BDDT: Block-Level Dynamic Dependence Analysis for Task-Based Parallelism

Abstract

Abstract. We present BDDT, a task-parallel runtime system that dynamically discovers and resolves dependencies among parallel tasks. BDDT allows the programmer to specify detailed task footprints on any memory address range, multidimensional array tile or dynamic region. BDDT uses a block-based dependence analysis with arbitrary granularity. The analysis is applicable to existing C programs without having to restructure object or array allocation, and provides flexibility in array layouts and tile dimensions. We evaluate BDDT using a representative set of benchmarks, and we compare it to SMPSs (the equivalent runtime system in StarSs) and OpenMP. BDDT performs comparable to or better than SMPSs and is able to cope with task granularity as much as one order of magnitude finer than SMPSs. Compared to OpenMP, BDDT performs up to 3.9× better for benchmarks that benefit from dynamic dependence analysis. BDDT provides additional data annotations to bypass dependence analysis. Using these annotations, BDDT outperforms OpenMP also in benchmarks where dependence analysis does not discover additional parallelism, thanks to a more efficient implementation of the runtime system.

A Runtime Heuristic to Selectively Replicate Tasks for Application-Specific Reliability Targets

“…Meanwhile even though the performance and efficiency advantages of task-based dataflow programming models [19] and runtimes [41] are well-established, to the best of our knowledge, there has been no research investigating selective replication in these programming models. As consequence, we strive to leverage the resilience advantages of such frameworks to develop fully automatic runtime selective task replication heuristics.…”

TProf: An energy profiler for task-parallel programs

“…We design and implement TProf, an energy profiler for the BDDT runtime, which implements OpenMP tasks [42]. 2.…”

“…As a baseline task runtime we use BDDT (Block-Level Dynamic Dependence Analysis for Task-Based Parallelism) which provides the mechanisms for task issuing, instantiation and completio [42]. BDDT uses an OMP-like task syntax and it was preferred over other alternatives such as openMP or ompSS due to the authors' familiarity with it.…”

“…The difficulty in writing multithreaded parallel programs has lead to the development of higher-level abstractions for parallel programming, such as task-parallel languages [6,21,13,3], domainspecific parallel languages, pattern libraries that hide lowlevel threads from the programmer [33] and task-parallel programming models [7,31,2,42,42]. Compared to the traditional thread programming, task-parallel programs are easier to write, more portable, and scale better, because the parallelism is not hard-wired into the program, but created at runtime, as needed.…”

Online Dynamic Dependence Analysis for Speculative Polyhedral Parallelization

“…It is specifically designed for the future language constructor, managing the results of asynchronous computations. Other approaches concern dependence analysis between parallel tasks and rely on code annotations that specify the memory footprint of each task [13]. Using the programmer's annotations, the profiler may be disabled to reduce the overhead for embarrassingly parallel codes.…”