An empirical evaluation of performance-memory trade-offs in timewarp

The performance of the Time Warp mechanism is experimentally evaluated when only a limited amount of memory is available to the parallel computation. An implementation of the cancelback protocol is used for memory management on a shared memory architecture, viz., KSR to evaluate the performance vs. memory tradeoff. The implementation of the cancelback protocol supports canceling back more than one memory object when memory has been exhausted (the precise number is referred to as the salvage parameter) and incorporates a non-work-conserving processor scheduling technique to prevent starvation. Several synthetic and benchmark programs are used that provide interesting stress cases for evaluating the limited memory behavior. The experiments are extensively monitored to determine the extent to which various factors may affect performance. Several observations are made by analyzing the behavior of Time Warp under limited memory: (1) Depending on the available memory and asymmetry in the workload, canceling back several memory objects at one time (i.e. a salvage parameter value of more than one) improves performance significantly, by reducing certain overheads. However, performance is relatively insensitive to the salvage parameter except at extreme values. (2) The speedup vs. memory curve for Time Warp programs has a well-defined knee before which speedup increases very rapidly with memory and beyond which there is little performance gain with increased memory. (3) A performance nearly equivalent to that with large amounts of memory can be achieved with only a modest amount of additional memory beyond that required for sequential execution, if memory management overheads are small compared to the event granularity. These results indicate that contrary to the common belief, memory usage by Time Warp can be controlled within reasonable limits without any significant loss of performance     

An evaluation of design trade-offs in a high-performance, media-on-demand server

We present a high-performance solution to the I/O retrieval problem in a distributed multimedia system. Parallelism of data retrieval is achieved by striping the data across multiple disks. We identify the components that contribute to media data-retrieval delay. The variable delays among these have a great bearing on the server throughput under varying load conditions. We present a buffering scheme to minimize these variations. We have implemented our model on the Intel Paragon parallel computer. The results of component-wise instrumentation of the server operation are presented and analyzed. Experimental results that demonstrate the efficacy of the buffering scheme are presented. Based on our experiments, a dynamic admission-control policy that takes server workloads into account is proposed.     

A parametric-based performance evaluation and design trade-offs for interconnect architectures using FPGAs for networks-on-chip

Network-on-Chip (NoC) interconnect fabrics are categorized according to trade-offs among latency, throughput, speed, and silicon area, and the correctness and performance of these fabrics in Field-Programmable Gate Array (FPGA) applications are assessed through experimentation and simulation. In this paper, we propose a consistent parametric method for evaluating the FPGA performance of three common on-chip interconnect architectures namely, the Mesh, Torus and Fat-tree architectures. We also investigate how NoC architectures are affected by interconnect and routing parameters, and demonstrate their flexibility and performance through FPGA synthesis and testing of 392 different NoC configurations. In this process, we found that the Flit Data Width (FDW) and Flit Buffer Depth (FBD) parameters have the heaviest impact on FPGA resources, and that these parameters, along with the number of Virtual Channels (VCs), significantly affect reassembly buffering and routing and logic requirements at NoC endpoints. Applying our evaluation technique to a detailed and flexible cycle accurate simulation, we drive the three NoC architectures using benign (Nearest Neighbor and Uniform) and adversarial (Tornado and Random Permutation) traffic patterns with different numbers of VCs, producing a set of load–delay curves. The results show that by strategically tuning the router and interconnect parameters, the Fat-tree network produces the best utilization of FPGA resources in terms of silicon area, clock frequency, critical path delays, network cost, saturation throughput, and latency, whereas the Mesh and Torus networks showed comparatively high resource costs and poor performance under adversarial traffic patterns. From our findings it is clear that the Fat-tree network proved to be more efficient in terms of FPGA resource utilization and is compliant with the current Xilinx FPGA devices. This approach will assist engineers and architects in establishing an early decision in the choice of right interconnects and router parameters for large and complex NoCs. We demonstrate that our approach substantially improves performance under a large variety of experimentation and simulation which confirm its suitability for real systems.     

Customizing floating-point units for FPGAs: Area-performance-standard trade-offs

The high integration density of current nanometer technologies allows the implementation of complex floating-point applications in a single FPGA. In this work the intrinsic complexity of floating-point operators is addressed targeting configurable devices and making design decisions providing the most suitable performance-standard compliance trade-offs. A set of floating-point libraries composed of adder/subtracter, multiplier, divisor, square root, exponential, logarithm and power function are presented. Each library has been designed taking into account special characteristics of current FPGAs, and with this purpose we have adapted the IEEE floating-point standard (software-oriented) to a custom FPGA-oriented format. Extended experimental results validate the design decisions made and prove the usefulness of reducing the format complexity.     

Robust high-order repetitive control: Optimal performance trade-offs

High-order repetitive control has previously been introduced to either improve the robustness for period-time uncertainty or reduce the sensitivity for non-periodic inputs of standard repetitive control schemes. This paper presents a systematic, semidefinite programming based approach to compute high-order repetitive controllers that yield an optimal trade-off between these two performance criteria. The methodology is numerically illustrated through trade-off curves for various controller orders and levels of period-time uncertainty. Moreover, existing high-order repetitive control approaches are shown to correspond to specific points on these curves.     

Design trade-offs in self-management technology: the HeartMan case

ABSTRACT

Health self-management technology has the potential to significantly improve the Quality of Life of patients suffering from chronic diseases. However, designing the technology involves numerous highly context-dependent design decisions. In this paper, we analyse a case study of self-monitoring technology in the field of congestive heart failure. We analyse the design process of the technology from the perspective of design trade-offs. Three important trade-offs related to health self-monitoring technology are described in detail, related to patient autonomy, technology appropriation, and patient well-being. For each of the trade-offs, various mediating factors that influence design decisions are described in detail. On a practical level, this analysis can inform future developments in self-management technology. In addition, this design trade-off analysis provides intermediary knowledge that can contribute to a better theoretical understanding of health self-management technology.     

Computing trade-offs in robust design: Perspectives of the mean squared error

Researchers often identify robust design as one of the most effective engineering design methods for continuous quality improvement. When more than one quality characteristic is considered, an important question is how to trade off robust design solutions. In this paper, we consider a bi-objective robust design problem for which Pareto solutions of two quality characteristics need to be obtained. In practical robust design applications, a second-order polynomial model is adequate to accommodate the curvature of process mean and variance functions, thus mean-squared robust design models, frequently used by many researchers, would contain fourth-order terms. Consequently, the associated Pareto frontier might be non-convex and supported and non-supported efficient solutions needs to be generated. So, the objective of this paper is to develop a lexicographic weighted-Tchebycheff based bi-objective robust design model to generate the associated Pareto frontier. Our numerical example clearly shows the advantages of this model over frequently used weighted-sums model.     

Time-space trade-offs for compressed suffix arrays

Given a binary string of length n, we give a representation of its suffix array that takes O(nt(lgn)^1/t) bits of space such that given i,1?i?n, the ith entry in the suffix array of the string can be retrieved in O(t) time, for any parameter 1?t?lglgn. For t=lglgn, this gives a compressed suffix array representation of Grossi and Vitter [Proc. Symp. on Theory Comput., 2000, pp. 397-406]. For t=O(1/ε), this gives the best known (in terms of space) compressed suffix array representation with constant query time. From this representation one can construct a suffix tree structure for a text of length n, that uses o(nlgn) bits of space which can be used to find all the k occurrences of a given pattern of length m in O(m/lgn+k) time. No such structure was known earlier.     

Analyzing packaging trade-offs during system design

Integrating packaging trade-off analysis with functional verification and architectural design results in a complete virtual prototyping solution far optimizing complex electronic systems. The authors discuss the role of packaging costs in system design and present examples highlighting packaging design trade-offs     

Performance trade-offs for microprocessor cache memories

Design trade-offs for integrated microprocessors caches are examined. A model of cache utilization is introduced to evaluate the effects on cache performance of varying the block size. By considering the overhead cost of sorting address tags and replacement information along with data, it is found that large block sizes lead to more cost-effective cache designs than predicted by previous studies. When the overhead cost is high, caches that fetch only partial blocks on a miss perform better than similar caches that fetch entire blocks. This study indicates that lessons from mainframe and minicomputer design practice should be critically examined to benefit the design of microprocessors     

Fundamental trade-offs in aggregate packet scheduling

In this paper, we investigate the fundamental trade-offs in aggregate packet scheduling for support of guaranteed delay service. In our study, we consider two classes of aggregate packet scheduling algorithms: the static earliest time first (SETF) and dynamic earliest time first (DETF). Through these two classes of aggregate packet scheduling (and together with the simple FIFO packet scheduling algorithm), we show that, with additional timestamp information encoded in the packet header for scheduling purposes, we can significantly increase the maximum allowable network utilization level, while, at the same time, reducing the worst-case edge-to-edge delay bound. Furthermore, we demonstrate how the number of the bits used to encode the timestamp information affects the trade-off between the maximum allowable network utilization level and the worst-case edge-to-edge delay bound. In addition, the more complex DETF algorithms have far superior performance than the simpler SETF algorithms. These results illustrate the fundamental trade-offs in aggregate packet scheduling algorithms and shed light on their provisioning power in support of guaranteed delay service.     

Evaluating early prototypes in context: trade-offs, challenges, and successes

We would like to say that experience prototyping and Wizard of Oz prototyping, taken together, constitute a suitable alternative to true contextual evaluation for early prototypes, one gaining realism at the expense of impartiality, the other impartiality at the expense of realism. As our experiences show, however, each pervasive application design poses unique challenges that you must consider when applying these approaches. Regardless, it's often a good trade-off to sacrifice some measure of realism to evaluate early prototypes. Evaluation of early pervasive computing prototypes in context is a pragmatic exercise, but one that is nonetheless informed by general approaches that reflect and adapt to the challenges of pervasive application development.     

Bounds and trade-offs for Double-Base Number Systems

During the past twenty years, elliptic curves have attracted more and more attention from the cryptography community. One of the core operations of elliptic curve cryptography protocols is the scalar multiplication. Any algorithm reducing the complexity of such multiplications will speed up cryptographic primitives based on these algebraic structures. In this paper, we study two recently introduced techniques for scalar multiplication: Double-Base Number System (DBNS) and Double-Base Chain (DBC). Our results are twofold. First, we demonstrate a theoretical bound on the length of any DBC used to decompose some -bit integers. Second, we present a new algorithm to obtain a {2,3}-integer expansion of n. The bound previously computed will imply the optimality of this algorithm. Our scheme represents a trade-off method between the DBNS approach and the DBC technique. Experimentally, our algorithm constructs shorter chains on average than both the binary/ternary method and the greedy algorithm approach.     

Enhanced qualitative probabilistic networks for resolving trade-offs

Qualitative probabilistic networks were designed to overcome, to at least some extent, the quantification problem known to probabilistic networks. Qualitative networks abstract from the numerical probabilities of their quantitative counterparts by using signs to summarise the probabilistic influences between their variables. One of the major drawbacks of these qualitative abstractions, however, is the coarse level of representation detail that does not provide for indicating strengths of influences. As a result, the trade-offs modelled in a network remain unresolved upon inference. We present an enhanced formalism of qualitative probabilistic networks to provide for a finer level of representation detail. An enhanced qualitative probabilistic network differs from a basic qualitative network in that it distinguishes between strong and weak influences. Now, if a strong influence is combined, upon inference, with a conflicting weak influence, the sign of the net influence may be readily determined. Enhanced qualitative networks are purely qualitative in nature, as basic qualitative networks are, yet allow for resolving some trade-offs upon inference.     

Strategic reasoning under trade-offs between action costs andadvantages

The paper proposes a model for making the most opportune choice among a number of alternatives in situations involving trade-offs and uncertainty. Alternative actions are evaluated on the basis of strategic attributes, such as cost and effectiveness, and the choice is dynamically determined. The issue is addressed by proposing a set of rules (trade-off rules) representing strategic knowledge specifically oriented to solve trade-off problems. Trade-off rules are encoded in conditional sentences such as: “if P then Ci is preferred to Cj”, where P specifies a condition that must be satisfied by the strategic attributes associated with two candidate alternatives, and Ci and Cj are general selection criteria such as “select alternative with the minimum (or maximum) value of a specific attribute ATTR”. In the first part of the paper, a deep analysis of various trade-off problems and various interdependencies among choices is presented. The second part proposes a general paradigm for strategic reasoning under trade-offs. The paradigm is evaluated using a diagnostic application in the medical domain. Finally, the proposal is discussed in the context of related work     

Thematic labelling from hyperspectral remotely sensed imagery: trade-offs in image properties

The effect of spatial, spectral and noise degradations on the accuracy of two highly contrasting thematic labelling scenarios was investigated. The study used hyperspectral imagery of a site near Falmouth, UK, to assess the effect of the data degradations on the accuracy of supervised classification when the H-resolution scene model was applicable and on labelling when an L-resolution scene model was applicable and no ground data were available. In both scenarios, the spatial, spectral and noise degradations affected the accuracy of labelling. However, over the range of degradations investigated, the noise content of the data was consistently noted to be a major variable affecting the accuracy of labelling.     

Understanding value co-creation in virtual communities: The key role of complementarities and trade-offs

Virtual communities form the principal environment favoring provider-client interaction. However, questions regarding the way to manage these communities so that they might generate value have yet to be resolved. Following an inductive approach, seven Lego virtual communities, classified following their governance form and objectives, were analyzed. It is found that different kinds of virtual communities appear as complementary tools to favor value co-creation and enhance members’ performance by constituting a system of value co-creation. Moreover, these community features can help firms achieve a better adjustment between their strategies and their decision-making process relative to the use of social networks.