Harshvardhan,; Amato, Nancy M.; Rauchwerger, Lawrence(Proceedings of the 20th ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming - PPoPP 2015, Association for Computing Machinery (ACM), 2015)[Conference Paper]
Large-scale graph computing has become critical due to the ever-increasing size of data. However, distributed graph computations are limited in their scalability and performance due to the heavy communication inherent in such computations. This is exacerbated in scale-free networks, such as social and web graphs, which contain hub vertices that have large degrees and therefore send a large number of messages over the network. Furthermore, many graph algorithms and computations send the same data to each of the neighbors of a vertex. Our proposed approach recognizes this, and reduces communication performed by the algorithm without change to user-code, through a hierarchical machine model imposed upon the input graph. The hierarchical model takes advantage of locale information of the neighboring vertices to reduce communication, both in message volume and total number of bytes sent. It is also able to better exploit the machine hierarchy to further reduce the communication costs, by aggregating traffic between different levels of the machine hierarchy. Results of an implementation in the STAPL GL shows improved scalability and performance over the traditional level-synchronous approach, with 2.5 × - 8× improvement for a variety of graph algorithms at 12, 000+ cores.
Papadopoulos, Ioannis; Thomas, Nathan; Fidel, Adam; Amato, Nancy M.; Rauchwerger, Lawrence(Proceedings of the 29th ACM on International Conference on Supercomputing - ICS '15, Association for Computing Machinery (ACM), 2015)[Conference Paper]
Fidel, Adam; Amato, Nancy M.; Rauchwerger, Lawrence(Proceedings of the 23rd international conference on Parallel architectures and compilation - PACT '14, Association for Computing Machinery (ACM), 2014)[Conference Paper]
Lindsey, Aaron; Yeh, Hsin-Yi (Cindy); Wu, Chih-Peng; Thomas, Shawna; Amato, Nancy M.(Proceedings of the 5th ACM Conference on Bioinformatics, Computational Biology, and Health Informatics - BCB '14, Association for Computing Machinery (ACM), 2014)[Conference Paper]
Tomkins, Daniel; Smith, Timmie; Amato, Nancy M.; Rauchwerger, Lawrence(Proceedings of the 19th ACM SIGPLAN symposium on Principles and practice of parallel programming - PPoPP '14, Association for Computing Machinery (ACM), 2014)[Conference Paper]
Tarjan's famous linear time, sequential algorithm for finding the strongly connected components (SCCs) of a graph relies on depth first search, which is inherently sequential. Deterministic parallel algorithms solve this problem in logarithmic time using matrix multiplication techniques, but matrix multiplication requires a large amount of total work. Randomized algorithms based on reachability - the ability to get from one vertex to another along a directed path - greatly improve the work bound in the average case. However, these algorithms do not always perform well; for instance, Divide-and-Conquer Strong Components (DCSC), a scalable, divide-and-conquer algorithm, has good expected theoretical limits, but can perform very poorly on graphs for which the maximum reachability of any vertex is small. A related algorithm, MultiPivot, gives very high probability guarantees on the total amount of work for all graphs, but this improvement introduces an overhead that increases the average running time. This work introduces SCCMulti, a multi-pivot improvement of DCSC that offers the same consistency as MultiPivot without the time overhead. We provide experimental results demonstrating SCCMulti's scalability; these results also show that SCCMulti is more consistent than DCSC and is always faster than MultiPivot.
Hong, Sungpack; Salihoglu, Semih; Widom, Jennifer; Olukotun, Kunle(Proceedings of Annual IEEE/ACM International Symposium on Code Generation and Optimization - CGO '14, Association for Computing Machinery (ACM), 2014)[Conference Paper]
Large-scale graph processing, with its massive data sets, requires distributed processing. However, conventional frameworks for distributed graph processing, such as Pregel, use non-traditional programming models that are well-suited for parallelism and scalability but inconvenient for implementing non-trivial graph algorithms. In this paper, we use Green-Marl, a Domain-Specific Language for graph analysis, to intuitively describe graph algorithms and extend its compiler to generate equivalent Pregel implementations. Using the semantic information captured by Green-Marl, the compiler applies a set of transformation rules that convert imperative graph algorithms into Pregel's programming model. Our experiments show that the Pregel programs generated by the Green-Marl compiler perform similarly to manually coded Pregel implementations of the same algorithms. The compiler is even able to generate a Pregel implementation of a complicated graph algorithm for which a manual Pregel implementation is very challenging.
Nath, Shuvra Kanti; Thomas, Shawna; Ekenna, Chinwe; Amato, Nancy M.(Proceedings of the ACM Conference on Bioinformatics, Computational Biology and Biomedicine - BCB '12, Association for Computing Machinery (ACM), 2012)[Conference Paper]
Oancea, Cosmin E.; Rauchwerger, Lawrence(Proceedings of the 33rd ACM SIGPLAN conference on Programming Language Design and Implementation - PLDI '12, Association for Computing Machinery (ACM), 2012)[Conference Paper]
Benzina, Amal; Dey, Arindam; Toennis, Marcus; Klinker, Gudrun(Proceedings of the 10th asia pacific conference on Computer human interaction - APCHI '12, Association for Computing Machinery (ACM), 2012)[Conference Paper]
Mobile phones provide an interesting all-in-one alternative for 3D input devices in virtual environments. Mobile phones are becoming touch sensitive and spatially aware, and they are now part of our daily activities. We present Phone-Based Motion Control, a novel one-handed travel technique for a virtual environment. The technique benefits from the touch capability offered by growing number of mobile phones to change viewpoint translation in virtual environments, while the orientation of the viewpoint is controlled by built-in sensors in the mobile phone. The travel interaction separates translation (touch based translation control) and rotation (steer based rotation control), putting each set of degrees of freedom (DOF) to a separate interaction technique (separability). This paper examines, how many DOF are needed to perform the travel task as easy and comfortable as possible. It also investigates different mapping functions between the user's actions on the mobile phone and the viewpoint change in the virtual environment. Therefore, four techniques are implemented: rotate by heading, rotate by roll, rotate by roll with fixed horizon and a merged rotation. Each technique has either 4 or 5 DOF and different mappings between phone and viewpoint coordinates in the virtual environment. We perform an extensive user study to explore different aspects related to the travel techniques in terms of DOF and mapping functions. Results of the user evaluation show that 4 DOF techniques seem to perform better the travel task. Even though, the results were not statistically decisive in favor of the usage of the mobile roll to control the viewpoint heading in the virtual environment despite the good results, there is a clear tendency from the users to prefer the mobile roll as the desired mapping. Copyright 2012 ACM.
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