seismology code SPECFEM3D and compare performance and scalability between different partitioning tools on CPU and GPU clusters using examples from computational seismology

Protective Role Of Intracoronary Shunt In Off-Pump Coronary Bypass Operations

Objective: To investigate if there are any advantages in using intracoronary shunts compared to shuntless operations, in the context of whether it has a protective role for the myocardia. Methods: This prospective study, included 100 patients who underwent off-pump coronary bypass surgery at 2 different cardiovascular surgery departments, namely, the Social Security Ankara Ihtisas Hospital, and Hacettepe University Hospital, Turkey, between September 2002 and July 2006. Patients were divided into 2 groups. In group 1 (n=50) off-pump coronary bypass operations were performed with intracoronary shunts. In group 2 (n=50) shunts were not used during off-pump. Serum creatine kinase, myoglobin, and troponin were studied. Results: There were significant increases in serum creatine kinase levels in group 2 at postoperative 6th, 12th, and 24th hours. In group 2, the increase of myoglobin was statistically significant at only the postoperative 24th hour. Troponin levels were significantly higher in group 2 at postoperative 6th, 12th, and 24th hours. Conclusion: There are some questions regarding myocardial protection while maintaining a bloodless secure surgical field in off-pump coronary surgery. However, use of intracoronary shunts provides distal coronary flow, and reduces the risk of myocardial ischemia, while maintaining a comfortable blood free anastomosis area.Wo