In parallel computing, a valid graph coloring yields a lock-free processing of the colored tasks, data points, etc., without expensive synchronization mechanisms. However, coloring is not free and the overhead can be significant. In particular, for the bipartite-graph partial coloring (BGPC) and distance-2 graph coloring (D2GC) problems, which have various use-cases within the scientific computing and numerical optimization domains, the coloring overhead can be in the order of minutes with a single thread for many real-life graphs.In this work, we propose parallel algorithms for bipartitegraph partial coloring on shared-memory architectures. Compared to the existing shared-memory BGPC algorithms, the proposed ones employ greedier and more optimistic techniques that yield a better parallel coloring performance. In particular, on 16 cores, the proposed algorithms perform more than 4× faster than their counterparts in the ColPack library which is, to the best of our knowledge, the only publicly-available coloring library for multicore architectures. In addition to BGPC, the proposed techniques are employed to devise parallel distance-2 graph coloring algorithms and similar performance improvements have been observed. Finally, we propose two costless balancing heuristics for BGPC that can reduce the skewness and imbalance on the cardinality of color sets (almost) for free. The heuristics can also be used for the D2GC problem and in general, they will probably yield a better color-based parallelization performance especially on many-core architectures.

No abstract

Sketches are probabilistic data structures that can provide approximate results within mathematically proven error bounds while using orders of magnitude less memory than traditional approaches. They are tailored for streaming data analysis on architectures even with limited memory such as single-board computers that are widely exploited for IoT and edge computing. Since these devices o er multiple cores, with e cient parallel sketching schemes, they are able to manage high volumes of data streams. However, since their caches are relatively small, a careful parallelization is required. In this work, we focus on the frequency estimation problem and evaluate the performance of a high-end server, a 4-core Raspberry Pi and an 8-core Odroid. As a sketch, we employed the widely used Count-Min Sketch. To hash the stream in parallel and in a cache-friendly way, we applied a novel tabulation approach and rearranged the auxiliary tables into a single one. To parallelize the process with performance, we modi ed the work ow and applied a form of bu ering between hash computations and sketch updates. Today, many single-board computers have heterogeneous processors in which slow and fast cores are equipped together. To utilize all these cores to their full potential, we proposed a dynamic load-balancing mechanism which significantly increased the performance of frequency estimation.

No abstract

Software systems generally have a large number of configurable options interacting with each other. Such systems are more likely to be prone to errors, crashes, and faulty executions that are usually caused by option interactions. To avoid such errors, testing all possible configurations during the development phase is usually not feasible, since the number of all possible configurations is exponential in the order of number of options. A t-way covering array (CA) is a 2-dimensional combinatorial object that helps to efficiently cover all t-length option interactions of the system under test. Generating a CA with a small number of configurations is important to shorten the testing phase. However, the testing cost (e.g. the testing time) may differ from one configuration to another. Currently, most sequential tools can generate optimum CAs in terms of number of configurations, but they are not cost-aware, i.e., they cannot handle the varying costs of configurations. In this work, we implement a parallel, cost-aware CA-generation tool based on a sequential tool, Jenny, to generate lower-cost CAs faster. Experimental results show that our cost-aware CA construction approach can generate 32% and 21% lower cost CAs on average for t=2 and t=3, respectively, compared to state-of-the-art CA-generation tools. Moreover, the costawareness comes for free, i.e., we speed up our algorithm by leveraging parallel computation. The cost models and cost reduction techniques we propose could also be adapted for other existing CA generation tools.