7466330
Simple Computation-Universal Cellular Spaces
The special izat ion of the theory of cellular spaces (cellular au tomata ) to those spaces which compute par t ia l recursive funct ions is presented. Neighborhood reduct ion and state-set reduct ion are shown to be pa r t i cu la r ly simple in this special theory, and one dimension is proved to be sufficient for computa t ion universa l i ty . Several computa t ion-un iversa l cellular spaces (CUCS's) are exhibi ted which are simple in the sense t h a t each cell has only a small number q of s ta tes and a small number p of neighbors. For example, a 1-dimensional CUCS with pq = 36 is presented. Two quite different proofs of the existence of a I -dimensional CUCS with only two neighbors are given. Final ly , one of the theorems derived is used to settle three open decidabi l i ty questions.
3332151
Blue screen matting
A classical problem of imaging—the matting problem—is separation of a non-rectangular foreground image from a (usually) rectangular background image—for example, in a film frame, extraction of an actor from a background scene to allow substitution of a different background. Of the several attacks on this difficult and persistent problem, we discuss here only the special case of separating a desired foreground image from a background of a constant, or almost constant, backing color. This backing color has often been blue, so the problem, and its solution, have been called blue screen matting. However, other backing colors, such as yellow or (increasingly) green, have also been used, so we often generalize to constant color matting. The mathematics of constant color matting is presented and proven to be unsolvable as generally practiced. This, of course, flies in the face of the fact that the technique is commonly used in film and video, so we demonstrate constraints on the general problem that lead to solutions, or at least significantly prune the search space of solutions. We shall also demonstrate that an algorithmic solution is possible by allowing the foreground object to be shot against two constant backing colors—in fact, against two completely arbitrary backings so long as they differ everywhere.
11923682
PACE: a new approach to dynamic voltage scaling
By dynamically varying CPU speed and voltage, it is possible to save significant amounts of energy while still meeting prespecified soft or hard deadlines for tasks; numerous algorithms have been published with this goal. We show that it is possible to modify any voltage scaling algorithm to minimize energy use without affecting perceived performance and present a formula to do so optimally. Because this formula specifies increased speed as the task progresses, we call this approach PACE (Processor Acceleration to Conserve Energy). This optimal formula depends on the probability distribution of the task's work requirement and requires that the speed be varied continuously. We therefore present methods for estimating the task work distribution and evaluate how effective they are on a variety of real workloads. We also show how to approximate the optimal continuous schedule with one that changes speed a limited number of times. Using these methods, we find we can apply PACE practically and efficiently. Furthermore, PACE is extremely effective. Simulations using real workloads and the standard model for energy consumption as a function of voltage show that PACE can reduce the CPU energy consumption of existing algorithms by up to 49.5 percent, with an average of 20.6 percent, without any effect on perceived performance. The consequent PACE-modified algorithms reduce CPU energy consumption by an average of 65.4 percent relative to no dynamic voltage scaling, as opposed to only 54.3 percent without PACE.
13154758
Design and characterization of the Berkeley multimedia workload
Abstract. The last decade has seen the integration of audio, video, and 3D graphics into existing workloads as well as the emergence of new workloads dominated by the processing of these forms of media. Unfortunately, widely accepted benchmarks which capture these new workloads in a realistic way have not emerged. The goal of this paper is to present the Berkeley multimedia workload, which was developed to facilitate our own studies on architectural support for multimedia. Here we present a survey of existing multimedia benchmarking methods, a description of the Berkeley multimedia workload, as well as a full workload characterization. We also extract a set of computationally important multimedia kernels for future study.
10194960
Secure Remote Authentication Using Biometric Data
Biometric data offer a potential source of high-entropy, secret information that can be used in cryptographic protocols provided two issues are addressed: (1) biometric data are not uniformly distributed; and (2) they are not exactly reproducible. Recent work, most notably that of Dodis, Reyzin, and Smith, has shown how these obstacles may be overcome by allowing some auxiliary public information to be reliably sent from a server to the human user. Subsequent work of Boyen has shown how to extend these techniques, in the random oracle model, to enable unidirectional authentication from the user to the server without the assumption of a reliable communication channel. 
 
We show two efficient techniques enabling the use of biometric data to achieve mutual authentication or authenticated key exchange over a completely insecure (i.e., adversarially controlled) channel. In addition to achieving stronger security guarantees than the work of Boyen, we improve upon his solution in a number of other respects: we tolerate a broader class of errors and, in one case, improve upon the parameters of his solution and give a proof of security in the standard model.
39614676
Branch Target Buffer Design and Optimization
A branch target buffer (BTB) can reduce the performance penalty of branches in pipelined processors by predicting the path of the branch and caching information used by the branch. Two major issues in the design of BTBs that achieves maximum performance with a limited number of bits allocated to the BTB implementation are discussed. The first is BTB management. A method for discarding branches from the BTB is examined. This method discards the branch with the smallest expected value for improving performance; it outperforms the least recently used (LRU) strategy by a small margin, at the cost of additional complexity. The second issue is the question of what information to store in the BTB. A BTB entry can consist of one or more of the following: branch tag, prediction information, the branch target address, and instructions at the branch target. Various BTB designs, with one or more of these fields, are evaluated and compared. >
11584462
The automatic improvement of locality in storage systems
Disk I/O is increasingly the performance bottleneck in computer systems despite rapidly increasing disk data transfer rates. In this article, we propose Automatic Locality-Improving Storage (ALIS), an introspective storage system that automatically reorganizes selected disk blocks based on the dynamic reference stream to increase effective storage performance. ALIS is based on the observations that sequential data fetch is far more efficient than random access, that improving seek distances produces only marginal performance improvements, and that the increasingly powerful processors and large memories in storage systems have ample capacity to reorganize the data layout and redirect the accesses so as to take advantage of rapid sequential data transfer. Using trace-driven simulation with a large set of real workloads, we demonstrate that ALIS considerably outperforms prior techniques, improving the average read performance by up to 50% for server workloads and by about 15% for personal computer workloads. We also show that the performance improvement persists as disk technology evolves. Since disk performance in practice is increasing by only about 8% per year, the benefit of ALIS may correspond to as much as several years of technological progress.