High Degree Of Concurrency Research Articles

Influence of geography and weather conditions on the navigation and seaborne trade in the Black Sea

The navigation on the Black Sea raises some specific issues that need to be considered, to ensure maximum safety conditions for the ship, crew, and cargo throughout the voyage. Under the current conditions of the global maritime market having a high degree of concurrency, respectively the problem of reducing fuel consumption and reducing the time needed for performing various voyages, especially in crossing the ocean on different routes, is particularly important for ship owners. The economic effect is determined by converting this time into the corresponding cost price, fuel consumption having the main percentage; to these is added the benefits increase by reducing the period of undertaking the transport contract.

An Open-Source Platform for High-Performance Non-Coherent On-Chip Communication

On-chip communication infrastructure is a central component of modern systems-on-chip (SoCs), and it continues to gain importance as the number of cores, the heterogeneity of components, and the on-chip and off-chip bandwidth continue to grow. Decades of research on on-chip networks enabled cache-coherent shared-memory multiprocessors. However, communication fabrics that meet the needs of heterogeneous many-cores and accelerator-rich SoCs, which are not, or only partially, coherent, are a much less mature research area. In this work, we present a modular, topology-agnostic, high-performance on-chip communication platform. The platform includes components to build and link subnetworks with customizable bandwidth and concurrency properties and adheres to a state-of-the-art, industry-standard protocol. We discuss microarchitectural trade-offs and timing/area characteristics of our modules and show that they can be composed to build high-bandwidth (e.g., 2.5 GHz and 1024 bit data width) end-to-end on-chip communication fabrics (not only network switches but also DMA engines and memory controllers) with high degrees of concurrency. We design and implement a state-of-the-art ML training accelerator, where our communication fabric scales to 1024 cores on a die, providing 32 TB/s cross-sectional bandwidth at only 24 ns round-trip latency between any two cores.

Ensuring Appropriateness of Pediatric Second Opinion Consultations

PurposeWe sought to evaluate discrepancy rates between outside interpretations, radiology trainee preliminary reports, and subspecialist attending final interpretations for pediatric second opinion consultations on plain film and computed tomography imaging and to evaluate the impact of a process improvement for second opinion consultations. MethodsOf a total of 572 requests for second opinion consultations during 1-year preintervention period, we utilized RADPEER to score concurrence of 158 requests which occurred overnight and included outside radiologist interpretations and resident preliminary reports. In consultation with clinician committees, we developed new guidelines for requesting second opinion consultations. We evaluated the impact on the number of consultations for the 1-year period following implementation of this process improvement. ResultsThere was concurrence between the outside interpretation and pediatric subspecialist second opinion in 146 of 158 cases (92%). There was concurrence between the radiology resident and pediatric subspecialist second opinion in 145 of 158 cases (92%). During the 1-year period following our process improvement implementation, the total number of second opinion consultations decreased to 185 (from 572, a decrease of 68%) and the number of overnight requests for resident preliminary reports decreased to 11 (from 158, a decrease of 93%). ConclusionsThere was a high degree of concurrence between interpretations provided by outside radiologists, overnight radiology residents, and attending pediatric radiologists at our institution. Analyzing institutional-specific discrepancy rates is a valuable first step in partnering with clinicians to develop appropriate guidelines for second opinion consultations.

An intelligent household greenhouse system design based on Internet of Things

In order to combine indoor greenery conservation with Internet of Things Technologies, this paper designs an intelligent household greenhouse project with the features of comprehensive sensing, reliable transmission and intelligent processing. Through the analysis of functional requirements of the intelligent household greenhouse system, an intelligent household greenhouse system is designed with the functions of greenhouse environmental data detection, greenhouse environmental control regulation, data remote transmission and human-computer interaction. Its sensor layer collects environmental data in real time based onthe ZigBee wireless sensor network. The network layer STM32 intelligent gateway coordinates with network server, so as to exchange data from sensor layer to application layer, and solve the problems of non-blocking of data sending and receiving as well as concurrent requests of multiple mobile terminals. The application layer is designed into two types. One is a desktop management system as a data storage and analysis center, and the other is a mobile terminal APP. At the same time, we design a communication protocol that is applicable to the interaction of the three-layer structure of the Internet of Things, with the characteristics of simplicity, stability, readability, and scalability. It can avoid the mutual influence of multi-level data exchange and ensure the correctness of data circulation. In the design, the system sensor layer ensures stable transmission of various data and instructions, and the network layer has a high degree of concurrency and real time. And various measurement and control data of the sensor layer can interact with the data of mobile-terminal equipment of the application layer. What’s more, the desktop management system and mobile terminal APP can monitor greenhouse data in real time and control various actuators in the greenhouse.

A Method for Prediction of Femoral Component of Hip Prosthesis Durability due to Aseptic Loosening by Using Coffin/Manson Fatigue Model.

The purpose of this work is to develop a new model estimate of the fatigue life of a hip prosthesis due to aseptic loosening as a multifactorial phenomenon. The formula developed here is a three-parameter model based on Basquin's law for fatigue, eccentric compression formula for the compressive stress and torsion in the prosthesis due to the horizontal components of the contact force. With our model, we can accurately predict the durability of a hip prosthesis due to the following four parameters: body weight, femoral offset, duration, and intensity of daily physical activities of a patient. The agreement of the prediction with the real life of the prosthesis, observed on 15 patients, is found to be adequate. Based on the formula derived for a particular implant, there was a high degree of concurrence between the model-predicted and actual values of aseptic loosening (durability) proved by the Mann–Whitney U test. By virtue of the validated model, it is possible to predict, quantitatively, the influence of various factors on the hip life. For example, we can conclude that a 10% decrease of a patient's body mass, with all other conditions being the same, causes 5% increase of the hip fatigue life.

Persistent hybrid transactional memory for databases

Processors with hardware support for transactional memory (HTM) are rapidly becoming commonplace, and processor manufacturers are currently working on implementing support for upcoming non-volatile memory (NVM) technologies. The combination of HTM and NVM promises to be a natural choice for in-memory database synchronization. However, limitations on the size of hardware transactions and the lack of progress guarantees by modern HTM implementations prevent some applications from obtaining the full benefit of hardware transactional memory. In this paper, we propose a persistent hybrid TM algorithm called PHyTM for systems that support NVM and HTM. PHyTM allows hardware assisted ACID transactions to execute concurrently with pure software transactions, which allows applications to gain the benefit of persistent HTM while simultaneously accommodating unbounded transactions (with a high degree of concurrency). Experimental simulations demonstrate that PHyTM is fast and scalable for realistic workloads.

Efficient Approximation Algorithms for Weighted $b$-Matching

We describe a half-approximation algorithm, $b$-Suitor, for computing a $b$-Matching of maximum weight in a graph with weights on the edges. $b$-Matching is a generalization of the well-known Matching problem in graphs, where the objective is to choose a subset of $M$ edges in the graph such that at most a specified number $b(v)$ of edges in $M$ are incident on each vertex $v$. Subject to this restriction we maximize the sum of the weights of the edges in $M$. We prove that the $b$-Suitor algorithm computes the same $b$-Matching as the one obtained by the Greedy algorithm for the problem. We implement the algorithm on serial and shared-memory parallel processors and compare its performance against a collection of approximation algorithms that have been proposed earlier. Our results show that the $b$-Suitor algorithm outperforms the Greedy and locally dominant edge algorithms by one to two orders of magnitude on a serial processor. The $b$-Suitor algorithm has a high degree of concurrency, and it scales we...

Semantics, distributed implementation, and formal analysis of KLAIM models in Maude

Emerging distributed systems such as cloud-based services are characterized by computations over different explicit localities, moving code and data, and a high degree of concurrency. KLAIM is a well-established language that can naturally describe such systems. The KLAIM language is process algebra flavored, allows Linda-based asynchronous communication through distributed tuple spaces, and supports explicit localities as well as code and data mobility. In this work we take some first steps in the quest for a correct-by-construction design process for secure and reliable distributed systems. Such a design process is necessary as more and more safety- and security-critical tasks that need to satisfy mission-critical formal requirements are executed in a distributed setting. We use a rewriting-based approach to formally specify and analyze KLAIM specifications of distributed systems. In particular we: (i) specify the reduction semantics of KLAIM in Maude, (ii) extend the Maude-based specification by making messages first-class citizens, and (iii) describe a second extension that allows true distributed execution of Maude-based KLAIM specifications. We prove that under appropriate weak fairness assumptions all these specifications are stuttering bisimilar and that large classes of logic temporal formulas, namely all CTL⁎∖X formulas, are preserved. By means of an example we show that our approach allows specifying aspects of a distributed system in a Maude-based KLAIM dialect, verifying these specifications using Maude's LTL model checking capabilities, and then executing the verified specifications in a distributed environment. This marks a first step in the quest for a correct-by-construction design process for secure and reliable distributed systems.

Reducing database locking contention through multi-version concurrency

In multi-version databases, updates and deletions of records by transactions require appending a new record to tables rather than performing in-place updates. This mechanism incurs non-negligible performance overhead in the presence of multiple indexes on a table, where changes need to be propagated to all indexes. Additionally, an uncommitted record update will block other active transactions from using the index to fetch the most recently committed values for the updated record. In general, in order to support snapshot isolation and/or multi-version concurrency, either each active transaction is forced to search a database temporary area (e.g., roll-back segments) to fetch old values of desired records, or each transaction is forced to scan the entire table to find the older versions of the record in a multi-version database (in the absence of specialized temporal indexes). In this work, we describe a novel kV-Indirection structure to enable efficient (parallelizable) optimistic and pessimistic multi-version concurrency control by utilizing the old versions of records (at most two versions of each record) to provide direct access to the recent changes of records without the need of temporal indexes. As a result, our technique results in higher degree of concurrency by reducing the clashes between readers and writers of data and avoiding extended lock delays. We have a working prototype of our concurrency model and kV-Indirection structure in a commercial database and conducted an extensive evaluation to demonstrate the benefits of our multi-version concurrency control, and we obtained orders of magnitude speed up over the single-version concurrency control.

Maximizing Active Storage Resources with Deadlock Avoidance in Workflow-Based Computations

Workflow-based workloads usually consist of multiple instances of the same workflow, which are jobs with control or data dependencies to carry out a well-defined scientific computation task, with each instance acting on its own input data. To maximize the performance, a high degree of concurrency is always achieved by running multiple instances simultaneously. However, since the amount of storage is limited on most systems, deadlock due to oversubscribed storage requests is a potential problem. To address this problem, we integrate two novel concepts with the traditional problem of deadlock avoidance by proposing two algorithms that can maximize active (not just allocated) resource utilization and minimize makespan. Our approach is based on the well-known banker's algorithm, but our algorithms make the important distinction between active and inactive resources, which is not a part of previous approaches. The central idea is to leverage the data-flow information to dynamically approximate localized maximum claim (i.e., the resource requirements of the remaining jobs of the instance) to improve either interinstance or intrainstance concurrency and still avoid deadlock. Through simulation-based studies, we show how our proposed algorithms are better than the classic banker's algorithm and the more recent Lang's algorithm in terms of makespan and active storage resource utilization.

Performance of program modification techniques that ensure serializable executions with snapshot isolation DBMS

Snapshot Isolation (SI) is a multiversion concurrency control that has been implemented by several open source and commercial database systems (Oracle, Microsoft SQL Server, and previous releases of PostgreSQL). The main feature of SI is that a read operation does not block a write operation and vice versa, which allows higher degree of concurrency than traditional two-phase locking. SI prevents many anomalies that appear in other isolation levels, but it still can result in non-serializable executions, in which database integrity constraints can be violated. Several techniques are known to modify the application code based on preanalysis, in order to ensure that every execution is serializable on engines running SI. We introduce a new technique called External Lock Manager (ELM). In using a technique, there is a choice to make, of which pairs of transactions need to have conflicts introduced. We measure the performance impact of the choices available, among techniques and conflicts.

DDS: A deadlock detection-based scheduling algorithm for workflow computations in HPC systems with storage constraints

Workflow-based workloads usually consist of multiple instances of the same workflow, which are jobs with control or data dependencies, to carry out a well-defined scientific computation task, with each instance acting on its own input data. To maximize throughput performance, a high degree of concurrency is achievable by running multiple instances simultaneously. However, deadlock is a potential problem when storage is constrained. To address this problem, we design and evaluate a deadlock detection-based scheduling (DDS) algorithm that can achieve high performance by making the best use of the available storage resources. Our algorithm takes advantages of the dataflow information of the workflow to speculatively schedule each instance if the instant storage is sufficient for some constituent jobs, but not necessarily for the whole workflow instance. Whenever deadlock or a performance anomaly is detected, some selected in-progress workflow instances are required to be rollbacked to release storage for other blocked jobs. We develop a suite of strategies to select the victims and beneficiaries (instances or jobs) and evaluate their performance via a simulation-based study. Our results show that the DDS algorithm can adapt the job concurrency to the available storage resources and achieve higher performance than some deadlock avoidance methods in our synthetic and real workflow computations.

Increasing data locality and introducing Level-3 BLAS in the Neville elimination

In this paper we present two new algorithmic variants to compute the Neville elimination, with and without pivoting, which improve data locality and cast most of the computations in terms of high-performance Level 3 BLAS. The experimental evaluation on a state-of-the-art multi-core processor demonstrates that the new blocked algorithms exhibit a much higher degree of concurrency and better cache usage, yielding higher performance while offering numerical accuracy akin to that of the traditional columnwise variant in most cases.

Edge Partitioning in Parallel Structured Duplicate Detection

We show how edge partitioning, a technique originally developed for external-memory search, can be used to reduce the number of slow synchronization operations needed in parallel graph search. We show that edge partitioning improves on a previous technique called parallel structured duplicate detection by allowing a higher degree of concurrency, even for search problems with little or no inherent locality. For domain-independent graph search, we also show that edge partitioning significantly improves search speed by improving the efficiency of precondition checking. We demonstrate the effectiveness of this approach to parallel graph search for domain-independent STRIPS planning.

A uniform process alternator for arbitrary topologies

We introduce an alternator with uniform processes that executes in a process graph of arbitrary topology. In general, alternators are free from deadlock, protect against simultaneous execution of the critical sections of dependent processes, and after a finite number of executions provide a high degree of concurrency and some degree of fairness (deterministically or stochastically). Because this alternator has uniform processes, strong fairness and concurrency are properties obtained after a finite number of steps with an arbitrary probability, due to the possibility of symmetry in states. The size of the state space and the periodicity of critical section execution are dependent upon the initial state. The worst case size of the state space utilized and period between critical sections executions depend upon the diameter of the graph of processes. An important value of alternators is their capacity for transforming systems correct under serial (interleaving) semantics to systems correct under concurrent or maximal (power set) semantics. This property is based upon a graph of processes representing the alternator in which the vertices are processes and the edges are dependencies between processes.

Fast and Accurate Generalized Harmonic Analysis and Its Parallel Computation by GPU

A fast and accurate method for Generalized Harmonic Analysis is proposed. The proposed method estimates the parameters of a sinusoid and subtracts it from a target signal one by one. The frequency of the sinusoid is estimated around a peak of Fourier spectrum using binary search. The binary search can control the trade-off between the frequency accuracy and the computation time. The amplitude and the phase are estimated to minimize the squared sum of the residue after extraction of estimated sinusoids from the target signal. Sinusoid parameters are recalculated to reduce errors introduced by the peak detection using windowed Discrete-Time Fourier Transform. Audio signals are analyzed by the proposed method, which confirms the accuracy compared to existing methods. The proposed algorithm has high degree of concurrency and is suitable to be implemented on Graphical Processing Unit (GPU). The computational throughput can be made higher than the input audio signal rate.

Tolerating byzantine faults in transaction processing systems using commit barrier scheduling

This paper describes the design, implementation, and evaluation of areplication scheme to handle Byzantine faults in transaction processing database systems. The scheme compares answers from queries and updates on multiple replicas which are unmodified, off-the-shelf systems, to provide a single database that is Byzantine fault tolerant. The scheme works when the replicas are homogeneous, but it also allows heterogeneous replication in which replicas come from different vendors. Heterogeneous replicas reduce the impact of bugs and security compromises because they are implemented independently and are thus less likely to suffer correlated failures. The main challenge in designing a replication scheme for transactionprocessing systems is ensuring that the different replicas execute transactions in equivalent serial orders while allowing a high degreeof concurrency. Our scheme meets this goal using a novel concurrency control protocol, commit barrier scheduling (CBS). We have implemented CBS in the context of a replicated SQL database, HRDB(Heterogeneous Replicated DB), which has been tested with unmodified production versions of several commercial and open source databases as replicas. Our experiments show an HRDB configuration that can tolerate one faulty replica has only a modest performance overhead(about 17% for the TPC-C benchmark). HRDB successfully masks several Byzantine faults observed in practice and we have used it to find a new bug in MySQL.

Performance of particle in cell methods on highly concurrent computational architectures

Particle in cell (PIC) methods are effective in computing Vlasov-Poisson system of equations used in simulations of magnetic fusion plasmas. PIC methods use grid based computations, for solving Poisson's equation or more generally Maxwell's equations, as well as Monte-Carlo type methods to sample the Vlasov equation. The presence of two types of discretizations, deterministic field solves and Monte-Carlo methods for the Vlasov equation, pose challenges in understanding and optimizing performance on today large scale computers which require high levels of concurrency. These challenges arises from the need to optimize two very different types of processes and the interactions between them. Modern cache based high-end computers have very deep memory hierarchies and high degrees of concurrency which must be utilized effectively to achieve good performance. The effective use of these machines requires maximizing concurrency by eliminating serial or redundant work and minimizing global communication. A related issue is minimizing the memory traffic between levels of the memory hierarchy because performance is often limited by the bandwidths and latencies of the memory system. This paper discusses some of the performance issues, particularly in regard to parallelism, of PIC methods. The gyrokinetic toroidal code (GTC) is used for these studies and a new radial grid decomposition is presented and evaluated. Scaling of the code is demonstrated on ITER sized plasmas with up to 16K Cray XT3/4 cores.

Multiprogrammed non-blocking checkpoints in support of optimistic simulation on myrinet clusters

CCL (checkpointing and communication library) is a software layer in support of optimistic parallel discrete event simulation (PDES) on myrinet-based COTS clusters. Beyond classical low latency message delivery functionalities, this library implements CPU offloaded, non-blocking (asynchronous) checkpointing functionalities based on data transfer capabilities provided by a programmable DMA engine on board of myrinet network cards. These functionalities are unique since optimistic simulation systems conventionally rely on checkpointing implemented as a synchronous, CPU-based data copy. Releases of CCL up to v2.4 only support monoprogrammed non-blocking checkpoints. This forces re-synchronization between CPU and DMA activities, which is a potential source of overhead, each time a new checkpoint request must be issued at the simulation application level while the last issued one is still being carried out by the DMA engine. In this paper we present a redesigned release of CCL (v3.0) that, exploiting hardware capabilities of more advanced myrinet clusters, supports multiprogrammed non-blocking checkpoints. The multiprogrammed approach allows higher degree of concurrency between checkpointing and other simulation specific operations carried out by the CPU, with benefits on performance. We also report the results of the experimental evaluation of those benefits for the case of a Personal Communication System (PCS) simulation application, selected as a real world test-bed.

Route planning for automated guided vehicles in a manufacturing facility

Automated guided vehicles (AGVs) are widely used in manufacturing and transporting facilities for the movement of material from one location to another. Research in this area is directed toward the development of a path layout design and routing algorithms for movements of materials. The problem is to design a path layout and a routing algorithm that will route the AGVs along the bi-directional path so that the distance travelled will be minimized. This paper presents a bi-directional path flow layout and a routing algorithm that guarantee conflict-free, shortest-time routes for AGVs. Based on the path layout, a routing algorithm and sufficient, but necessary, conditions, mathematical relationships are developed among certain key parameters of vehicle and path. A high degree of concurrency is achieved in vehicle movement. Routing efficiency is analysed in terms of the distance travelled and the time required for AGVs to complete all pickup and drop-off jobs. Numerical results are presented to compare the performance of the proposed model. The research provides the foundation for a bi-directional path layout design and routing algorithms that will aid the designer to develop complicated path layouts.