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Documents authored by Skalistis, Stefanos

Document
DOI: 10.4230/LIPIcs.ECRTS.2020.4
Dynamic Interference-Sensitive Run-time Adaptation of Time-Triggered Schedules

Authors: Stefanos Skalistis and Angeliki Kritikakou

Published in: LIPIcs, Volume 165, 32nd Euromicro Conference on Real-Time Systems (ECRTS 2020)

Abstract
Over-approximated Worst-Case Execution Time (WCET) estimations for multi-cores lead to safe, but over-provisioned, systems and underutilized cores. To reduce WCET pessimism, interference-sensitive WCET (isWCET) estimations are used. Although they provide tighter WCET bounds, they are valid only for a specific schedule solution. Existing approaches have to maintain this isWCET schedule solution at run-time, via time-triggered execution, in order to be safe. Hence, any earlier execution of tasks, enabled by adapting the isWCET schedule solution, is not possible. In this paper, we present a dynamic approach that safely adapts isWCET schedules during execution, by relaxing or completely removing isWCET schedule dependencies, depending on the progress of each core. In this way, an earlier task execution is enabled, creating time slack that can be used by safety-critical and mixed-criticality systems to provide higher Quality-of-Services or execute other best-effort applications. The Response-Time Analysis (RTA) of the proposed approach is presented, showing that although the approach is dynamic, it is fully predictable with bounded WCET. To support our contribution, we evaluate the behavior and the scalability of the proposed approach for different application types and execution configurations on the 8-core Texas Instruments TMS320C6678 platform, obtaining significant performance improvements compared to static approaches.
Cite as

Stefanos Skalistis and Angeliki Kritikakou. Dynamic Interference-Sensitive Run-time Adaptation of Time-Triggered Schedules. In 32nd Euromicro Conference on Real-Time Systems (ECRTS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 165, pp. 4:1-4:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{skalistis_et_al:LIPIcs.ECRTS.2020.4,
  author =	{Skalistis, Stefanos and Kritikakou, Angeliki},
  title =	{{Dynamic Interference-Sensitive Run-time Adaptation of Time-Triggered Schedules}},
  booktitle =	{32nd Euromicro Conference on Real-Time Systems (ECRTS 2020)},
  pages =	{4:1--4:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-152-8},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{165},
  editor =	{V\"{o}lp, Marcus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2020.4},
  URN =		{urn:nbn:de:0030-drops-123673},
  doi =		{10.4230/LIPIcs.ECRTS.2020.4},
  annote =	{Keywords: Worst-Case Execution Time, Interference-sensitive, Run-time Adaptation, Time-Triggered, Response Time Analysis, Multi-cores}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2019.25
Hiding Communication Delays in Contention-Free Execution for SPM-Based Multi-Core Architectures

Authors: Benjamin Rouxel, Stefanos Skalistis, Steven Derrien, and Isabelle Puaut

Published in: LIPIcs, Volume 133, 31st Euromicro Conference on Real-Time Systems (ECRTS 2019)

Abstract
Multi-core systems using ScratchPad Memories (SPMs) are attractive architectures for executing time-critical embedded applications, because they provide both predictability and performance. In this paper, we propose a scheduling technique that jointly selects SPM contents off-line, in such a way that the cost of SPM loading/unloading is hidden. Communications are fragmented to augment hiding possibilities. Experimental results show the effectiveness of the proposed technique on streaming applications and synthetic task-graphs. The overlapping of communications with computations allows the length of generated schedules to be reduced by 4% on average on streaming applications, with a maximum of 16%, and by 8% on average for synthetic task graphs. We further show on a case study that generated schedules can be implemented with low overhead on a predictable multi-core architecture (Kalray MPPA).
Cite as

Benjamin Rouxel, Stefanos Skalistis, Steven Derrien, and Isabelle Puaut. Hiding Communication Delays in Contention-Free Execution for SPM-Based Multi-Core Architectures. In 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 133, pp. 25:1-25:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{rouxel_et_al:LIPIcs.ECRTS.2019.25,
  author =	{Rouxel, Benjamin and Skalistis, Stefanos and Derrien, Steven and Puaut, Isabelle},
  title =	{{Hiding Communication Delays in Contention-Free Execution for SPM-Based Multi-Core Architectures}},
  booktitle =	{31st Euromicro Conference on Real-Time Systems (ECRTS 2019)},
  pages =	{25:1--25:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-110-8},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{133},
  editor =	{Quinton, Sophie},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2019.25},
  URN =		{urn:nbn:de:0030-drops-107626},
  doi =		{10.4230/LIPIcs.ECRTS.2019.25},
  annote =	{Keywords: Real-time Systems, Contention-Free Scheduling, SPM multi-core architecture}
}
Document
DOI: 10.4230/OASIcs.MCPS.2014.66
Modeling of Reconfigurable Medical Ultrasonic Applications in BIP

Authors: Stefanos Skalistis and Alena Simalatsar

Published in: OASIcs, Volume 36, 5th Workshop on Medical Cyber-Physical Systems (2014)

Abstract
Medical ultrasonic imaging applications require high quality of images produced in real-time often with limited resources available. Deadlock-freedom and confluency must be guaranteed to ensure the correctness of the applications, while feasibility and optimality properties are required to provide the best Quality of Service (QoS) within available resources. In this paper we introduce BIP (Behavior-Interaction-Priority) framework components as main building blocks to model such applications in a correct-by-construction manner. Based on those components we model a reconfigurable multi-mode processing pipeline for ultrasonic imaging that supports QoS management by topology reconfiguration. Finally, as a proof of concept, we present a simple quality controller as a well-triggered component, which when combined with the processing pipeline can manipulate the quality of image processing.
Cite as

Stefanos Skalistis and Alena Simalatsar. Modeling of Reconfigurable Medical Ultrasonic Applications in BIP. In 5th Workshop on Medical Cyber-Physical Systems. Open Access Series in Informatics (OASIcs), Volume 36, pp. 66-79, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{skalistis_et_al:OASIcs.MCPS.2014.66,
  author =	{Skalistis, Stefanos and Simalatsar, Alena},
  title =	{{Modeling of Reconfigurable Medical Ultrasonic Applications in BIP}},
  booktitle =	{5th Workshop on Medical Cyber-Physical Systems},
  pages =	{66--79},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-66-8},
  ISSN =	{2190-6807},
  year =	{2014},
  volume =	{36},
  editor =	{Turau, Volker and Kwiatkowska, Marta and Mangharam, Rahul and Weyer, Christoph},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.MCPS.2014.66},
  URN =		{urn:nbn:de:0030-drops-45246},
  doi =		{10.4230/OASIcs.MCPS.2014.66},
  annote =	{Keywords: Reconfigurable Pipelines, Quality of Service, Medical Ultrasonic Applications, Component-based System Design, Behavior-Interaction-Priority Modal Flow}
}
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