4,257 research outputs found
Performance Analysis of Modified SRPT in Multiple-Processor Multitask Scheduling
In this paper we study the multiple-processor multitask scheduling problem in
both deterministic and stochastic models. We consider and analyze Modified
Shortest Remaining Processing Time (M-SRPT) scheduling algorithm, a simple
modification of SRPT, which always schedules jobs according to SRPT whenever
possible, while processes tasks in an arbitrary order. The M-SRPT algorithm is
proved to achieve a competitive ratio of for
minimizing response time, where denotes the ratio between maximum job
workload and minimum job workload, represents the ratio between maximum
non-preemptive task workload and minimum job workload. In addition, the
competitive ratio achieved is shown to be optimal (up to a constant factor),
when there are constant number of machines. We further consider the problem
under Poisson arrival and general workload distribution (\ie, system),
and show that M-SRPT achieves asymptotic optimal mean response time when the
traffic intensity approaches , if job size distribution has finite
support. Beyond finite job workload, the asymptotic optimality of M-SRPT also
holds for infinite job size distributions with certain probabilistic
assumptions, for example, system with finite task workload
Restart-Based Fault-Tolerance: System Design and Schedulability Analysis
Embedded systems in safety-critical environments are continuously required to
deliver more performance and functionality, while expected to provide verified
safety guarantees. Nonetheless, platform-wide software verification (required
for safety) is often expensive. Therefore, design methods that enable
utilization of components such as real-time operating systems (RTOS), without
requiring their correctness to guarantee safety, is necessary.
In this paper, we propose a design approach to deploy safe-by-design embedded
systems. To attain this goal, we rely on a small core of verified software to
handle faults in applications and RTOS and recover from them while ensuring
that timing constraints of safety-critical tasks are always satisfied. Faults
are detected by monitoring the application timing and fault-recovery is
achieved via full platform restart and software reload, enabled by the short
restart time of embedded systems. Schedulability analysis is used to ensure
that the timing constraints of critical plant control tasks are always
satisfied in spite of faults and consequent restarts. We derive schedulability
results for four restart-tolerant task models. We use a simulator to evaluate
and compare the performance of the considered scheduling models
Preemptive scheduling on uniform parallel machines with controllable job processing times
In this paper, we provide a unified approach to solving preemptive scheduling problems with uniform parallel machines and controllable processing times. We demonstrate that a single criterion problem of minimizing total compression cost subject to the constraint that all due dates should be met can be formulated in terms of maximizing a linear function over a generalized polymatroid. This justifies applicability of the greedy approach and allows us to develop fast algorithms for solving the problem with arbitrary release and due dates as well as its special case with zero release dates and a common due date. For the bicriteria counterpart of the latter problem we develop an efficient algorithm that constructs the trade-off curve for minimizing the compression cost and the makespan
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