In an effort to promote the use of Ada in embedded system development, a realistic avionics application model whose hard real-time properties are fully predictable has been generated. This was done starting with a rate monotonic analysis of a set of typical fully synchronized periodic and aperiodic avionics tasks drawn from an idealized attack aircraft mission computer. The authors describe this avionics case study and its goals, examine the resulting design issues and trade-offs, and investigate the ability of the rate monotonic analysis model to predict its performance under a heavy load.<<ETX>>

[IEEE Comput. Soc. Press Twelfth Real-Time Systems Symposium - San Antonio, TX, USA (4-6 Dec. 1991)] [1991] Proceedings Twelfth Real-Time Systems Symposium - Building a predictable avionics platform in Ada: a case study

In real-time applications, the computer is often required to service programs in response to external signals, and to guarantee that each such program is completely processed within a specified interval following the occurrence of the initiating signal. Such programs are referred to in this paper as time-critical processes, or TCPs.

Scheduling of time critical processes

The present invention proposes a disk array apparatus that can dramatically enhance its operability. The disk array apparatus has a source volume that is the source for data migration, and migrates the data to a destination volume that is the destination for the data migration. The disk array apparatus includes: an access frequency calculator for calculating the frequency of access to the source volume for each time period of a certain length of time going back from a data migration termination date and time when the data migration termination date and time is designated externally; an estimated data migration amount calculator for calculating the estimated data migration amount for each time period based on the access frequency calculated by the access frequency calculator; and a data migration start date and time calculator for calculating the data migration start date and time based on the estimated data migration amount calculated by the estimated data migration amount calculator.

Disk array apparatus, data migration method, and storage medium

A system transforms data structures absent the need for a backup copy. The system transforms a first logical store in an initial logical arrangement to a desired logical arrangement where the data structures of the logical arrangements are different. The system uses a select sequence of data operations that moves data from its origin in the initial logical arrangement to a target location in the desired logical arrangement. The system generates and properly locates parity information when so desired. The system executes a subsequent data operation in accordance with an indication that the previous data operation was successful. Each subsequent data operation uses the source location from the previous data operation. A non-volatile memory element holds information concerning a present data operation to enable a rollback operation when a present data operation is unsuccessful.

RAID Converter and Methods for Transforming a First RAID Array to a Second RAID Array Without Creating a Backup Copy

A method, system, apparatus, and computer-readable medium are provided for storing data at a virtual tape library (“VTL”) computer or server. According to one method, a VTL computer maintains one or more storage volumes for use by initiators on an array of mass storage devices. Space on each of the volumes is allocated using thin provisioning. The VTL computer may also include a cache memory that is at least the size of a full stripe of the array. Write requests received at the VTL computer are stored in the cache memory until a full stripe of data has been received. Once a full stripe of data has been received, the full stripe of data is written to the array at once. The array utilized by the VTL computer may include a hot spare mass storage device. When a failed mass storage device is identified, only the portions of the failed device that have been previously written are rebuilt onto the hot spare. The array may be maintained using RAID-5. If one of the mass storage devices in the array fails, any subsequent writes directed to the array may be stored using RAID-0.

Performance in virtual tape libraries

Functional Reactive Programming (FRP) is a declarative approach for modeling and building reactive systems. The FRP has been shown to be an expressive formalism for building graphics, robotic, and vision applications. The Priority-based FRP (P-FRP) is a formalism of FRP that allows preemption of execution and guarantees real-time response. Since functional programs cannot maintain state and mutable data, changes made by programs that are preempted have to be rolled back, and the work done by the preempted programs has to be discarded. Hence in the P-FRP model, a preempted lower priority task will have to restart after higher priority tasks have completed execution. Current real-time research mainly focuses on the classic preemptive or non-preemptive models and plenty methods have been developed to analyze the real-time guarantees of these models. Unfortunately, due to its transactional nature where preempted tasks are aborted and have to restart, the execution semantics of the P-FRP model does not fit into the standard definitions of classic preemptive or non-preemptive execution. In this survey paper, we review existing researches on the P-FRP task scheduling, and present a few research areas for future work.

P-FRP task scheduling: A survey

The concept of feasibility (or schedulability) interval plays a very important role in the schedulability analysis in real-time systems. Existing results on the schedulability testing interval of real-time task sets under fixed priority scheduling with arbitrary release offsets (or phases) have limitations for certain scenarios in constructing a schedule for testing the schedulability of a given task set. In this paper, we propose a transforming method for deriving minimal schedulability testing interval of real-time n-task sets with arbitrary release offsets under fixed priority scheduling in both the classical pre-emptive model and the Priority-based Functional Reactive Programming (P-FRP) model on uniprocessor. The complexity of our transforming method is O(n), and the validity is also proved by theoretical analysis.

Minimal Schedulability Testing Interval for Real-Time Periodic Tasks with Arbitrary Release Offsets

This paper studies the schedulability of real-time tasks in the Priority-based Functional Reactive Programming (P-FRP) model under fixed priority scheduling, one of the influential scheduling policies. Since the abort-and-restart execution paradigm of the P-FRP model is different from that of the classic pre-emptive model, the schedulability analysis for P-FRP tasks under fixed priority scheduling differs widely. In P-FRP, for a synchronous n-task set under fixed priority scheduling, the least common multiple (LCM) of all n task periods is the typical length of a testing interval for an exact (necessary and sufficient) schedulability test. In this paper, we propose and prove an optimal simulation based exact schedulability test in the P-FRP model under fixed priority scheduling for a given priority order, covering scenarios from synchronous task release to asynchronous task release with the initial busy condition, and from implicit deadlines to constrained deadlines. The length of a testing interval for the exact test is the LCM of the first n-1 task periods and its optimality is proved.

Schedulability Analysis for Real-Time P-FRP Tasks under Fixed Priority Scheduling

Reducing job migrations is essential for any global multiprocessor scheduling algorithm. In this letter, we present a global, dynamic-priority, laxity-based algorithm that reduces the number of migrations on multiprocessor embedded systems by leveraging information theory principles. A simplification of the proposed scheduling theory is presented to reduce the overhead caused by using information theory. Our results show that the proposed algorithm is able to reduce the number of migrations by up to 41.21% when compared with other global, dynamic-priority, laxity-based algorithms. As the utilization per task set and the number of processors increase, simplified information-theoretic scheduling algorithm is able to improve its performance in terms of the number of migrations.

Real-Time Multiprocessor Scheduling Algorithm Based on Information Theory Principles

Method and related apparatus for data migration of a disk array. While striping and migrating data of a source disk of the disk array, data stripes are grouped into different zones; after completely writing data stripes of a given zone to disks of the disk array, data stripes of next zone are written to disks of the disk array and the given zone. Because data stripes of the next zone will be distributed to various disks, only some of the data stripes will overwrite data stripes of the given zone. Therefore, the next zone can contain more data stripes than the given zone while keeping migration integration. In addition, by zones containing increasing number of data stripes, migration progress can be managed with ease and high efficiency achieving better data throughput.

Xingliang Zou

Papers

P-FRP task scheduling: A survey

Minimal Schedulability Testing Interval for Real-Time Periodic Tasks with Arbitrary Release Offsets

Schedulability Analysis for Real-Time P-FRP Tasks under Fixed Priority Scheduling

Real-Time Multiprocessor Scheduling Algorithm Based on Information Theory Principles

Method and related apparatus for data migration utilizing disk arrays