| 11. |
- 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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| 12. |
- Behnam, Moris, et al.
(författare)
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Real-Time Control Design for Flexible Scheduling using Jitter Margin
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Real-time control algorithms are designed based on the characteristics of the controlled plants and they require good performance without delays. However, digital control implementation typically introduces delays and jitters due to insufficient CPU processing power and the limitations of the real-time scheduling method used. This can degrade the system performance or even make it unstable. In this paper we propose an integrated approach for control design and real-time scheduling, suitable for both discrete-time and continuous-time controllers. It guarantees system performance by accepting a certain minimum value of jitter for control tasks and feasibly schedules them together with other tasks in the system. Results from comparison with other approaches from real-time and control theory domains underline the effectiveness of our method.
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| 13. |
- Behnam, Moris, 1973-, et al.
(författare)
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Schedulability analysis of synchronization protocols based on overrun without payback for hierarchical scheduling frameworks revisited
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we show that both global as well as local schedulability analysis of synchronization protocols based on the stack resource protocol (SRP) and overrun without payback for hierarchical scheduling frameworks based on fixed-priority pre-emptive scheduling (FPPS) are pessimistic.We present improved global and local schedulability analysis,illustrate the improvements by means of examples, and show that the improved global analysis is both uniform and sustainable.We evaluate the improved global and local schedulabilityanalysis based on an extensive simulation study and comparethe results with the existing analysis.
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| 14. |
- 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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| 15. |
- 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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| 16. |
- 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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| 17. |
- Ferko, Enxhi, et al.
(författare)
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Investigating interoperability in Digital Twin Architectures.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Digital Twin architectures comprise multi-integrated building blocks, which include components for data acquisition, management, and processing. Effective and error-prone data exchange between building blocks of the digital twin is the foundation of its successful implementation reflecting the growing importance of interoperability (i.e. ability of systems to exchange data and make use of the data that is exchanged). This paper examines communication technologies (such as protocols and standards) used for the development of digital twins for manufacturing identifying interfaces between physical counterparts and digital twins, as well as between different digital twins, with the ultimate goal of analysing data interoperability concerns. At this end, we use the assessment model “Levels of Conceptual Interoperability Model” to define the applicable levels of interoperability for the identified interfaces and discuss the trade-offs for reaching higher levels of interoperability.
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| 18. |
- Ferko, Enxhi
(författare)
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Towards a Standards-Based Architecture for Digital Twins Facilitating Interoperability
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Digital transformation is rapidly changing the business landscape, compellingcompanies to invest in it due to its several benefits, such as reduced time-to-value, improved quality, and the ability to overcome hardware limitations. Aprominent technology enabling digital transformation is digital twin. A digitaltwin is a virtual representation of a physical asset, system, or process, usedfor monitoring and controlling purposes. Implementing digital twins requirestackling challenging engineering tasks such as establishing accurate digitalrepresentations of physical systems or ensuring live data synchronization. Suchchallenges are exacerbated by a lack of research on software architecturesthat meet required quality attributes, their actual implementation, and otherengineering tasks. Software architectures serve as a blueprint and foundationfor building software-intensive systems that meet specific requirements. Theyprovide a comprehensive overview of a system components, their properties,and relationships. Reference architectures, which are based on establishedbest practices in a given domain, help in reasoning about a class of softwarearchitectures and facilitate the engineering of software-intensive systems such asdigital twins. Given the above premises, the ultimate goal of this research is todefine a standard-based reference architecture for digital twins in manufacturingto improve interoperability. We use existing standards as common ground tofacilitate technology transfer between academia and industry. In addition, wefocus on interoperability as it is a crucial quality attribute affecting the functionalsuitability and performance efficiency of digital twins.
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| 19. |
- Imtiaz, Shamoona
(författare)
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Automated Performance Profiling of Software Applications
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For industrial systems performance, it is desired to keep the IT infrastructure competitive through the efficient use of computer resources. However, modern software applications are complex and often utilize a broad spectrum of available hardware resources. The way how applications utilize these resources may vary from platform to platform due to the different architectural features, requirements and performance levels guaranteed by the hardware as well as due to the type of application under analysis. It becomes challenging to predict how the deployed applications will perform on a particular platform, how to improve the hardware resource utilization, and how to meet the Quality of Service (QoS) requirements. Computers these days enable us to precisely trace down the performance of applications using the Performance Monitoring Counters (PMCs) available in the Performance Monitoring Unit (PMU) of the processors. PMCs can record micro-architectural events, called PMU events, at the CPU cycle level. Tools like perf API and PAPI provide performance information using manual and selective function calls. Nevertheless, it is difficult for humans to make analyses, visualize performance over time and draw conclusions from this wealth of data without automatic and intelligent tools. In this thesis, our first contribution is to propose a cross-platform automated approach to investigate the overall performance profile of the applications. Instead of relying on a static and pre-selected list of hardware and software performance events we avoid the selection bias by capturing the entire range of performance events specific to the platform on which applications are running. The performance data being generated from shared resource environments and hierarchical resource utilization demands makes it harder to represent the behavior in one model. That being the case, it was deemed appropriate to demonstrate the compact representation of behavior. So, our next contribution is to present a simplified model to understand the behavior of performance events. Therefore, we determine segments in performance data by locating the points in their data distribution using the change point detection method. The proposed solution reduces the complexity of data handling, allows the application of further statistical analyses and provides better visualization. Lastly, to reveal the out-of-sight information, we present a customized approach to automatically identify the groups of similar performance events based on the change in their behavior. There can be several ways to group the performance data, we opt to form the groups based on change points in the behavior of the performance events. The knowledge can then be used by the decision-makers as per their interests such as for load balancing, deployments, scheduling and anomalous behavior detection.
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| 20. |
- Imtiaz, Shamoona, et al.
(författare)
-
Automatic Segmentation of Resource Utilization Data
- 2022
-
Ingår i: 1st IEEE Industrial Electronics Society Annual On-Line Conference (ONCON) 2022. - 9798350398069
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Advancement of industrial systems seek improvements to achieve required level of quality of service and efficient performance management. It is essential though to have better understanding of resource utilization behaviour of applications in execution. Even the expert engineers desire to envision dependencies and impact of one computer resource on the other. For such situations it is significant to know statistical relationship between data sets such as a resource with higher cache demand should not be scheduled together with other cache hungry process at the same time and same core. Performance monitoring data coming from hardware and software is huge and grouping of this time series data based on similar behaviour can display distinguishable execution phases. For benefits like these we opt to choose change point analysis method. By using this method study determined the optimal threshold which can identify more or less same segments for other executions of same application and same event. These segments are then validated with the help of test data. Finally the study provided segment-wise, local, compact statistical model with decent accuracy.
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