| 1. |
- Behnam, Moris
(författare)
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Hierarchical Real Time Scheduling and Synchronization
- 2008
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Licentiatavhandling (övrigt vetenskapligt)abstract
- The Hierarchical Scheduling Framework (HSF) has been introduced to enable compositional schedulability analysis and execution of embedded software systems with real-time constraints. In this thesis, we consider a system consisting of a number of semi-independent components called subsystems, and these subsystems are allowed to share logical resources. The HSF provides CPU-time to the subsystems and it guarantees that the individual subsystems respect their allocated CPU budgets. However, if subsystems are allowed to share logical resources, extra complexity with respect to analysis and run-time mechanisms is introduced. In this thesis we address three issues related to hierarchical scheduling of semi-independent subsystems. In the first part, we investigate the feasibility of implementing the hierarchical scheduling framework in a commercial operating system, and we present the detailed figures of various key properties with respect to the overhead of the implementation.In the second part, we studied the problem of supporting shared resources in a hierarchical scheduling framework and we propose two different solutions to support resource sharing. The first proposed solution is called SIRAP, a synchronization protocol for resource sharing in hierarchically scheduled open real-time systems, and the second solution is an enhanced overrun mechanism.In the third part, we present a resource efficient approach to minimize system load (i.e., the collective CPU requirements to guarantee the schedulability of hierarchically scheduled subsystems). Our work is motivated from a tradeoff between reducing resource locking times and reducing system load. We formulate an optimization problem that determines the resource locking times of each individual subsystem with the goal of minimizing the system load subject to system schedulability. We present linear complexity algorithms to find an optimal solution to the problem, and we prove their correctness
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| 2. |
- Behnam, Moris, 1973-
(författare)
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Synchronization Protocols for a Compositional Real-Time Scheduling Framework
- 2010
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Doktorsavhandling (övrigt vetenskapligt)abstract
- In this thesis we propose techniques to simplify the integration of subsystems while minimizing the overall amount of CPU resources needed to guarantee the schedulability of real-time tasks. In addition, we provide solutions to the problem of allowing for the use of logical resources requiring mutual exclusion.The contribution of the thesis is presented in three parts. In the first part, we propose a synchronization protocol, called SIRAP, to facilitate sharing of logical resources in a hierarchical scheduling framework. In addition, we extend an existing synchronization protocol, called HSRP, such that each subsystem can be developed independently. The performance of the proposed protocols is evaluated by extensive simulations. In the second part, we present an efficient schedulability analysis that exploits the lower scheduling overhead introduced by each of the proposed protocols. Finally, in the third part, we propose new methods and algorithms that find the optimal system parameters (e.g., optimal resource ceiling), that minimize the amount of CPU resources required to ensure schedulability, when using the proposed synchronization protocols in a hierarchical scheduling framework.The motivation of this work comes from an emerging industrial trend in embedded software systems development to integrate multiple applications (subsystems) on a small number of processors. The purpose of this integration is to reduce the hardware related costs as well as the communication complexity between processors. In this setting a large number of industrial applications face the problem of preserving their real-time properties after their integration onto a single processor. In addition, temporal isolation between the applications during runtime may be required to prevent failure propagation between different applications.Specifically, we propose a hierarchical scheduling framework that allows for a simplified integration of subsystems. The framework preserves the essential temporal characteristics of the subsystems, both when running in isolation as well as when they are integrated with other subsystems. In this thesis, we assume a model where a system consists of a number of subsystems. The subsystems can interact with each other using shared logical resources. The framework ensures that the individual subsystem respects its allocated share of the processor. The difficulty lies in allowing two or more subsystems to share logical resources, which introduces an additional complexity in the schedulability analysis and also increases the system load.
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| 3. |
- Behnam, Moris, et al.
(författare)
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Towards Hierarchical Scheduling in VxWorks
- 2008
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Ingår i: OSPERT 2008, Proceedings of the Fourth International Workshop on Operating Systems Platforms for Embedded Real-Time Applications. ; s. 63-72
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Konferensbidrag (refereegranskat)abstract
- Over the years, we have worked on hierarchical schedulingframeworks from a theoretical point of view. In thispaper we present our initial results of the implementationof our hierarchical scheduling framework in a commercialoperating system VxWorks. The purpose of the implementationis twofold: (1) we would like to demonstrate feasibilityof its implementation in a commercial operating system,without having to modify the kernel source code, and (2) wewould like to present detailed figures of various key propertieswith respect to the overhead of the implementation.During the implementation of the hierarchical scheduler,we have also developed a number of simple task schedulers.We present details of the implementation of Rate-Monotonic(RM) and Earliest Deadline First (EDF) schedulers. Finally,we present the design of our hierarchical schedulingframework, and we discuss our current status in the project.
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| 4. |
- Inam, Rafia, 1974-, et al.
(författare)
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Hard Real-time Support for Hierarchical Scheduling in FreeRTOS
- 2011
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Ingår i: Proceedings of 7th annual workshop on Operating Systems Platforms for Embedded Real-Time Applications July 5th, 2011 in Porto, Portugal : in conjunction with the23rd Euromicro Conference on Real-Time SystemsPortugal, July 6-8, 201. ; s. 51-60
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Konferensbidrag (refereegranskat)abstract
- This paper presents extensions to the previous implementationof two-level Hierarchical Scheduling Framework(HSF) for FreeRTOS. The results presented here allow the useof HSF for FreeRTOS in hard-real time applications, with thepossibility to include legacy applications and components notexplicitly developed for hard real-time or the HSF.Specifically, we present the implementations of (i) global andlocal resource sharing using the Hierarchical Stack ResourcePolicy and Stack Resource Policy respectively, (ii) kernel supportfor the periodic task model, and (iii) mapping of original FreeRTOSAPI to the extended FreeRTOS HSF API. We also presentevaluations of overheads and behavior for different alternativeimplementations of HSRP with overrun from experiments on theAVR 32-bit board EVK1100. In addition, real-time schedulinganalysis with models of the overheads of our implementation ispresented.
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| 5. |
- Nemati, Farhang, et al.
(författare)
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Blocking-Aware Partitioning for Multiprocessors
- 2010
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Rapport (övrigt vetenskapligt)abstract
- In the multi-core and multiprocessor domain there are two scheduling approaches, global and partitioned scheduling. Under global scheduling each task can execute on any processor while under partitioned scheduling tasks are allocated to processors and migration of tasks among processors is not allowed. Under global scheduling the higher utilization bound can be achieved, but in practice the overheads of migrating tasks is high. On the other hand, besides simplicity and efficiency of partitioned scheduling protocols, existing scheduling and synchronization methods developed for uniprocessor platforms can more easily be extended to partitioned scheduling. This also simplifies migration of existing systems to multi-cores. An important issue related to partitioned scheduling is how to distribute tasks among processors/cores to increase performance offered by the platform. However, existing methods mostly assume independent tasks while in practice a typical real-time system contains tasks that share resources and they may block each other. In this paper we propose a blocking-aware partitioning algorithm to distribute tasks onto different processors. The proposed algorithm allocates a task set onto processors in a way that blocking times of tasks are decreased. This reduces the total utilization which has the potential to decrease the total number of needed processors/cores.
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