14886642
Managing multiple disjoint priority orders in priority queues
In communication and computer systems, autonomous sources may assign priorities to their messages or jobs locally and independently. When a remote service (e.g., message transmission or RPC) is requested at a shared server, the server cannot use priority scheduling schemes effectively unless it can make a comparison between priorities defined by individual sources. The authors investigate the strategies under which the service received by requests of one source is not affected by the priority assignments at other sources. The first approach is a combination of processor-sharing and priority queue strategies. The second approach is to map locally defined priorities onto a global priority system. The performance of these approaches is examined in terms of the average response time of all requests, the average response time of the highest priority requests and a fairness measure.<<ETX>>
10753893
Evaluation of Error Recovery Blocks Used for Cooperating Processes
Three alternatives for implementing recovery blocks (RB's) are conceivable for backward error recovery in concurrent processing. These are the asynchronous, synchronous, and the pseudorecovery point implementations. Asynchronous RB's are based on the concept of maximum autonomy in each of concurrent processes. Consequently, establishment of RB's in a process is made independently of others and unbounded rollback propagations become a serious problem. In order to completely avoid unbounded rollback propagations, it is necessary to synchronize the establishment of recovery blocks in all cooperating processes. Process autonomy is sacrificed and processes are forced to wait for commitments from others to establish a recovery line, leading to inefficiency in time utilization. As a compromise between asynchronous and synchronous RB's we propose to insert pseudorecovery points (PRP's) so that unbounded rollback propagations may be avoided while maintaining process autonomy. We developed probabilistic models for analyzing these three methods under standard assumptions in computer performance analysis, i.e., exponential distributions for related random variables. With these models we have estimated 1) the interval between two successive recovery lines for asynchronous RB's, 2) mean loss in computation power for the synchronized method, and 3) additional overhead and rollback distance in case PRP's are used.
31591898
Scanning the issue - special issue on real-time systems
30590203
Efficient State-Saving Architectures for Power-Mode Switching
Time and energy is expended in switching between power modes (e.g., active, hibernate, sleep, etc.). Powering off cache is one major reason for this. When there is a switch in the power-mode involving cache power-off, the system spends time and energy in filling the cache with new data (inherent cache misses). In our technique, before powering off the cache, we save its state in Embedded DRAM and bring it back when the previous power mode is restored. Our experiments have showed that in a majority of cases the cache contents are too valuable to be erased. By saving the contents we can reduce switching speed and energy. We present a heuristic to save the most relevant cache contents so that power and delay overheads are minimized. To measure the area overhead a synthesizable VHDL model was designed.
920212
Resource scheduling in dependable integrated modular avionics
In the recent development of avionics systems, integrated modular avionics (IMA) is advocated for next generation architecture that needs integration of mixed criticality real-time applications. These integrated applications meet their own timing constraints while sharing avionics computer resources. To guarantee timing constraints and dependability of each application, an IMA-based system is equipped with the schemes for spatial and temporal partitioning. We refer the model as SP-RTS (strongly partitioned real-time system), which deals with processor partitions and communication channels as its basic scheduling entities. This paper presents a partition and channel-scheduling algorithm for the SP-RTS. The basic idea of the algorithm is to use a two-level hierarchical schedule that activates partitions (or channels) following a distance-constraints guaranteed cyclic schedule and then dispatches tasks (or messages) according to a fixed priority schedule. To enhance schedulability, we devised heuristic algorithms for deadline decomposition and channel combining. The simulation results show the schedulability analysis of the two-level scheduling algorithm and the beneficial characteristics of the proposed deadline decomposition and channel combining algorithms.
40618061
Transaction Recovery in Distributed DB/DC Systems: A Progressive Approach
5961676
Total Data Quality Management: The Case of IRI
Abstract Implementing a Total Data Quality Management (TDQM) program is not a trivial undertaking. Two key steps are (1) to clearly define what an organization means by data quality and (2) to develop metrics that measure data quality dimensions and that are linked to the organization’s goals and objectives. This paper presents the case of Information Resources, Inc., which exemplifies how a company can develop a viable TDQM program.
14282973
Closing the Gap: Learning-Based Information Extraction Rivaling Knowledge-Engineering Methods
In this paper, we present a learning approach to the scenario template task of information extraction, where information filling one template could come from multiple sentences. When tested on the MUC-4 task, our learning approach achieves accuracy competitive to the best of the MUC-4 systems, which were all built with manually engineered rules. Our analysis reveals that our use of full parsing and state-of-the-art learning algorithms have contributed to the good performance. To our knowledge, this is the first research to have demonstrated that a learning approach to the full-scale information extraction task could achieve performance rivaling that of the knowledge engineering approach.
2908844
Operation-based Update Propagation in a Mobile File System
In this paper we describe a technique called operation-based update propagation for efficiently transmitting updates to large files that have been modified on a weakly connected client of a distributed file system. In this technique, modifications are captured above the file-system layer at the client, shipped to a surrogate client that is strongly connected to a server, re-executed at the surrogate, and the resulting files transmitted from the surrogate to the server. If re-execution fails to produce a file identical to the original, the system falls back to shipping the file from the client over the slow network. We have implemented a prototype of this mechanism in the Coda File System on Linux, and demonstrated performance improvements ranging from 40 percents to nearly three orders of magnitude in reduced network traffic and elapsed time. We also found a novel use of forward error correction in this context.
23745663
A filtering method for searching similar multidimensional sequences under the time-warping distance
The filtering method is currently the most suitable approach for the fast retrieval of similar sequences under the time-warping distance. Several filtering methods under the time-warping distance have been proposed, but they are only for real number sequences. This paper presents an efficient filtering method for the retrieval of similar multidimensional sequences. First, we propose three basic filtering measures (the end-point distance, the min-region distance, and the interim time-warping distance) based on the ones appeared in the literature, and one of their direct combinations (the point-region distance). Next, we investigate their problems with a large number of multidimensional sequences. In order to alleviate those problems, we extend the end-point distance and the min-region distance into the extended end-point distance and the segmented min-region distance, respectively, and combine them into a novel measure, the extended point-region distance. A multi-step architecture is adopted to implement the retrieval process with the proposed measure. Experiments with synthetic sequences are conducted for the performance comparison.
18483923
Network selection and discovery of service information in public WLAN hotspots
In a public WLAN hotspot, a roaming mobile terminal (MT) may be within radio range of more than one access point (AP), each of which may or may not have roaming agreements with the service provider of the user of the MT. In this case, the MT may need to discover some <i>service information</i> before it can make an intelligent <i>network-selection</i> decision. The most critical is <i>roaming information</i>; while other information such as <i>security policies</i>, <i>price</i>, <i>AP workload</i> may also be useful. Currently, roaming information is typically provisioned on the MTs as static <i>roaming tables</i> or <i>roaming lists</i>. However, this approach may not scale well when there are millions of hotspots globally. Addressing this shortcoming, recently several solutions have been proposed by different groups. In this paper, we contrast these solutions, and propose our own solution called <i>Roaming Information Code (RIC)</i>, which can be transported as SSID or a new Information Element of the 802.11 standard. RIC is scalable and can be fully backward compatible with existing APs (if transported as SSID). Furthermore, it does not hinder fast handoffs. In the second half of the paper, we will also discuss two other schemes addressing the other service information: a scheme called <i>RIC-VAP</i> for provider-specific security information; and a scheme that allows an AP to announce price and workload information.