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Documents authored by Bletsas, Konstantinos

Document
DOI: 10.4230/LIPIcs.ECRTS.2018.2
Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers

Authors: Muhammad Ali Awan, Pedro F. Souto, Konstantinos Bletsas, Benny Akesson, and Eduardo Tovar

Published in: LIPIcs, Volume 106, 30th Euromicro Conference on Real-Time Systems (ECRTS 2018)

Abstract
In multicore architectures, there is potential for contention between cores when accessing shared resources, such as system memory. Such contention scenarios are challenging to accurately analyse, from a worst-case timing perspective. One way of making memory contention in multicores more amenable to timing analysis is the use of memory regulation mechanisms. It restricts the number of accesses performed by any given core over time by using periodically replenished per-core budgets. Typically, this assumes that all cores access memory via a single shared memory controller. However, ever-increasing bandwidth requirements have brought about architectures with multiple memory controllers. These control accesses to different memory regions and are potentially shared among all cores. While this presents an opportunity to satisfy bandwidth requirements, existing analysis designed for a single memory controller are no longer safe. This work formulates a worst-case memory stall analysis for a memory-regulated multicore with two memory controllers. This stall analysis can be integrated into the schedulability analysis of systems under fixed-priority partitioned scheduling. Five heuristics for assigning tasks and memory budgets to cores in a stall-cognisant manner are also proposed. We experimentally quantify the cost in terms of extra stall for letting all cores benefit from the memory space offered by both controllers, and also evaluate the five heuristics for different system characteristics.
Cite as

Muhammad Ali Awan, Pedro F. Souto, Konstantinos Bletsas, Benny Akesson, and Eduardo Tovar. Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 2:1-2:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{awan_et_al:LIPIcs.ECRTS.2018.2,
  author =	{Awan, Muhammad Ali and Souto, Pedro F. and Bletsas, Konstantinos and Akesson, Benny and Tovar, Eduardo},
  title =	{{Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{2:1--2:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-075-0},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{106},
  editor =	{Altmeyer, Sebastian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2018.2},
  URN =		{urn:nbn:de:0030-drops-90025},
  doi =		{10.4230/LIPIcs.ECRTS.2018.2},
  annote =	{Keywords: multiple memory controllers, memory regulation, multicore}
}
Document
DOI: 10.4230/DARTS.4.2.5
Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers (Artifact)

Authors: Muhammad Ali Awan, Pedro F. Souto, Konstantinos Bletsas, Benny Akesson, and Eduardo Tovar

Published in: DARTS, Volume 4, Issue 2, Special Issue of the 30th Euromicro Conference on Real-Time Systems (ECRTS 2018)

Abstract
This artifact demonstrates the performance of the proposed worst-case memory stall analysis for a memory-regulated multicore with two memory controllers. The memory stall analysis is implemented in Java along with five different stall-cognisant bandwidth-to-core and task-to-core assignment heuristics. It evaluates the performance of these heuristics in terms of schedulability via experiments with synthetic task sets capturing different system characteristics. It also quantifies the cost in terms of extra stall for letting all cores benefit from the memory space offered by both controllers on the given multicore platform.
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Muhammad Ali Awan, Pedro F. Souto, Konstantinos Bletsas, Benny Akesson, and Eduardo Tovar. Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers (Artifact). In Special Issue of the 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Dagstuhl Artifacts Series (DARTS), Volume 4, Issue 2, pp. 5:1-5:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{awan_et_al:DARTS.4.2.5,
  author =	{Awan, Muhammad Ali and Souto, Pedro F. and Bletsas, Konstantinos and Akesson, Benny and Tovar, Eduardo},
  title =	{{Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers (Artifact)}},
  pages =	{5:1--5:3},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2018},
  volume =	{4},
  number =	{2},
  editor =	{Awan, Muhammad Ali and Souto, Pedro F. and Bletsas, Konstantinos and Akesson, Benny and Tovar, Eduardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.4.2.5},
  URN =		{urn:nbn:de:0030-drops-89732},
  doi =		{10.4230/DARTS.4.2.5},
  annote =	{Keywords: multiple memory controllers, memory regulation, multicore}
}
Document
DOI: 10.4230/LITES-v005-i001-a002
Errata for Three Papers (2004-05) on Fixed-Priority Scheduling with Self-Suspensions

Authors: Konstantinos Bletsas, Neil C. Audsley, Wen-Hung Huang, Jian-Jia Chen, and Geoffrey Nelissen

Published in: LITES, Volume 5, Issue 1 (2018). Leibniz Transactions on Embedded Systems, Volume 5, Issue 1

Abstract
The purpose of this article is to (i) highlight the flaws in three previously published works [Audsley, 2004a; Audsley, 2004b; Bletsas, 2005] on the worst-case response time analysis for tasks with self-suspensions and (ii) provide straightforward fixes for those flaws, hence rendering the analysis safe.
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Konstantinos Bletsas, Neil C. Audsley, Wen-Hung Huang, Jian-Jia Chen, and Geoffrey Nelissen. Errata for Three Papers (2004-05) on Fixed-Priority Scheduling with Self-Suspensions. In LITES, Volume 5, Issue 1 (2018). Leibniz Transactions on Embedded Systems, Volume 5, Issue 1, pp. 02:1-02:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{bletsas_et_al:LITES-v005-i001-a002,
  author =	{Bletsas, Konstantinos and Audsley, Neil C. and Huang, Wen-Hung and Chen, Jian-Jia and Nelissen, Geoffrey},
  title =	{{Errata for Three Papers (2004-05) on Fixed-Priority Scheduling with Self-Suspensions}},
  journal =	{Leibniz Transactions on Embedded Systems},
  pages =	{02:1--02:20},
  ISSN =	{2199-2002},
  year =	{2018},
  volume =	{5},
  number =	{1},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LITES-v005-i001-a002},
  doi =		{10.4230/LITES-v005-i001-a002},
  annote =	{Keywords: real-time, scheduling, self-suspension, worst-case response time analysis}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2017.18
Mixed-Criticality Scheduling with Dynamic Redistribution of Shared Cache

Authors: Muhammad Ali Awan, Konstantinos Bletsas, Pedro F. Souto, Benny Akesson, and Eduardo Tovar

Published in: LIPIcs, Volume 76, 29th Euromicro Conference on Real-Time Systems (ECRTS 2017)

Abstract
The design of mixed-criticality systems often involves painful tradeoffs between safety guarantees and performance. However, the use of more detailed architectural models in the design and analysis of scheduling arrangements for mixed-criticality systems can provide greater confidence in the analysis, but also opportunities for better performance. Motivated by this view, we propose an extension of Vestal's model for mixed-criticality multicore systems that (i) accounts for the per-task partitioning of the last-level cache and (ii) supports the dynamic reassignment, for better schedulability, of cache portions initially reserved for lower-criticality tasks to the higher-criticality tasks, when the system switches to high-criticality mode. To this model, we apply partitioned EDF scheduling with Ekberg and Yi's deadline-scaling technique. Our schedulability analysis and scalefactor calculation is cognisant of the cache resources assigned to each task, by using WCET estimates that take into account these resources. It is hence able to leverage the dynamic reconfiguration of the cache partitioning, at mode change, for better performance, in terms of provable schedulability. We also propose heuristics for partitioning the cache in low- and high-criticality mode, that promote schedulability. Our experiments with synthetic task sets, indicate tangible improvements in schedulability compared to a baseline cache-aware arrangement where there is no redistribution of cache resources from low- to high-criticality tasks in the event of a mode change.
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Muhammad Ali Awan, Konstantinos Bletsas, Pedro F. Souto, Benny Akesson, and Eduardo Tovar. Mixed-Criticality Scheduling with Dynamic Redistribution of Shared Cache. In 29th Euromicro Conference on Real-Time Systems (ECRTS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 76, pp. 18:1-18:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{awan_et_al:LIPIcs.ECRTS.2017.18,
  author =	{Awan, Muhammad Ali and Bletsas, Konstantinos and Souto, Pedro F. and Akesson, Benny and Tovar, Eduardo},
  title =	{{Mixed-Criticality Scheduling with Dynamic Redistribution of Shared Cache}},
  booktitle =	{29th Euromicro Conference on Real-Time Systems (ECRTS 2017)},
  pages =	{18:1--18:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-037-8},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{76},
  editor =	{Bertogna, Marko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2017.18},
  URN =		{urn:nbn:de:0030-drops-71710},
  doi =		{10.4230/LIPIcs.ECRTS.2017.18},
  annote =	{Keywords: Mixed Criticality Scheduling, Vestal Model, Dynamic Redistribution of Shared Cache, Shared Last-level Cache Analysis, Cache-aware Scheduling}
}
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