| 1. |
- Afshar, Sara
(författare)
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Lock-Based Resource Sharing in Real-Time Multiprocessor Platforms
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Embedded systems are typically resource constrained, i.e., resources such as processors, I/O devices, shared buffers or shared memory can be limited for tasks in the system. Therefore, techniques that enable an efficient usage of such resources are of great importance.In the industry, typically large and complex software systems are divided into smaller parts (applications) where each part is developed independently. Migration towards multiprocessor platforms has become inevitable from an industrial perspective. Due to such migration and to efficient use of system resources, these applications eventually may be integrated on a shared multiprocessor platform. In order to facilitate the integration phase of the applications on a shared platform, the timing and resource requirements of each application can be provided in an interface when the application is developed. The system integrator can benefit from such provided information in the interface of each application to ease the integration process. In this thesis, we have provided the resource and timing requirements of each application in their interfaces for applications that may need several processors to be allocated on when they are developed.Although many scheduling techniques have been studied for multiprocessor systems, these techniques are usually based on the assumption that tasks are independent, i.e. do not share resources other than the processors. This assumption is typically not true. In this thesis, we provide an extension to such systems to handle sharing of resources other than processor among tasks. Two traditional approaches exist for multiprocessor systems to schedule tasks on processors. A recent scheduling approach for multiprocessors has combined the two traditional approaches and achieved a hybrid more efficient approach compared to the two previous one. Due to the complex nature of this scheduling approach the conventional approaches for resource sharing could not be used straight forwardly. In this thesis, we have modified resource sharing approaches such that they can be used in such hybrid scheduling systems. A second concern is that enabling resource sharing in the systems can cause unpredictable delays and variations in response time of tasks which can degrade system performance. Therefore, it is of great significance to improve the resource handling techniques to reduce the effect of imposed delays caused by resource sharing in a multiprocessor platform. In this thesis we have proposed alternative techniques for resource handling that can improve system performance for special setups.
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| 2. |
- Afshar, Sara, et al.
(författare)
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Per Processor Spin-Lock Priority for Partitioned Multiprocessor Real-Time Systems
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Two traditional approaches exist for a task that is blocked on a global resource; a task either performs a non-preemptive busy wait, i.e., spins, or suspends and releases the processor. Previously, we have shown that both approaches can be viewed as spinning either at the highest priority HP or at the lowest priority on the processor LP, respectively. Based on this view, previously we have generalized a task's blocking behavioral model, as spinning at any arbitrary priority level. In this paper, we focus on a particular class of spin-lock protocols from the introduced flexible spin-lock model where spinning is performed at a priority equal to or higher than the highest local ceiling of the global resources accessed on a processor referred to as CP spin-lock approach. In this paper, we assume that all tasks of a specific processor are spinning on the same priority level. Given this class and assumption, we show that there exists a spin-lock protocol in this range that dominates the classic spin-lock protocol which tasks spin on highest priority level (HP). However we show that this new approach is incomparable with the CP spin-lock approach. Moreover, we show that there may exist an intermediate spin-lock approach between the priority used by CP spin-lock approach and the new introduced spin-lock approach that can make a task set schedulable when those two cannot. We provide an extensive evaluation results comparing the HP, CP and the new proposed approach.
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| 3. |
- Afshar, Sara, et al.
(författare)
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Per Processor Spin-Lock Priority for Partitioned Multiprocessor Real-Time Systems
- 2017
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Ingår i: Leibniz Transactions on Embedded Systems. - 2199-2002. ; :2
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Two traditional approaches exist for a task that is blocked on a global resource; a task either performs a non-preemptive busy wait, i.e., spins, or suspends and releases the processor. Previously, we have shown that both approaches can be viewed as spinning either at the highest priority HP or at the lowest priority on the processor LP, respectively. Based on this view, previously we have generalized a task's blocking behavioral model, as spinning at any arbitrary priority level. In this paper, we focus on a particular class of spin-lock protocols from the introduced flexible spin-lock model where spinning is performed at a priority equal to or higher than the highest local ceiling of the global resources accessed on a processor referred to as CP spin-lock approach. In this paper, we assume that all tasks of a specific processor are spinning on the same priority level. Given this class and assumption, we show that there exists a spin-lock protocol in this range that dominates the classic spin-lock protocol which tasks spin on highest priority level (HP). However we show that this new approach is incomparable with the CP spin-lock approach. Moreover, we show that there may exist an intermediate spin-lock approach between the priority used by CP spin-lock approach and the new introduced spin-lock approach that can make a task set schedulable when those two cannot. We provide an extensive evaluation results comparing the HP, CP and the new proposed approach.
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| 4. |
- 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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| 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. |
- 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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| 7. |
- Imtiaz, Shamoona, et al.
(författare)
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Automatic Segmentation of Resource Utilization Data
- 2022
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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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| 8. |
- Jägemar, Marcus, 1972-
(författare)
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Utilizing Hardware Monitoring to Improve the Quality of Service and Performance of Industrial Systems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The drastically increased use of information and communications technology has resulted in a growing demand for telecommunication network capacity. The demand for radically increased network capacity coincides with industrial cost-reductions due to an increasingly competitive telecommunication market. We have addressed the capacity and cost-reduction problems in three ways.Our first contribution is a method to support shorter development cycles for new functionality and more powerful hardware. We reduce the development time by replicating the hardware usage of production systems in our test environment. Having a realistic test environment allows us to run performance tests at early design phases and therefore reducing the overall system development time.Our second contribution is a method to improve the communication performance through selective and automatic message compression. The message compression functionality monitors transmissions continuously and selects the most efficient compression algorithm. The message compression functionality evaluates several parameters such as network congestion level, CPU usage, and message content. Our implementation extends the communication capacity of a legacy communication API running on Linux where it emulates a legacy real-time operating system.In our third an final contribution, we implement a process allocation and scheduling framework to allow higher system performance and quality of service. The framework continuously monitors selected processes and correlate their performance to hardware usage such as caches, floating point unit and similar. The framework uses the performance-hardware correlation to minimize shared hardware resource congestion by efficiently allocate processes on multi-core CPUs. We have also designed a shared hardware resource aware process scheduler that makes it possible for multiple processes to co-exist on a CPU without affecting the performance of each other through hardware resource congestions. The allocation and scheduling techniques can be used to consolidate several functions on shared hardware thus reducing the system cost. We have implemented and evaluated our process scheduler as a new scheduling class in Linux.We have conducted several case studies in an industrial environment and verified all contributions in the scope of a large telecommunication system manufactured by Ericsson.%We have deployed all techniques in a complicated industrial legacy system with minimal impact. We show that we can provide a cost-effective solution, which is an essential requirement for industrial systems.
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| 9. |
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