34159049
Approximation algorithms for scheduling real-time jobs with multiple feasible intervals
Time-critical jobs in many real-time applications have multiple feasible intervals. Such a job is constrained to execute from start to completion in one of its feasible intervals. A job fails if the job remains incomplete at the end of the last feasible interval. Earlier works developed an optimal off-line algorithm to schedule all the jobs in a given job set and on-line heuristics to schedule the jobs in a best effort manner. This paper is concerned with how to find a schedule in which the number of jobs completed in one of their feasible intervals is maximized. We show that the maximization problem is $${\cal N}{\cal P}$$-hard for both non-preemptible and preemptible jobs. This paper develops two approximation algorithms for non-preemptible and preemptible jobs. When jobs are non-preemptible, Algorithm Least Earliest Completion Time First (LECF) is shown to have a 2-approximation factor; when jobs are preemptible, Algorithm Least Execution Time First (LEF) is proved being a 3-approximation algorithm. We show that our analysis for the two algorithms are tight. We also evaluate our algorithms by extensive simulations. Simulation results show that Algorithms LECF and LEF not only guarantee the approximation factors but also outperform other multiple feasible interval scheduling algorithms in average.
12533129
Procrastination for leakage-aware rate-monotonic scheduling on a dynamic voltage scaling processor
As the dynamic voltage scaling (DVS) technique provides system engineers the flexibility to trade-off the performance and the energy consumption, DVS has been adopted in many computing systems. However, the longer a job executes, the more energy in the leakage current the device/processor consumes for the job. To reduce the energy consumption resulting from the leakage current, a system might enter the dormant mode. This paper targets energy-efficient rate-monotonic scheduling for periodic real-time tasks on a uniprocessor DVS system with non-negligible leakage power consumption. An on-line simulated scheduling strategy and a virtually blocking time strategy are developed for procrastination scheduling to reduce energy consumption. The proposed algorithms derive a feasible schedule for real-time tasks with worst-case guarantees for any input instance. Experimental results show that our proposed algorithms could derive energy-efficient solutions.
30973700
Allocation cost minimization for periodic hard real-time tasks in energy-constrained DVS systems
5871408
Leakage-Aware Energy-Efficient Scheduling of Real-Time Tasks in Multiprocessor Systems
This work targets energy-efficient scheduling of periodic real-time tasks over multiple DVS processors with the considerations of power consumption due to leakage current. A polynomial-time algorithm with a 1.283 approximation bound is proposed when the overheads in turning on/off a processor are negligible. When the overheads are non-negligible, we develop polynomial-time algorithms with a 2 approximation bound. A series of simulation experiments was done for the performance evaluation of the proposed algorithms. The simulation results show that the proposed algorithms could derive schedules very close to optimal solutions.
17449226
Approximation algorithms for scheduling multiple feasible interval jobs
Time-critical jobs in many real-time applications have multiple feasible intervals. Such a job is constrained to execute from start to completion in one of its feasible intervals. A job fails if the job remains incomplete at the end of the last feasible interval. This paper is concerned with how to find a schedule in which the number of jobs completed in one of their feasible intervals is maximized. We show that the maximization problem is NP-hard for both nonpreemptible and preemptible jobs. This paper develops two approximation algorithms for nonpreemptible and preemptible jobs. When jobs are nonpreemptible, algorithm LECF is with a 2-approximation factor; when jobs are preemptible, algorithm LEF is proved being a 3-approximation algorithm. We also show that our analysis on the two algorithms is tight by providing a set of input instances. Simulation results demonstrate that algorithms LECF and LEF not only guarantee the approximation factors but also outperform other multiple feasible interval scheduling algorithms.
27587317
An executable specification language for specification understanding in object-oriented specification reuse
System analysis time can be reduced through specification reuse which, however, requires specification understanding. This paper presents an object-oriented executable specification language which reduces understanding time through executing specifications. In addition to being executable, the specification language hides as many classes as possible within subsystems, and explicitly specifies relationships between specification components. This facilitates specification modification. Moreover, the language explicitly specifies interface parameters of specification components. This facilitates specification composition.
46388294
Soft Sorting in Logic Programming
Integrating sorts (types) into logic programming languages increases their expressiveness and evaluation efficiency. The sort structures usually considered are strict, in the sense that whenever an expression has a subexpression which is not properly sorted, the expression is classified as ill-sorted, and in effect is regarded as meaningless. Typically a logic programming language with strict sorting is incomplete, in the sense that some intuitively meaningful programs and queries are ill-sorted and hence are not part of the language.
2221913
A Simple Linear-Time Approximation Algorithm for Multi-processor Job Scheduling on Four Processors
Multiprocessor job scheduling problem has become increasingly interesting, for both theoretical study and practical applications. Theoretical study of the problem has made significant progress recently, which, however, seems not to imply practical algorithms for the problem, yet. Practical algorithms have been developed only for systems with three processors and the techniques seem difficult to extend to systems with more than three processors. This paper offers new observations and introduces new techniques for the multiprocessor job scheduling problem on systems with four processors. A very simple and practical linear time approximation algorithm of ratio bounded by 1:5 is developed for the multi-processor job scheduling problem P4|fix|Cmax, which significantly improves previous results. Our techniques are also useful for multiprocessor job scheduling problems on systems with more than four processors.
2426986
Quantifying Privacy Leakage through Answering Database Queries
We assume a database consists of records of individuals with private or sensitive fields. Queries on the distribution of a sensitive field within a selected population in the database can be submitted to the data center. The answers to the queries leak private information of individuals though no identification information is provided. Inspired by decision theory, we present a quantitative model for the privacy protection problem in such a database query or linkage environment in this paper. In the model, the value of information is estimated from the viewpoint of the querier.To estimate the value, we define the information state of the data user by a class of probability distributions on the set of possible confidential values. We further define the usefulness of information based on how easy the data user can locate individuals that fit the description given in the queries. These states and the usefulness of information can be modified and refined by the user's knowledge acquisition actions. The value of information is then defined as the expected gain of the privacy receiver and the privacy is protected by imposing costs on the answers of the queries for balancing the gain.
47173629
A Polynomial Time Approximation Scheme for General Multiprocessor Job Scheduling
Recently, there have been considerable interests in the multiprocessor job scheduling problem, in which a job can be processed in parallel on one of several alternative subsets of processors. In this paper, a polynomial time approximation scheme is presented for the problem in which the number of processors in the system is a fixed constant. This result is the best possible because of the strong NP-hardness of the problem and is a significant improvement over the past results: the best previous result was an approximation algorithm of ratio $7/6 + \epsilon$ for 3-processor systems based on Goemans's algorithm for a restricted version of the problem.