A dynamic scheduling method for irregular parallel programs

Abstract-In this work, we address the problem of scheduling loops with dependences in the context of speculative parallelization. We show that the scheduling alternatives are highly influenced by the dependence violation pattern the code presents. We center our analysis in those algorithms where dependences are less likely to appear as the execution proceeds. Particularly, we focus on randomized incremental algorithms, widely used as a much more efficient solution to many problems than their deterministic counterparts. These important algorithms are, in general, hard to parallelize by hand and represent a challenge for any automatic parallelization scheme. Our analysis led us to the development of MESETA, a new scheduling strategy that takes into account the probability of a dependence violation to determine the number of iterations being scheduled. MESETA is compared with existing techniques, including Fixed-Size Chunking (FSC), the only scheduling alternative used so far in the context of speculative parallelization. Our experimental results show a 5.5 percent to 36.25 percent speedup improvement over FSC, leading to a better extraction of the parallelism inherent to randomized incremental algorithms. Moreover, when the cost of dependence violations is too high to obtain speedups, MESETA curves the performance degradation.Index Terms-Parallelism and concurrency, load balancing and task assignment, scheduling and task partitioning, geometrical problems and computations.

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“…We do not consider adaptive scheduling policies in this work, such as the Tapering algorithm by Lucco [23].…”

Section: Review Of Scheduling Alternatives For Parallel Loopsmentioning

confidence: 99%

New Scheduling Strategies for Randomized Incremental Algorithms in the Context of Speculative Parallelization

Llanos

Orden

Palop

2007

IEEE Trans. Comput.

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“…Other schedules, similar in nature to GUIDED, have been proposed in the literature, such as trapezoid scheduling [1], factoring [2], and tapering [3]. These schedules are variations of the previous ones and are tailored for certain load unbalance patterns.…”

Section: Motivation and Related Workmentioning

confidence: 99%

Is the Schedule Clause Really Necessary in OpenMP?

Ayguadé

Blainey

Durán

et al. 2003

OpenMP Shared Memory Parallel Programming

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Abstract.Choosing the appropriate assignment of loop iterations to threads is one of the most important decisions that need to be taken when parallelizing Loops, the main source of parallelism in numerical applications. This is not an easy task, even for expert programmers, and it can potentially take a large amount of time. OpenMP offers the schedule clause, with a set of predefined iteration scheduling strategies, to specify how (and when) this assignment of iterations to threads is done. In some cases, the best schedule depends on architectural characteristics of the target architecture, data input, ... making the code less portable. Even worse, the best schedule can change along execution time depending on dynamic changes in the behavior of the loop or changes in the resources available in the system. Also, for certain types of imbalanced loops, the schedulers already proposed in the literature are not able to extract the maximum parallelism because they do not appropriately trade-off load balancing and data locality. This paper proposes a new scheduling strategy, that derives at run time the best scheduling policy for each parallel loop in the program, based on information gathered at runtime by the library itself.

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“…We do not consider adaptive scheduling policies in this work, such as the Tapering algorithm by Lucco [11].…”

Section: Trapezoidal Scheduling (Tss)mentioning

confidence: 99%

MESETA: A New Scheduling Strategy for Speculative Parallelization of Randomized Incremental Algorithms

Llanos

Orden

Palop

2005 International Conference on Parallel Processing Workshops (ICPPW'05)

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A dynamic scheduling method for irregular parallel programs

Cited by 60 publications

References 26 publications

New Scheduling Strategies for Randomized Incremental Algorithms in the Context of Speculative Parallelization

New Scheduling Strategies for Randomized Incremental Algorithms in the Context of Speculative Parallelization

Is the Schedule Clause Really Necessary in OpenMP?

MESETA: A New Scheduling Strategy for Speculative Parallelization of Randomized Incremental Algorithms

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