| 1. |
- Behnam, Moris
(författare)
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Hierarchical Real Time Scheduling and Synchronization
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)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, et al.
(författare)
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Overrun Methods for Semi-Independent Real-Time Hierarchical Scheduling
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Hierarchical Scheduling Framework (HSF) has been introduced as a design-time framework to enable compositional schedulability analysis of embedded software systems with real-time properties. In this paper a software system consists of a number of semi-independent components called subsystems. Subsystems are developed independently and later integrated to form a system. To support this design process, in the paper, the proposed methods allow non-intrusive configuration and tuning of subsystem timing-behaviour via subsystem interfaces for selecting scheduling parameters. This paper considers three methods to handle overruns due to resource sharing between subsystems in the HSF. For each one of these three overrun methods corresponding scheduling algorithms The work in this paper is supported by the Swedish Foundation for Strategic Research (SSF), via the research programme PROGRESS. and associated schedulability analysis are presented together with analysis that shows under what circumstances one or the other is preferred. The analysis is generalized to allow for both Fixed Priority Scheduling (FPS) and Earliest Deadline First (EDF) scheduling. Also, a further contribution of the paper is the technique of calculating resource-holding times within the framework under different scheduling algorithms. The resource holding times being an important parameter in the global schedulability analysis.
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| 3. |
- Behnam, Moris, et al.
(författare)
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SIRAP: A Global Resource Sharing Protocol Facilitating Integration of Semi-independent Real-Time Systems
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a protocol for resource sharing in a hierarchical real-time scheduling framework. Together, the protocol and the scheduling framework significantly reduce the efforts and errors associated with integrating multiple semi-independent subsystems on a single processor. Thus, our proposed techniques facilitate modern software development processes, where subsystems are developed by independent teams (or subcontractors) and at a later stage integrated into a single product. Using our solution, a subsystem need not know, and is not dependent on, the timing behaviour of other subsystems; even though they share mutually exclusive resources. In this paper we also prove the correctness of our approach and evaluate its efficiency.
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| 4. |
- 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/konstnärligt)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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| 5. |
- Danielsson, Jakob
(författare)
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Automatic Characterization and Mitigation of Shared-resource Contention in Multi-core Systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multi-core computers are infamous for being hard to use in time-critical systems due to execution-time variations as an effect of shared resource contention. In this thesis, we study the problem of shared resource contention, which occurs when multiple applications executing on different cores do not have exclusive access to of a shared hardware resource. We investigate performance variations of parallel tasks in multi-core systems and present a method to pinpoint the source of the resource contention using hardware performance counters. We investigate mitigation methods for performance variations due to resource contention, including the Jailhouse hypervisor and the cache-partitioning tool PALLOC. We propose a benchmark strategy that quantifies the isolation gained from a specific isolation technique and exemplify this strategy using the Jailhouse hypervisor. We furthermore present and implement solutions for cache-partition allocation during application runtime. Our implementation aims to avoid over-provisioning of cache through pre-runtime estimations of an application's dependency towards the cache and continuous re-partitioning of the cache memory during application runtime.The primary goal of this thesis is to contribute to a process that automates some of the tedious manual testing needed to detect resource contention bottlenecks. The methods we present in this provide a holistic solution for automatic mitigating resource-contention in a multi-core system. First, we evaluate the risk for shared resource contention when several applications execute simultaneously. We then allocate partitions to mitigate resource contention for applications that risk severe performance degradations. We finally present methods that dynamically re-allocate partition space to meet the performance requirements of the running applications.
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| 6. |
- Inam, Rafia, 1974-
(författare)
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Hierarchical scheduling for predictable execution of real-time software components and legacy systems
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents techniques to achieve predictable execution of coarse-grained software components and for preservation of temporal properties of components during their integration and reuse.The dissertation presents a novel concept runnable virtual node (RVN) which interaction with the environment is bounded both by a functional and a temporal interface, and the validity of its internal temporal behaviour is preserved when integrated with other components or when reused in a new environment. The realization of RVN exploits techniques for hierarchical scheduling to achieve temporal isolation, and the principles from component-based software-engineering to achieve functional isolation. The proof-of-concept case studies executed on a micro-controller demonstrate the preserving of real-time properties within software components for predictable integration and reusability in a new environment, in both hierarchical scheduling and RVN contexts.Further, a multi-resource server (MRS) is proposed and implemented to enable predictable execution when composing multiple real-time components on a COTS multicore platform. MRS uses resource reservation for both CPU-bandwidth and memory-bus bandwidth to bound the interferences between tasks running on the same core, as well as, between tasks running on different cores. The later could, without MRS, interfere with each other due to contention on a shared memory-bus and memory. The results indicated that MRS can be used to "encapsulate" legacy systems and to give them enough resources to fulfill their purpose. In the dissertation, the compositional schedulability analysis for MRS is also provided and an experimental study is performed to bring insight on the correlation between the server budgets.We believe that the proposed approaches enable a faster software integration and support legacy reuse and that this work transcend the boundaries of software engineering and real-time systems.
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| 7. |
- Shin, Insik, et al.
(författare)
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On Optimal Hierarchical Resource Sharing in Open Environments
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a new perspective in the context of supporting logical resource sharing under hierarchical scheduling. Our work is motivated from a tradeoff between reducing resource holding times and reducing system load (i.e., the collective processor requirements to guarantee the schedulability of hierarchical scheduling frameworks). We formulate an optimization problem that determines the resource holding times of each individual tasks (and therefore those of subsystems) with the goal of minimizing the system load subject to the system's schedulability. We present efficient algorithms to find an optimal solution to the problem, and we prove their correctness.
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| 8. |
- Tsog, Nandinbaatar
(författare)
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Space Computing using COTS Heterogeneous Platforms : Intelligent On-Board Data Processing in Space Systems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Space computing enriches space activities such as deep-space explorations and in-orbit intelligent decision making. The awareness of space computing is growing due to the technological advances of high-performance commercial off-the-shelf (COTS) computing platforms. Space offers a complex, constrained and challengeable environment to the developers, researchers, as well as human beings. The challenges are size, weight and power (SWaP) constraints, real-time requirements, communication limitations as well as radiation effects. The research conducted in this thesis aims at investigating and supporting intelligent on-board data processing using COTS heterogeneous computing platforms in space systems. These platforms embed at least one Central Processing Unit (CPU) and one Graphics Processing Unit (GPU) on the same chip. The main goal of the research presented in this thesis is twofold. First, to investigate the heterogeneous computing platforms for the purpose of proposing a solution to tackle the above-mentioned challenges in space systems. Second, to complement the proposed solution with novel scheduling techniques for real-time applications that run on COTS heterogeneous platforms under harsh environments like space.The proposed techniques are based on the system model that considers the use of alternative executions of parallel segments of tasks. Although offloading a parallel segment to a parallel computation unit (such as GPU) improves the best-case execution times of most applications, it can increase the response times of tasks in some applications due to the overuse of GPU. Hence, the use of the proposed task model can be a key to decrease the response times of tasks and improve schedulability of the system. The server-based proposed scheduling techniques support the proposed task model by guaranteeing the execution slot for parallel segments on CPU(s). The experimental evaluation conducted in this thesis shows that the proposed task model can improve the schedulability of the real-time systems up to 90% with the static allocation of applications. Moreover, the dynamic allocation method using the server-based scheduling with the proposed task model can improve the schedulability up to 16%. Finally, the thesis presents a simulation tool that simulates real-time applications using the proposed task model while considering the different levels of radiation tolerance to different processing units.
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