P systems with minimal parallelism

A current research topic in membrane computing is to find more realistic P systems from a biological point of view, and one target in this respect is to relax the condition of using the rules in a maximally parallel way. We contribute in this paper to this issue by considering the minimal parallelism of using the rules: if at least a rule from a set of rules associated with a membrane or a region can be used, then at least one rule from that membrane or region must be used, without any other restriction (e.g., more rules can be used, but we do not care how many). Weak as it might look, this minimal parallelism still leads to universality. We first prove this for the case of symport/antiport rules. The result is obtained both for generating and accepting P systems, in the latter case also for systems working deterministically. Then, we consider P systems with active membranes, and again the usual results are obtained: universality and the possibility to solve NP-complete problems in polynomial time (by trading space for time).     

Nested parallelism for multi-core HPC systems using Java

Since its introduction in 1993, the Message Passing Interface (MPI) has become a de facto standard for writing High Performance Computing (HPC) applications on clusters and Massively Parallel Processors (MPPs). The recent emergence of multi-core processor systems presents a new challenge for established parallel programming paradigms, including those based on MPI. This paper presents a new Java messaging system called MPJ Express. Using this system, we exploit multiple levels of parallelism–messaging and threading–to improve application performance on multi-core processors. We refer to our approach as nested parallelism. This MPI-like Java library can support nested parallelism by using Java or Java OpenMP (JOMP) threads within an MPJ Express process. Practicality of this approach is assessed by porting to Java a massively parallel structure formation code from Cosmology called Gadget-2. We introduce nested parallelism in the Java version of the simulation code and report good speed-ups. To the best of our knowledge it is the first time this kind of hybrid parallelism is demonstrated in a high performance Java application.     

Indian parallelism on unary ol systems

In this paper we impose the Indian parallelism restriction on the unary developmental system, i. e. on UOL system. We observe that corresponding to any P_aUL language we can get a unary language of Restricted parallel content free language (RP_aCLUL).

Section 1 deals with definitions and Section 2 deals with some propoerties of P_aUL systems. In Section 3, we compare P_aUL language with unary languages of parallel content free grammars and also characterize some subfamilies of P_aUL languages. In the last section, we state a few hierarchial and closure properties.     

A scalable scheduling scheme for functional parallelism ondistributed memory multiprocessor systems

We attempt a new variant of the scheduling problem by investigating the scalability of the schedule length with the required number of processors, by performing scheduling partially at compile time and partially at run time. Assuming infinite number of processors, the compile time schedule is found using a new concept of the threshold of a task that quantifies a trade-off between the schedule-length and the degree of parallelism. The schedule is found to minimize either the schedule length or the number of required processors and it satisfies: A feasibility condition which guarantees that the schedule delay of a task from its earliest start time is below the threshold, and an optimality condition which uses a merit function to decide the best task-processor match for a set of tasks competing for a given processor. At run time, the tasks are merged producing a schedule for a smaller number of available processors. This allows the program to be scaled down to the processors actually available at run time. Usefulness of this scheduling heuristic has been demonstrated by incorporating the scheduler in the compiler backend for targeting Sisal (Streams and Iterations in a Single Assignment Language) on iPSC/860     

Reordering for parallelism

The proposed ordering scheme is the fusion of Jess and Kees method and the Minimum degree ordering, that operates on a non-chordal graph. The method produces a fill preserving ordering for all the test problems selected from the Boeing-Harwell Sparse matrix collection. The extent of parallelism extracted is nearly the same as that obtained by using Liu's tree rotation heuristic.     

Runtime scheduling of dynamic parallelism on accelerator-based multi-core systems

We explore runtime mechanisms and policies for scheduling dynamic multi-grain parallelism on heterogeneous multi-core processors. Heterogeneous multi-core processors integrate conventional cores that run legacy codes with specialized cores that serve as computational accelerators. The term multi-grain parallelism refers to the exposure of multiple dimensions of parallelism from within the runtime system, so as to best exploit a parallel architecture with heterogeneous computational capabilities between its cores and execution units. We investigate user-level schedulers that dynamically “rightsize” the dimensions and degrees of parallelism on the cell broadband engine. The schedulers address the problem of mapping application-specific concurrency to an architecture with multiple hardware layers of parallelism, without requiring programmer intervention or sophisticated compiler support. We evaluate recently introduced schedulers for event-driven execution and utilization-driven dynamic multi-grain parallelization on Cell. We also present a new scheduling scheme for dynamic multi-grain parallelism, S-MGPS, which uses sampling of dominant execution phases to converge to the optimal scheduling algorithm. We evaluate S-MGPS on an IBM Cell BladeCenter with two realistic bioinformatics applications that infer large phylogenies. S-MGPS performs within 2–10% of the optimal scheduling algorithm in these applications, while exhibiting low overhead and little sensitivity to application-dependent parameters.     

Compilers for instruction-level parallelism

Discovering and exploiting instruction level parallelism in code will be key to future increases in microprocessor performance. What technical challenges must compiler writers meet to better use ILP? Instruction level parallelism allows a sequence of instructions derived from a sequential program to be parallelized for execution on multiple pipelined functional units. If industry acceptance is a measure of importance, ILP has blossomed. It now profoundly influences the design of almost all leading edge microprocessors and their compilers. Yet the development of ILP is far from complete, as research continues to find better ways to use more hardware parallelism over a broader class of applications     

Stream parallelism with ordered data constraints on multi-core systems

The Journal of Supercomputing - It is often a challenge to keep input/output tasks/results in order for parallel computations over data streams, particularly when stateless task operators are...     

Exploiting application parallelism in knowledge-based systems: an experimental method

A method is presented which aims to enhance the run-time performance of real-time production systems of utilising natural concurrency in the application knowledge base. This exploiting application parallelism (EAP) method includes an automated analysis of the knowledge base and the use of this analysis information to partition and execute rules on a novel parallel production system (PPS) architecture. Prototype analysis tools and a PPS simulator have been developed for the Inference ART environment in order to apply the method to a naval data-fusion problem. The results of this experimental investigation revealed that an average maximum of 12.06 rule-firings/cycle was possible but, due to serial bottlenecks inherent in the data-fusion problem, up to only 2.14 rule-firings/cycle was achieved overall. Limitations of the EAP method are discussed within the context of the experimental results and an enhanced method is investigated.     

A case study in multi-core parallelism for the reliability evaluation of composite power systems

The probabilistic evaluation of composite power system reliability is an important but computationally intense task that requires the sampling/searching of a large search space. While multiple methods have been used for performing these computations, a remaining area of research is the impact that modern platforms for parallel computation may have on this computation. Studies have been performed in the past, but they have been primarily limited to cluster-based computing. In addition, the most recent works in this area have used outdated technology or been evaluated using smaller test systems. In the modern era, a wide variety of platforms are available for achieving parallelism in computation including options like multi-core processors, clusters, and accelerators. Each of these platforms provides unique opportunities for accelerating computation and exploiting scalability. In order to fill this gap in the research, this study implements and evaluates two methods of parallel computation—batch parallelism and pipeline parallelism—using a multi-core architecture in a cloud computing environment on Amazon Web Services using up to 36 virtual compute cores. Further, the methodologies are contrasted and compared in terms of computation time, speedup, efficiency, and scalability. Results are collected using IEEE reliability test systems, and speedups upwards of 5x are demonstrated across multiple test systems.     

Exploiting thread-level parallelism in the iterative solution of sparse linear systems

We investigate the efficient iterative solution of large-scale sparse linear systems on shared-memory multiprocessors. Our parallel approach is based on a multilevel ILU preconditioner which preserves the mathematical semantics of the sequential method in ILUPACK. We exploit the parallelism exposed by the task tree corresponding to the nested dissection hierarchy (task parallelism), employ dynamic scheduling of tasks to processors to improve load balance, and formulate all stages of the parallel PCG method conformal with the computation of the preconditioner to increase data reuse. Results on a CC-NUMA platform with 16 processors reveal the parallel efficiency of this solution.     

The exception handling effectiveness of POSIX operating systems

Operating systems form a foundation for robust application software, making it important to understand how effective they are at handling exceptional conditions. The Ballista testing system was used to characterize the handling of exceptional input parameter values for up to 233 POSIX functions and system calls on each of 15 widely used operating system (OS) implementations. This identified ways to crash systems with a single call, ways to cause task hangs within OS code, ways to cause abnormal task termination within OS and library code, failures to implement defined POSIX functionality, and failures to report unsuccessful operations. Overall, only 55 percent to 76 percent of the exceptional tests performed generated error codes, depending on the operating system being tested. Approximately 6 percent to 19 percent of tests failed to generate any indication of error despite exceptional inputs. Approximately 1 percent to 3 percent of tests revealed failures to implement defined POSIX functionality for unusual, but specified, situations. Between 18 percent and 33 percent of exceptional tests caused the abnormal termination of an OS system call or library function, and five systems were completely crashed by individual system calls with exceptional parameter values. The most prevalent sources of these robustness failures were illegal pointer values, numeric overflows, and end-of-file overruns     

Evaluating the effectiveness of explanations for recommender systems

When recommender systems present items, these can be accompanied by explanatory information. Such explanations can serve seven aims: effectiveness, satisfaction, transparency, scrutability, trust, persuasiveness, and efficiency. These aims can be incompatible, so any evaluation needs to state which aim is being investigated and use appropriate metrics. This paper focuses particularly on effectiveness (helping users to make good decisions) and its trade-off with satisfaction. It provides an overview of existing work on evaluating effectiveness and the metrics used. It also highlights the limitations of the existing effectiveness metrics, in particular the effects of under- and overestimation and recommendation domain. In addition to this methodological contribution, the paper presents four empirical studies in two domains: movies and cameras. These studies investigate the impact of personalizing simple feature-based explanations on effectiveness and satisfaction. Both approximated and real effectiveness is investigated. Contrary to expectation, personalization was detrimental to effectiveness, though it may improve user satisfaction. The studies also highlighted the importance of considering opt-out rates and the underlying rating distribution when evaluating effectiveness.     

A dynamical systems approach to task-level system integration used to plan and control autonomous vehicle motion

Autonomous systems with multiple senory and effector modules face the problem of coordinating these components while fulfilling tasks such as moving towards a goal and avoiding sensed obstacles. We propose a set of organizational principles for dealing with this problem. The ideas are (a) to plan in terms of task-related variables that abstract from effector degrees of freedom and peripheral sensor coordinates but succinctly capture behavioral constraints; (b) to generate time courses of behavior through a dynamical system of the planning variables. Task constraints, such as targets to be reached, obstables to be avoided, etc. are expressed as parts of the planning dynamics in a principled fashion invoking concepts of the qualitative theory of dynamical systems. System integration is possible in the sense that all information provided by the various sensory modules and all information required by the various effector modules becomes part of the planning dynamics. Compression of such behavioral information is achieved in a second layer in which the relative strengths of different contributions to the planning dynamics are governed by competitive dynamics that separate convergent information, which is integrated by selecting a representative, from non-redundant information, which is kept invariant. The capability of the system to perform stable planning, make planning decisions, and integrate redundant as well as complementary information is demonstrated by software simulations. These include the simulation of control errors on both the effector and the sensor side.     

卫星系统综合效能分析研究

从卫星系统应用角度提出了基于信息支援保障的卫星系统综合效能评估指标体系,并应用层次分析法建立了效能分析的多属性综合评价模型与方法。为量化指标值,提出了基于领域专家知识的定性与定量相结合的量化指标方法。定量分析表明了多属性综合评价方法对复杂系统效能评估是有效的。     

Fusion of loops for parallelism and locality

Loop fusion improves data locality and reduces synchronization in data-parallel applications. However, loop fusion is not always legal. Even when legal, fusion may introduce loop-carried dependences which prevent parallelism. In addition, performance losses result from cache conflicts in fused loops. In this paper, we present new techniques to: (1) allow fusion of loop nests in the presence of fusion-preventing dependences, (2) maintain parallelism and allow the parallel execution of fused loops with minimal synchronization, and (3) eliminate cache conflicts in fused loops. We describe algorithms for implementing these techniques in compilers. The techniques are evaluated on a 56-processor KSR2 multiprocessor and on a 18-processor Convex SPP-1000 multiprocessor. The results demonstrate performance improvements for both kernels and complete applications. The results also indicate that careful evaluation of the profitability of fusion is necessary as more processors are used     

The effectiveness of strategic information systems planning under environmental uncertainty

Researchers have suggested that more extensive strategic information systems planning (SISP) in an uncertain environment produces greater planning success. Managers must decide whether, and if so when, to perform such SISP. Our study tested the effect of SISP phases on planning success in more and less uncertain environments.A questionnaire assessed SISP in terms of strategic awareness, situation analysis, strategy conception, strategy formulation, and strategy implementation planning phases. It inquired about environmental uncertainty as dynamism, heterogeneity, and hostility. Finally, it measured SISP success as a composite of alignment, analysis, cooperation, and capabilities. One hundred and sixty-one IS executives provided data in a postal survey.More extensive strategy formulation uniformly predicted successful planning in more uncertain environments, whereas strategic awareness generally predicted it in less uncertain ones. Strategy conception predicted it in neither more nor less uncertain environments. More extensive planning is thus not uniformly successful in either environment but depends on the nature of the uncertainty.     

Adaptation algorithm for improvement of effectiveness of distributed computer systems

The adaptation of distributed computer systems to changes in their parameters is investigated. The concept of adaptation is based on the correspondence between the control algorithm and the operating system task allocation algorithm on the one hand and the controlled process parameters and those of the distributed computer system hardware and the load on the other. The adaptation to changing parameters and its optimization may be obtained by using the task allocation algorithm. This algorithm, like optimization control programs in multilayer computer control systems, should be activated in discrete moments of time. The problem of trade-off between the cost (overhead) of allocation algorithm computation and the improvement of system effectiveness is discussed. Examples point out the feasibility of this approach.