TechTalks from event: IEEE IPDPS 2011

Note 1: Only plenary sessions (keynotes, panels, and best papers) are accessible without requiring log-in. For other talks, you will need to log-in using the email you registered for IPDPS 2011. Note 2: Many of the talks (those without a thumbnail next to the their description below) are yet to be uploaded. Some of them were not recorded because of technical problems. We are working with the corresponding authors to upload the self-recorded versions here. We sincerely thank all authors for their efforts in making their videos available.

SESSION 17: Parallel Algorithms

  • A New Data Layout For Set Intersection on GPUs Authors: Rasmus Amossen (IT University of Copenhagen, Denmark); Rasmus Pagh (University of Copenhagen, Denmark)
    Set intersection is the core in a variety of problems, e.g. frequent itemset mining and sparse boolean matrix multiplication. It is well-known that large speed gains can, for some computational problems, be obtained by using a graphics processing unit (GPU) as a massively parallel computing device. However, GPUs require highly regular control ?ow and memory access patterns, and for this reason previous GPU methods for intersecting sets have used a simple bitmap representation. This representation requires excessive space on sparse data sets. In this paper we present a novel data layout, ”BatMap”, that is particularly well suited for parallel processing, and is compact even for sparse data. Frequent itemset mining is one of the most important applications of set intersection. As a case-study on the potential of BatMaps we focus on frequent pair mining, which is a core special case of frequent itemset mining. The main ?nding is that our method is able to achieve speedups over both Apriori and FP-growth when the number of distinct items is large, and the density of the problem instance is above 0.01. Previous implementations of frequent itemset mining on GPU have not been able to show speedups over the best single-threaded implementations.
  • Partitioning Spatially Located Computations using Rectangles Authors: Erik Saule (The Ohio State University, USA); Erdeniz O. Bas (The Ohio State University, USA); Umit V. Catalyurek (The Ohio Stat
    The ideal distribution of spatially located heterogeneous workloads is an important problem to address in parallel scienti?c computing. We investigate the problem of partitioning such workloads (represented as a matrix of positive integers) into rectangles, such that the load of the most loaded rectangle (processor) is minimized. Since ?nding the optimal arbitrary rectangle-based partition is an NP-hard problem, we investigate particular classes of solutions, namely, rectilinear partitions, jagged partitions and hierarchical partitions. We present a new class of solutions called m-way jagged partitions, propose new optimal algorithms for m-way jagged partitions and hierarchical partitions, propose new heuristic algorithms, and provide worst case performance analyses for some existing and new heuristics. Moreover, the algorithms are tested in simulation on a wide set of instances. Results show that two of the algorithms we introduce lead to a much better load balance than the state-of-the-art algorithms.
  • Reduced-Bandwidth Multithreaded Algorithms for Sparse-Matrix Vector Multiplication Authors: Aydin Buluc (Lawrence Berkeley National Laboratory, USA); Samuel W. Williams (Lawrence Berkeley National Laboratory, USA); Leon
    On multicore architectures, the ratio of peak memory bandwidth to peak ?oating-point performance (byte:?op ratio) is decreasing as core counts increase, further limiting the performance of bandwidth limited applications. Multiplying a sparse matrix (as well as its transpose in the unsymmetric case) with a dense vector is the core of sparse iterative methods. In this paper, we present a new multithreaded algorithm for the symmetric case which potentially cuts the bandwidth requirements in half while exposing lots of parallelism in practice. We also give a new data structure transformation, called bitmasked register blocks, which promises signi?cant reductions on bandwidth requirements by reducing the number of indexing elements without introducing additional ?ll-in zeros. Our work shows how to incorporate this transformation into existing parallel algorithms (both symmetric and unsymmetric) without limiting their parallel scalability. Experimental results indicate that the combined bene?ts of bitmasked register blocks and the new symmetric algorithm can be as high as a factor of 3.5x in multicore performance over an already scalable parallel approach. We also provide a model that accurately predicts the performance of the new methods, showing that even larger performance gains are expected in future multicore systems as current trends (decreasing byte:?op ratio and larger sparse matrices) continue.