Impact of level-2 cache sharing on the performance and power requirements of homogeneous multicore embedded systems

In order to satisfy the needs for increasing computer processing power, there are significant changes in the design process of modern computing systems. Major chip-vendors are deploying multicore or manycore processors to their product lines. Multicore architectures offer a tremendous amount of processing speed. At the same time, they bring challenges for embedded systems which suffer from limited resources. Various cache memory hierarchies have been proposed to satisfy the requirements for different embedded systems. Normally, a level-1 cache (CL1) memory is dedicated to each core. However, the level-2 cache (CL2) can be shared (like Intel Xeon and IBM Cell) or distributed (like AMD Athlon). In this paper, we investigate the impact of the CL2 organization type (shared Vs distributed) on the performance and power consumption of homogeneous multicore embedded systems. We use VisualSim and Heptane tools to model and simulate the target architectures running FFT, MI, and DFT applications. Experimental results show that by replacing a single-core system with an 8-core system, reductions in mean delay per core of 64% for distributed CL2 and 53% for shared CL2 are possible with little additional power (15% for distributed CL2 and 18% for shared CL2) for FFT. Results also reveal that the distributed CL2 hierarchy outperforms the shared CL2 hierarchy for all three applications considered and for other applications with similar code characteristics.     

Improving the performance of distributed virtual environment systems

The last years have witnessed a dramatic growth in the number as well as in the variety of distributed virtual environment systems. These systems allow multiple users, working on different client computers that are interconnected through different networks, to interact in a shared virtual world. One of the key issues in the design of scalable and cost-effective DVE systems is the partitioning problem. This problem consists of efficiently assigning the existing clients to the servers in the system and some techniques have been already proposed for solving it. This paper experimentally analyzes the correlation of the quality function proposed in the literature for solving the partitioning problem with the performance of DVE systems. Since the results show an absence of correlation, we also propose the experimental characterization of DVE systems. The results show that the reason for that absence of correlation is the nonlinear behavior of DVE systems with regard to the number of clients in the system. DVE systems reach saturation when any of the servers reaches 100 percent of CPU utilization. The system performance greatly decreases if this limit is exceeded in any server. Also, as a direct application of these results, we present a partitioning method that is targeted to keep all the servers in the system below a certain threshold value of CPU utilization, regardless of the amount of network traffic. Evaluation results show that the proposed partitioning method can improve DVE system performance, regardless of both the movement pattern of clients and the initial distribution of clients in the virtual world.     

Study of the performance impact of a cache buffer in solid-state disks

An SSD generally has a small memory, called cache buffer, to increase its performance and the frequently accessed data are maintained in this cache buffer. These cached data must periodically write back to the NAND Flash memory to prevent the data loss due to sudden power-off, and it should immediately flush all dirty data items into a non-volatile storage media (i.e., NAND Flash memory), when receiving a flush command, while the flush command is supported in Serial ATA (SATA) and Serial Attached SCSI (SAS). Thus, a flush command is an important factor to give significant impact on SSD performance.In this paper, we have investigated the impact of a flush command on SSD performance and have conducted in-depth experiments with versatile workloads, using the modified FlashSim simulator. Our performance measurements using PC and server workloads provide several interesting conclusions. First, a cache buffer without a flush command could improve SSD performance as a cache buffer size increases, since more requested data could be handled in the cache buffer. Second, our experiments have revealed that a flush command might give a negative impact on SSD performance. The average response time per request with a flush command is getting worse compared to not supporting the flush command, as cache buffer size increases. Finally, we have proposed the backend flushing scheme to nullify the negative performance impact of the flush command. The backend flushing scheme first writes the requested data into a cache buffer and sends the acknowledgment of the request completion to a host system. Then, it writes back the data in the cache buffer to NAND Flash memory. Thus, the proposed scheme could improve SSD performance since it might reduce the number of the dirty data items in a cache buffer to write back to NAND Flash memory.All these results suggest that a flush command could give a negative impact on SSD performance and our proposed backend flushing scheme could improve the SSD performance while supporting a flush command.     

Improving performance of HMM-based off-line signature verification systems through a multi-hypothesis approach

The neural and statistical classifiers employed in off-line signature verification (SV) systems are often designed from limited and unbalanced training data. In this article, an approach based on the combination of discrete Hidden Markov Models (HMMs) in the ROC space is proposed to improve the performance of these systems. Inspired by the multiple-hypothesis principle, this approach allows the system to select, from a set of different HMMs, the most suitable solution for a given input sample. By training an ensemble of user-specific HMMs with different number of states and different codebook sizes, and then combining these models in the ROC space, it is possible to construct a composite ROC curve that provides a more accurate estimation of system performance. Moreover, in testing mode, the corresponding operating points—which may be selected dynamically according to the risk associated with input samples—can significantly reduce the error rates. Experiments performed by using a real-world off-line SV database, with random, simple and skilled forgeries, indicate that the multi-hypothesis approach can reduce the average error rates by more than 17%, as well as the number of HMM states by 48%.     

Evaluating the performance of FFT library implementations on modern hybrid computing systems

The Journal of Supercomputing - Fast Fourier transform is widely used to solve numerous scientific and engineering problems. In particular, this transform is behind the software dealing with speech...     

Strategic planning of information systems at the corporate level

Strategic issues related to information systems are subject to conflicting trends. One is the more rapid change in environmental factors; the other is the growing complexity of requests that reduce the rate of response. This study examines the basis for concern about current issues. The factors are reviewed in the light of recently published material. Three organizational structures for information system planning are compared in terms of their ability to meet different organizational requirements. Techniques which have been used successfully in the definition of strategic issues and analysis of environmental factors are presented. The object is to aid the integration of information system strategies into the overall strategy of an enterprise.     

Improving the performance of low-gain designs for bounded control of linear systems

Several solutions of the problem of stabilizing linear systems with bounded control rely on a one-parameter family of low-gain linear control laws u=K(ε)x. This paper presents an online scheduling of the parameter ensuring, in addition to closed-loop stability, the fastest possible transient between two extreme values of ε, chosen for stability and performance, respectively.     

Improving the tracking performance of mechanical systems by adaptive extended friction compensation

The paper discusses a tracking control system and shows with simulation and experimental results that extended friction models can be successfully incorporated in a computed-torque-like adaptive control scheme. The friction model used includes Coulomb, viscous, and periodic friction with sense of direction dependent parameters. To get small tracking errors, adaptation of the friction model parameters is necessary. The tracking performance is an order of magnitude better than with PD control. The robustness of the scheme for parameter inaccuracies is sufficient, owing to the adaptation, but the controller gains are limited due to stability problems caused by unmodeled dynamics.     

Adaptive dynamic CMAC neural control of nonlinear chaotic systems with L2 tracking performance

The advantage of using cerebellar model articulation control (CMAC) network has been well documented in many applications. However, the structure of a CMAC network which will influence the learning performance is difficult to select. This paper proposes a dynamic structure CMAC network (DSCN) which the network structure can grow or prune systematically and their parameters can be adjusted automatically. Then, an adaptive dynamic CMAC neural control (ADCNC) system which is composed of a computation controller and a robust compensator is proposed via second-order sliding-mode approach. The computation controller containing a DSCN identifier is the principal controller and the robust compensator is designed to achieve L₂ tracking performance with a desired attenuation level. Moreover, a proportional–integral (PI)-type adaptation learning algorithm is derived to speed up the convergence of the tracking error in the sense of Lyapunov function and Barbalat’s lemma, thus the system stability can be guaranteed. Finally, the proposed ADCNC system is applied to control a chaotic system. The simulation results are demonstrated that the proposed ADCNC scheme can achieve a favorable control performance even under the variations of system parameters and initial point.     

Monitoring the state of the moving train by use of high performance systems and modern computation methods

The objective of this work has been to study the propagation of elastic waves in rails. It presents the comparison of calculations obtained by the grid-characteristic and discontinuous Galerkin methods. The propagation of elastic waves in the presence and absence of the karst inclusion in the ground under the embankment, diagnosed in these cases from the rails, are compared. The wave pictures and diagnosed signals for four types of defects of a fractured character: vertical and horizontal head layering, cross fracture in the head and cracks in the rail web are given. The grid-characteristic method on the curvilinear structural meshes and the discontinuous Galerkin method on the nonstructured triangular meshes make it possible to solve efficiently the tasks on monitoring the state of the moving train and rail, including a great number of integrity violations, dynamic interactions in the train-rail system, and obtain the full wave picture.     

Exploring the speedups of embedded microprocessor systems utilizing a high-performance coprocessor data-path

The speedups achieved in a generic microprocessor system by employing a high-performance data-path are presented. The data-path acts as a coprocessor that accelerates time critical code segments, called kernels, thereby increasing the overall performance. The data-path has been previously introduced by the authors and it is composed by Flexible Computational Components (FCCs) that can realize any two-level template of primitive operations. A design flow, integrating the automated coprocessor synthesis method, for executing applications on the system is presented. For evaluating the effectiveness of our coprocessor approach, analytical exploration in respect to the type of the custom data-path and to the microprocessor architecture is performed. The kernel and the overall application speedups of six real-life applications, relative to the software execution on the microprocessor, are estimated using the design flow. Kernel speedups up to 155 are achieved that result in an average overall improvement of 2.78 with a small overhead in circuit area. The design flow achieved the acceleration of the applications near to theoretical bounds. A comparison with another high-performance data-path showed that the proposed coprocessor achieves better performance while having smaller area-time products for the generated data-paths.

Improving the fingerprint verification performance of set partitioning coders at low bit rates

Multimedia Tools and Applications - Wavelet transform combined with the set partitioning coders (SPC) are the most widely used fingerprint image compression approach. Many different SPC coders have...     

A modelling-based methodology for evaluating the performance of a real-time embedded control system

This paper presents a modelling-based methodology for embedded control system (ECS) design. Here, instead of developing a new methodology for ECS design, we propose to upgrade an existing one by bridging it with a methodology used in other areas of embedded systems design. We created a transformation bridge between the control-scheduling and the hardware/software (HW/SW) co-design tools. By defining this bridge, we allow for an automatic model transformation. As a result, we obtain more accurate timing-behaviour simulations, considering not only the real-time software, but also the hardware architecture’s impact on the control performance. We show an example with different model-evaluation results compared to real implementation measurements, which clearly demonstrates the benefits of our approach.     

Software performance tuning of software product family architectures: Two case studies in the real-time embedded systems domain

Software performance is an important non-functional quality attribute and software performance evaluation is an essential activity in the software development process. Especially in embedded real-time systems, software design and evaluation are driven by the needs to optimize the limited resources, to respect time deadlines and, at the same time, to produce the best experience for end-users. Software product family architectures add additional requirements to the evaluation process. In this case, the evaluation includes the analysis of the optimizations and tradeoffs for the whole products in the family. Performance evaluation of software product family architectures requires knowledge and a clear understanding of different domains: software architecture assessments, software performance and software product family architecture. We have used a scenario-driven approach to evaluate performance and dynamic memory management efficiency in one Nokia software product family architecture. In this paper we present two case studies. Furthermore, we discuss the implications and tradeoffs of software performance against evolvability and maintenability in software product family architectures.     

Measures for evaluating the decision performance of a decision table in rough set theory

As two classical measures, approximation accuracy and consistency degree can be employed to evaluate the decision performance of a decision table. However, these two measures cannot give elaborate depictions of the certainty and consistency of a decision table when their values are equal to zero. To overcome this shortcoming, we first classify decision tables in rough set theory into three types according to their consistency and introduce three new measures for evaluating the decision performance of a decision-rule set extracted from a decision table. We then analyze how each of these three measures depends on the condition granulation and decision granulation of each of the three types of decision tables. Experimental analyses on three practical data sets show that the three new measures appear to be well suited for evaluating the decision performance of a decision-rule set and are much better than the two classical measures.     

Improving the performance of fuzzy rule-based classification systems with interval-valued fuzzy sets and genetic amplitude tuning

Among the computational intelligence techniques employed to solve classification problems, Fuzzy Rule-Based Classification Systems (FRBCSs) are a popular tool because of their interpretable models based on linguistic variables, which are easier to understand for the experts or end-users.The aim of this paper is to enhance the performance of FRBCSs by extending the Knowledge Base with the application of the concept of Interval-Valued Fuzzy Sets (IVFSs). We consider a post-processing genetic tuning step that adjusts the amplitude of the upper bound of the IVFS to contextualize the fuzzy partitions and to obtain a most accurate solution to the problem.We analyze the goodness of this approach using two basic and well-known fuzzy rule learning algorithms, the Chi et al.’s method and the fuzzy hybrid genetics-based machine learning algorithm. We show the improvement achieved by this model through an extensive empirical study with a large collection of data-sets.     

Improving the numerical stability and the performance of a parallel sparse solver

Coarse grain parallel codes for solving sparse systems of linear algebraic equations can be developed in several different ways. The following procedure is suitable for some parallel computers. A preliminary reordering of the matrix is first applied to move as many zero elements as possible to the lower left corner. After that the matrix is partitioned into large blocks and the blocks in the lower left corner contain only zero elements. An attempt to obtain a good load-balance is carried out by allowing the diagonal blocks to be rectangular.

While the algorithm based on the above ideas has good parallel properties, some stability problems may arise during the factorization because the pivotal search is restricted to the diagonal blocks. A simple a priori procedure has been used in a previous version in an attempt to stabilize the algorithm. In this paper it is shown that three enhanced stability devices can successfully be incorporated in the algorithm so that it is further stabilized and, moreover, the parallel properties of the original algorithm are preserved.

The first device is based on a dynamic check of the stability. In the second device a slightly modified reordering is used in an attempt to get more nonzero elements in the diagonal blocks (the number of candidates for pivots tends to increase in this situation and, therefore, there is a better chance to select more stable pivots). The third device applies a P⁵-like ordering as a secondary criterion in the basic reordering procedure. This tends to improve the reordering and the performance of the solver. Moreover, the device is stable, while the original P⁵ ordering is often unstable.

Numerical results obtained by using the three new devices are presented. The well-known sparse matrices from the Harwell-Boeing set are used in the experiments.     

Sounding the warning bells: The need for a systems approach to understanding behaviour at rail level crossings

Collisions at rail level crossings are an international safety concern and have been the subject of considerable research effort. Modern human factors practice advocates a systems approach to investigating safety issues in complex systems. This paper describes the results of a structured review of the level crossing literature to determine the extent to which a systems approach has been applied. The measures used to determine if previous research was underpinned by a systems approach were: the type of analysis method utilised, the number of component relationships considered, the number of user groups considered, the number of system levels considered and the type of model described in the research. None of research reviewed was found to be consistent with a systems approach. It is recommended that further research utilise a systems approach to the study of the level crossing system to enable the identification of effective design improvements.