| 1. |
- Benkner, Siegfried, et al.
(author)
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PEPPHER : Efficient and Productive Usage of Hybrid Computing Systems
- 2011
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In: IEEE Micro. - : IEEE Institute of Electrical and Electronics. - 0272-1732 .- 1937-4143. ; 31:5, s. 28-41
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Journal article (peer-reviewed)abstract
- PEPPHER, a three-year European FP7 project, addresses efficient utilization of hybrid (heterogeneous) computer systems consisting of multicore CPUs with GPU-type accelerators. This article outlines the PEPPHER performance-aware component model, performance prediction means, runtime system, and other aspects of the project. A larger example demonstrates performance portability with the PEPPHER approach across hybrid systems with one to four GPUs.
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| 2. |
- Markidis, Stefano, et al.
(author)
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The EPiGRAM Project : Preparing Parallel Programming Models for Exascale
- 2016
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In: HIGH PERFORMANCE COMPUTING, ISC HIGH PERFORMANCE 2016 INTERNATIONAL WORKSHOPS. - Cham : Springer. - 9783319460796 - 9783319460789 ; , s. 56-68
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Conference paper (peer-reviewed)abstract
- EPiGRAM is a European Commission funded project to improve existing parallel programming models to run efficiently large scale applications on exascale supercomputers. The EPiGRAM project focuses on the two current dominant petascale programming models, message-passing and PGAS, and on the improvement of two of their associated programming systems, MPI and GASPI. In EPiGRAM, we work on two major aspects of programming systems. First, we improve the performance of communication operations by decreasing the memory consumption, improving collective operations and introducing emerging computing models. Second, we enhance the interoperability of message-passing and PGAS by integrating them in one PGAS-based MPI implementation, called EMPI4Re, implementing MPI endpoints and improving GASPI interoperability with MPI. The new EPiGRAM concepts are tested in two large-scale applications, iPIC3D, a Particle-in-Cell code for space physics simulations, and Nek5000, a Computational Fluid Dynamics code.
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| 3. |
- Wimmer, Martin, et al.
(author)
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Configurable Strategies for Work-stealing
- 2013
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Reports (other academic/artistic)abstract
- Work-stealing systems are typically oblivious to the nature of the tasks theyare scheduling. For instance, they do not know or take into account how long atask will take to execute or how many subtasks it will spawn. Moreover, theactual task execution order is typically determined by the underlying taskstorage data structure, and cannot be changed. There are thus possibilities foroptimizing task parallel executions by providing information on specific tasksand their preferred execution order to the scheduling system. We introduce scheduling strategies to enable applications to dynamicallyprovide hints to the task-scheduling system on the nature of specific tasks.Scheduling strategies can be used to independently control both local taskexecution order as well as steal order. In contrast to conventional schedulingpolicies that are normally global in scope, strategies allow the scheduler toapply optimizations on individual tasks. This flexibility greatly improvescomposability as it allows the scheduler to apply different, specificscheduling choices for different parts of applications simultaneously. Wepresent a number of benchmarks that highlight diverse, beneficial effects thatcan be achieved with scheduling strategies. Some benchmarks (branch-and-bound,single-source shortest path) show that prioritization of tasks can reduce thetotal amount of work compared to standard work-stealing execution order. Forother benchmarks (triangle strip generation) qualitatively better results canbe achieved in shorter time. Other optimizations, such as dynamic merging oftasks or stealing of half the work, instead of half the tasks, are also shownto improve performance. Composability is demonstrated by examples that combinedifferent strategies, both within the same kernel (prefix sum) as well as whenscheduling multiple kernels (prefix sum and unbalanced tree search).
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| 4. |
- Wimmer, Martin, et al.
(author)
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Data structures for task-based priority scheduling
- 2014
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In: ACM SIGPLAN Notices. - : Association for Computing Machinery (ACM). - 1523-2867 .- 0362-1340 .- 1558-1160. ; 49:8, s. 379-380
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Journal article (peer-reviewed)abstract
- We present three lock-free data structures for priority task scheduling: a priority work-stealing one, a centralized one with ρ-relaxed semantics, and a hybrid one combining both concepts. With the single-source shortest path (SSSP) problem as example, we show how the different approaches affect the prioritization and provide upper bounds on the number of examined nodes. We argue that priority task scheduling allows for an intuitive and easy way to parallelize the SSSP problem, notoriously a hard task. Experimental evidence supports the good scalability of the resulting algorithm. The larger aim of this work is to understand the trade-offs between scalability and priority guarantees in task scheduling systems. We show that ρ-relaxation is a valuable technique for improving the first, while still allowing semantic constraints to be satisfied: the lock-free, hybrid $k$-priority data structure can scale as well as work-stealing, while still providing strong priority scheduling guarantees, which depend on the parameter k. Our theoretical results open up possibilities for even more scalable data structures by adopting a weaker form of ρ-relaxation, which still enables the semantic constraints to be respected.
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