A Toolchain to Verify the Parallelization of OmpSs-2 Applications

Economo, Simone; Royuela, Sara; Ayguadé, Eduard; Beltrán, Vicenç

doi:10.1007/978-3-030-57675-2_2

Cited by 3 publications

(2 citation statements)

References 14 publications

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“…Generally, tracking usages of the induction variable in a loop is a straightforward way to determine if the task DAG changes, and does not require a full analysis of the target application. Moreover, this proposal could be combined with existing static and dynamic analysis tools [32] to facilitate the usage of the taskiter construct.…”

Section: #Pragma Oss Taskiter [Clause []] New-line Loopmentioning

confidence: 99%

Optimizing Iterative Data-flow Scientific Applications using Directed Cyclic Graphs

Álvarez

Beltrán

2023

IEEE Access

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Data-flow programming models have become a popular choice for writing parallel applications as an alternative to traditional work-sharing parallelism. They are better suited to write applications with irregular parallelism that can present load imbalance. However, these programming models suffer from overheads related to task creation, scheduling and dependency management, limiting performance and scalability when tasks become too small. At the same time, many HPC applications implement iterative methods or multi-step simulations that create the same directed acyclic graphs of tasks on each iteration. By giving application programmers a way to express that a specific loop is creating the same task pattern on each iteration, we can create a single task DAG once and transform it into a cyclic graph. This cyclic graph is then reused for successive iterations, minimizing task creation and dependency management overhead. This paper presents the taskiter, a new construct we propose for the OmpSs-2 and OpenMP programming models, allowing the use of directed cyclic task graphs (DCTG) to minimize runtime overheads. Moreover, we present a simple immediate successor locality-aware heuristic that minimizes task scheduling overhead by bypassing the runtime task scheduler. We evaluate the implementation of the taskiter and the immediate successor heuristic in 8 iterative benchmarks. Using small task granularities, we obtain a geometric mean speedup of 2.56x over the reference OmpSs-2 implementation, and a 3.77x and 5.2x speedup over the LLVM and GCC OpenMP runtimes, respectively.INDEX TERMS taskiter, data-flow programming, ompss-2, openmp, iterative applications

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Section: #Pragma Oss Taskiter [Clause []] New-line Loopmentioning

confidence: 99%

Optimizing Iterative Data-flow Scientific Applications using Directed Cyclic Graphs

Álvarez

Beltrán

2023

IEEE Access

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“…Automatic finding/verification of accesses: Tareador [30] uses an LLVM compiler stage to instrument all read-write instructions in a sequential application. This instrumentation [32] is a run-time dynamic binary instrumentation tool that addresses the same problem. These tools all introduce enormous performance overhead of at least an order of magnitude.…”

Section: Related Workmentioning

confidence: 99%

Automatic aggregation of subtask accesses for nested OpenMP-style tasks

Shaaban

Aguilar

Beltrán

et al. 2022

2022 IEEE 34th International Symposium on Computer Architecture and High Performance Computing (SBAC-PAD)

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Task-based programming is a high performance and productive model to express parallelism. Tasks encapsulate work to be executed across multiple cores or offloaded to GPUs, FPGAs, other accelerators or other nodes. In order to maintain parallelism and afford maximum freedom to the scheduler, the task dependency graph should be created in parallel and well in advance of task execution. A key limitation with OpenMP and OmpSs-2 tasking is that a task cannot be created until all its accesses and its descendents' accesses are known. Current approaches to work around this limitation either stop task creation and execution using a taskwait or they substitute "fake" accesses known as sentinels. This paper proposes the auto clause, which indicates that the task may create subtasks that access unspecified memory regions or it may allocate and return memory at addresses that are of course not yet known. Unlike approaches using taskwaits, there is no interruption to the concurrent creation and execution of tasks, maintaining parallelism and the scheduler's ability to optimize load balance and data locality. Unlike existing approaches using sentinels, all tasks can be given a precise specification of their own data accesses, so that a single mechanism is used to control task ordering, program data transfers on distributed memory and optimize data locality, e.g. on NUMA systems. The auto clause also provides an incremental path to develop programs with nested tasks, by removing the need for every parent task to have a complete specification of the accesses of its descendent tasks. This is redundant information that can be time consuming and error-prone to describe. We present a straightforward runtime implementation that achieves a 1.4 times speedup for n-body with OmpSs-2@Cluster task offloading to 32 nodes and <4% slowdown for three benchmarks with task offloading to 8 nodes. All code is open source.

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User-defined Tools for Characterizing Task-Parallel Applications and Predicting Load Imbalance

Chung

Kranzlmüller

2021

2021 15th International Conference on Advanced Computing and Applications (ACOMP)

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A Toolchain to Verify the Parallelization of OmpSs-2 Applications

Cited by 3 publications

References 14 publications

Optimizing Iterative Data-flow Scientific Applications using Directed Cyclic Graphs

Optimizing Iterative Data-flow Scientific Applications using Directed Cyclic Graphs

Automatic aggregation of subtask accesses for nested OpenMP-style tasks

User-defined Tools for Characterizing Task-Parallel Applications and Predicting Load Imbalance

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