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Documents authored by Chen, Jian-Jia

Document
DOI: 10.4230/LIPIcs.ECRTS.2023.10
On the Equivalence of Maximum Reaction Time and Maximum Data Age for Cause-Effect Chains

Authors: Mario Günzel, Harun Teper, Kuan-Hsun Chen, Georg von der Brüggen, and Jian-Jia Chen

Published in: LIPIcs, Volume 262, 35th Euromicro Conference on Real-Time Systems (ECRTS 2023)

Abstract
Real-time systems require a formal guarantee of timing-constraints, not only for individual tasks but also for data-propagation. The timing behavior of data-propagation paths in a given system is typically described by its maximum reaction time and its maximum data age. This paper shows that they are equivalent. To reach this conclusion, partitioned job chains are introduced, which consist of one immediate forward and one immediate backward job chain. Such partitioned job chains are proven to describe maximum reaction time and maximum data age in a universal manner. This universal description does not only show the equivalence of maximum reaction time and maximum data age, but can also be exploited to speed up the computation of such significantly. In particular, the speed-up for synthesized task sets based on automotive benchmarks can be up to 1600. Since only very few non-restrictive assumptions are made, the equivalence of maximum data age and maximum reaction time holds for almost any scheduling mechanism and even for tasks which do not adhere to the typical periodic or sporadic task model. This observation is supported by a simulation of a ROS2 navigation system.
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Mario Günzel, Harun Teper, Kuan-Hsun Chen, Georg von der Brüggen, and Jian-Jia Chen. On the Equivalence of Maximum Reaction Time and Maximum Data Age for Cause-Effect Chains. In 35th Euromicro Conference on Real-Time Systems (ECRTS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 262, pp. 10:1-10:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{gunzel_et_al:LIPIcs.ECRTS.2023.10,
  author =	{G\"{u}nzel, Mario and Teper, Harun and Chen, Kuan-Hsun and von der Br\"{u}ggen, Georg and Chen, Jian-Jia},
  title =	{{On the Equivalence of Maximum Reaction Time and Maximum Data Age for Cause-Effect Chains}},
  booktitle =	{35th Euromicro Conference on Real-Time Systems (ECRTS 2023)},
  pages =	{10:1--10:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-280-8},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{262},
  editor =	{Papadopoulos, Alessandro V.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2023.10},
  URN =		{urn:nbn:de:0030-drops-180392},
  doi =		{10.4230/LIPIcs.ECRTS.2023.10},
  annote =	{Keywords: End-to-End, Timing Analysis, Maximum Data Age, Maximum Reaction Time, Cause-Effect Chain, Robot Operating Systems 2 (ROS2)}
}
Document
DOI: 10.4230/OASIcs.WCET.2022.2
LLVMTA: An LLVM-Based WCET Analysis Tool

Authors: Sebastian Hahn, Michael Jacobs, Nils Hölscher, Kuan-Hsun Chen, Jian-Jia Chen, and Jan Reineke

Published in: OASIcs, Volume 103, 20th International Workshop on Worst-Case Execution Time Analysis (WCET 2022)

Abstract
We present llvmta, an academic WCET analysis tool based on the LLVM compiler infrastructure. It aims to enable the evaluation of novel WCET analysis approaches in a state-of-the-art analysis framework without dealing with the complexity of modeling real-world hardware architectures. We discuss the main design decisions and interfaces that allow to implement new analysis approaches. Finally, we highlight various existing research projects whose evaluation has been enabled by llvmta.
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Sebastian Hahn, Michael Jacobs, Nils Hölscher, Kuan-Hsun Chen, Jian-Jia Chen, and Jan Reineke. LLVMTA: An LLVM-Based WCET Analysis Tool. In 20th International Workshop on Worst-Case Execution Time Analysis (WCET 2022). Open Access Series in Informatics (OASIcs), Volume 103, pp. 2:1-2:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{hahn_et_al:OASIcs.WCET.2022.2,
  author =	{Hahn, Sebastian and Jacobs, Michael and H\"{o}lscher, Nils and Chen, Kuan-Hsun and Chen, Jian-Jia and Reineke, Jan},
  title =	{{LLVMTA: An LLVM-Based WCET Analysis Tool}},
  booktitle =	{20th International Workshop on Worst-Case Execution Time Analysis (WCET 2022)},
  pages =	{2:1--2:17},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-244-0},
  ISSN =	{2190-6807},
  year =	{2022},
  volume =	{103},
  editor =	{Ballabriga, Cl\'{e}ment},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2022.2},
  URN =		{urn:nbn:de:0030-drops-166242},
  doi =		{10.4230/OASIcs.WCET.2022.2},
  annote =	{Keywords: WCET analysis, low-level analysis, LLVM}
}
Document
Artifact
DOI: 10.4230/DARTS.8.1.2
Unikernel-Based Real-Time Virtualization Under Deferrable Servers: Analysis and Realization (Artifact)

Authors: Kuan-Hsun Chen, Mario Günzel, Boguslaw Jablkowski, Markus Buschhoff, and Jian-Jia Chen

Published in: DARTS, Volume 8, Issue 1, Special Issue of the 34th Euromicro Conference on Real-Time Systems (ECRTS 2022)

Abstract
This artifact provides the source code to validate and reproduce the numerical results of the associated paper "Unikernel-Based Real-Time Virtualization under Deferrable Servers: Analysis and Realization". Due to the nature of a close-source project with the company, i.e., EMVICORE GmbH, the source code of the case study in Section 6.2 is not included in this artifact.
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Kuan-Hsun Chen, Mario Günzel, Boguslaw Jablkowski, Markus Buschhoff, and Jian-Jia Chen. Unikernel-Based Real-Time Virtualization Under Deferrable Servers: Analysis and Realization (Artifact). In Special Issue of the 34th Euromicro Conference on Real-Time Systems (ECRTS 2022). Dagstuhl Artifacts Series (DARTS), Volume 8, Issue 1, pp. 2:1-2:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{chen_et_al:DARTS.8.1.2,
  author =	{Chen, Kuan-Hsun and G\"{u}nzel, Mario and Jablkowski, Boguslaw and Buschhoff, Markus and Chen, Jian-Jia},
  title =	{{Unikernel-Based Real-Time Virtualization Under Deferrable Servers: Analysis and Realization (Artifact)}},
  pages =	{2:1--2:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2022},
  volume =	{8},
  number =	{1},
  editor =	{Chen, Kuan-Hsun and G\"{u}nzel, Mario and Jablkowski, Boguslaw and Buschhoff, Markus and Chen, Jian-Jia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DARTS.8.1.2},
  URN =		{urn:nbn:de:0030-drops-164987},
  doi =		{10.4230/DARTS.8.1.2},
  annote =	{Keywords: Unikernel, Virtualization, Reservation Servers, Deferrable Servers, Cyber-Physical Systems, Real-Time Systems}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2022.6
Unikernel-Based Real-Time Virtualization Under Deferrable Servers: Analysis and Realization

Authors: Kuan-Hsun Chen, Mario Günzel, Boguslaw Jablkowski, Markus Buschhoff, and Jian-Jia Chen

Published in: LIPIcs, Volume 231, 34th Euromicro Conference on Real-Time Systems (ECRTS 2022)

Abstract
For cyber-physical systems, real-time virtualization optimizes the hardware utilization by consolidating multiple systems into the same platform, while satisfying the timing constraints of their real-time tasks. This paper considers virtualization based on unikernels, i.e., single address space kernels usually constructed by using library operating systems. Each unikernel is a guest operating system in the virtualization and hosts a single real-time task. We consider deferrable servers in the virtualization platform to schedule the unikernel-based guest operating systems and analyze the worst-case response time of a sporadic real-time task under such a virtualization architecture. Throughout synthesized tasksets, we empirically show that our analysis outperforms the restated analysis derived from the state-of-the-art, which is based on Real-Time Calculus. Furthermore, we provide insights on implementation-specific issues and offer evidence that the proposed scheduling architecture can be effectively implemented on top of the Xen hypervisor while incurring acceptable overhead.
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Kuan-Hsun Chen, Mario Günzel, Boguslaw Jablkowski, Markus Buschhoff, and Jian-Jia Chen. Unikernel-Based Real-Time Virtualization Under Deferrable Servers: Analysis and Realization. In 34th Euromicro Conference on Real-Time Systems (ECRTS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 231, pp. 6:1-6:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{chen_et_al:LIPIcs.ECRTS.2022.6,
  author =	{Chen, Kuan-Hsun and G\"{u}nzel, Mario and Jablkowski, Boguslaw and Buschhoff, Markus and Chen, Jian-Jia},
  title =	{{Unikernel-Based Real-Time Virtualization Under Deferrable Servers: Analysis and Realization}},
  booktitle =	{34th Euromicro Conference on Real-Time Systems (ECRTS 2022)},
  pages =	{6:1--6:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-239-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{231},
  editor =	{Maggio, Martina},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2022.6},
  URN =		{urn:nbn:de:0030-drops-163239},
  doi =		{10.4230/LIPIcs.ECRTS.2022.6},
  annote =	{Keywords: Unikernel, Virtualization, Reservation Servers, Deferrable Servers, Cyber-Physical Systems, Real-Time Systems}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2021.10
Hard Real-Time Stationary GANG-Scheduling

Authors: Niklas Ueter, Mario Günzel, Georg von der Brüggen, and Jian-Jia Chen

Published in: LIPIcs, Volume 196, 33rd Euromicro Conference on Real-Time Systems (ECRTS 2021)

Abstract
The scheduling of parallel real-time tasks enables the efficient utilization of modern multiprocessor platforms for systems with real-time constrains. In this situation, the gang task model, in which each parallel sub-job has to be executed simultaneously, has shown significant performance benefits due to reduced context switches and more efficient intra-task synchronization. In this paper, we provide the first schedulability analysis for sporadic constrained-deadline gang task systems and propose a novel stationary gang scheduling algorithm. We show that the schedulability problem of gang task sets can be reduced to the uniprocessor self-suspension schedulability problem. Furthermore, we provide a class of partitioning algorithms to find a stationary gang assignment and show that it bounds the worst-case interference of each task. To demonstrate the effectiveness of our proposed approach, we evaluate it for implicit-deadline systems using randomized task sets under different settings, showing that our approach outperforms the state-of-the-art.
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Niklas Ueter, Mario Günzel, Georg von der Brüggen, and Jian-Jia Chen. Hard Real-Time Stationary GANG-Scheduling. In 33rd Euromicro Conference on Real-Time Systems (ECRTS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 196, pp. 10:1-10:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{ueter_et_al:LIPIcs.ECRTS.2021.10,
  author =	{Ueter, Niklas and G\"{u}nzel, Mario and von der Br\"{u}ggen, Georg and Chen, Jian-Jia},
  title =	{{Hard Real-Time Stationary GANG-Scheduling}},
  booktitle =	{33rd Euromicro Conference on Real-Time Systems (ECRTS 2021)},
  pages =	{10:1--10:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-192-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{196},
  editor =	{Brandenburg, Bj\"{o}rn B.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2021.10},
  URN =		{urn:nbn:de:0030-drops-139410},
  doi =		{10.4230/LIPIcs.ECRTS.2021.10},
  annote =	{Keywords: Real-Time Systems, Gang Scheduling, Parallel Computing, Scheduling Algorithms}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2020.18
Offloading Safety- and Mission-Critical Tasks via Unreliable Connections

Authors: Lea Schönberger, Georg von der Brüggen, Kuan-Hsun Chen, Benjamin Sliwa, Hazem Youssef, Aswin Karthik Ramachandran Venkatapathy, Christian Wietfeld, Michael ten Hompel, and Jian-Jia Chen

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

Abstract
For many cyber-physical systems, e.g., IoT systems and autonomous vehicles, offloading workload to auxiliary processing units has become crucial. However, since this approach highly depends on network connectivity and responsiveness, typically only non-critical tasks are offloaded, which have less strict timing requirements than critical tasks. In this work, we provide two protocols allowing to offload critical and non-critical tasks likewise, while providing different service levels for non-critical tasks in the event of an unsuccessful offloading operation, depending on the respective system requirements. We analyze the worst-case timing behavior of the local cyber-physical system and, based on these analyses, we provide a sufficient schedulability test for each of the proposed protocols. In the course of comprehensive experiments, we show that our protocols have reasonable acceptance ratios under the provided schedulability tests. Moreover, we demonstrate that the system behavior under our proposed protocols is strongly dependent on probability of unsuccessful offloading operations, the percentage of critical tasks in the system, and the amount of offloaded workload.
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Lea Schönberger, Georg von der Brüggen, Kuan-Hsun Chen, Benjamin Sliwa, Hazem Youssef, Aswin Karthik Ramachandran Venkatapathy, Christian Wietfeld, Michael ten Hompel, and Jian-Jia Chen. Offloading Safety- and Mission-Critical Tasks via Unreliable Connections. In 32nd Euromicro Conference on Real-Time Systems (ECRTS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 165, pp. 18:1-18:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{schonberger_et_al:LIPIcs.ECRTS.2020.18,
  author =	{Sch\"{o}nberger, Lea and von der Br\"{u}ggen, Georg and Chen, Kuan-Hsun and Sliwa, Benjamin and Youssef, Hazem and Ramachandran Venkatapathy, Aswin Karthik and Wietfeld, Christian and ten Hompel, Michael and Chen, Jian-Jia},
  title =	{{Offloading Safety- and Mission-Critical Tasks via Unreliable Connections}},
  booktitle =	{32nd Euromicro Conference on Real-Time Systems (ECRTS 2020)},
  pages =	{18:1--18:22},
  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.2020.18},
  URN =		{urn:nbn:de:0030-drops-123811},
  doi =		{10.4230/LIPIcs.ECRTS.2020.18},
  annote =	{Keywords: internet of things, cyber-physical systems, real-time, mixed-criticality, self-suspension, computation offloading, scheduling, communication}
}
Document
Artifact
DOI: 10.4230/DARTS.5.1.6
Scheduling Self-Suspending Tasks: New and Old Results (Artifact)

Authors: Jian-Jia Chen, Tobias Hahn, Ruben Hoeksma, Nicole Megow, and Georg von der Brüggen

Published in: DARTS, Volume 5, Issue 1, Special Issue of the 31st Euromicro Conference on Real-Time Systems (ECRTS 2019)

Abstract
In computing systems, a job may suspend itself (before it finishes its execution) when it has to wait for certain results from other (usually external) activities. For real-time systems, such self-suspension behavior has been shown to induce performance degradation. Hence, the researchers in the real-time systems community have devoted themselves to the design and analysis of scheduling algorithms that can alleviate the performance penalty due to self-suspension behavior. As self-suspension and delegation of parts of a job to non-bottleneck resources is pretty natural in many applications, researchers in the operations research (OR) community have also explored scheduling algorithms for systems with such suspension behavior, called the master-slave problem in the OR community. This paper first reviews the results for the master-slave problem in the OR literature and explains their impact on several long-standing problems for scheduling self-suspending real-time tasks. For frame-based periodic real-time tasks, in which the periods of all tasks are identical and all jobs related to one frame are released synchronously, we explore different approximation metrics with respect to resource augmentation factors under different scenarios for both uniprocessor and multiprocessor systems, and demonstrate that different approximation metrics can create different levels of difficulty for the approximation. Our experimental results show that such more carefully designed schedules can significantly outperform the state-of-the-art.
Cite as

Jian-Jia Chen, Tobias Hahn, Ruben Hoeksma, Nicole Megow, and Georg von der Brüggen. Scheduling Self-Suspending Tasks: New and Old Results (Artifact). In Special Issue of the 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Dagstuhl Artifacts Series (DARTS), Volume 5, Issue 1, pp. 6:1-6:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@Article{chen_et_al:DARTS.5.1.6,
  author =	{Chen, Jian-Jia and Hahn, Tobias and Hoeksma, Ruben and Megow, Nicole and von der Br\"{u}ggen, Georg},
  title =	{{Scheduling Self-Suspending Tasks: New and Old Results}},
  pages =	{6:1--6:3},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2019},
  volume =	{5},
  number =	{1},
  editor =	{Chen, Jian-Jia and Hahn, Tobias and Hoeksma, Ruben and Megow, Nicole and von der Br\"{u}ggen, Georg},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DARTS.5.1.6},
  URN =		{urn:nbn:de:0030-drops-107349},
  doi =		{10.4230/DARTS.5.1.6},
  annote =	{Keywords: Self-suspension, master-slave problem, computational complexity, speedup factors}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2019.16
Scheduling Self-Suspending Tasks: New and Old Results

Authors: Jian-Jia Chen, Tobias Hahn, Ruben Hoeksma, Nicole Megow, and Georg von der Brüggen

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

Abstract
In computing systems, a job may suspend itself (before it finishes its execution) when it has to wait for certain results from other (usually external) activities. For real-time systems, such self-suspension behavior has been shown to induce performance degradation. Hence, the researchers in the real-time systems community have devoted themselves to the design and analysis of scheduling algorithms that can alleviate the performance penalty due to self-suspension behavior. As self-suspension and delegation of parts of a job to non-bottleneck resources is pretty natural in many applications, researchers in the operations research (OR) community have also explored scheduling algorithms for systems with such suspension behavior, called the master-slave problem in the OR community. This paper first reviews the results for the master-slave problem in the OR literature and explains their impact on several long-standing problems for scheduling self-suspending real-time tasks. For frame-based periodic real-time tasks, in which the periods of all tasks are identical and all jobs related to one frame are released synchronously, we explore different approximation metrics with respect to resource augmentation factors under different scenarios for both uniprocessor and multiprocessor systems, and demonstrate that different approximation metrics can create different levels of difficulty for the approximation. Our experimental results show that such more carefully designed schedules can significantly outperform the state-of-the-art.
Cite as

Jian-Jia Chen, Tobias Hahn, Ruben Hoeksma, Nicole Megow, and Georg von der Brüggen. Scheduling Self-Suspending Tasks: New and Old Results. In 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 133, pp. 16:1-16:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{chen_et_al:LIPIcs.ECRTS.2019.16,
  author =	{Chen, Jian-Jia and Hahn, Tobias and Hoeksma, Ruben and Megow, Nicole and von der Br\"{u}ggen, Georg},
  title =	{{Scheduling Self-Suspending Tasks: New and Old Results}},
  booktitle =	{31st Euromicro Conference on Real-Time Systems (ECRTS 2019)},
  pages =	{16:1--16:23},
  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.2019.16},
  URN =		{urn:nbn:de:0030-drops-107532},
  doi =		{10.4230/LIPIcs.ECRTS.2019.16},
  annote =	{Keywords: Self-suspension, master-slave problem, computational complexity, speedup factors}
}
Document
DOI: 10.4230/LIPIcs.ISAAC.2018.71
Packing Sporadic Real-Time Tasks on Identical Multiprocessor Systems

Authors: Jian-Jia Chen, Nikhil Bansal, Samarjit Chakraborty, and Georg von der Brüggen

Published in: LIPIcs, Volume 123, 29th International Symposium on Algorithms and Computation (ISAAC 2018)

Abstract
In real-time systems, in addition to the functional correctness recurrent tasks must fulfill timing constraints to ensure the correct behavior of the system. Partitioned scheduling is widely used in real-time systems, i.e., the tasks are statically assigned onto processors while ensuring that all timing constraints are met. The decision version of the problem, which is to check whether the deadline constraints of tasks can be satisfied on a given number of identical processors, has been known NP-complete in the strong sense. Several studies on this problem are based on approximations involving resource augmentation, i.e., speeding up individual processors. This paper studies another type of resource augmentation by allocating additional processors, a topic that has not been explored until recently. We provide polynomial-time algorithms and analysis, in which the approximation factors are dependent upon the input instances. Specifically, the factors are related to the maximum ratio of the period to the relative deadline of a task in the given task set. We also show that these algorithms unfortunately cannot achieve a constant approximation factor for general cases. Furthermore, we prove that the problem does not admit any asymptotic polynomial-time approximation scheme (APTAS) unless P=NP when the task set has constrained deadlines, i.e., the relative deadline of a task is no more than the period of the task.
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Jian-Jia Chen, Nikhil Bansal, Samarjit Chakraborty, and Georg von der Brüggen. Packing Sporadic Real-Time Tasks on Identical Multiprocessor Systems. In 29th International Symposium on Algorithms and Computation (ISAAC 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 123, pp. 71:1-71:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{chen_et_al:LIPIcs.ISAAC.2018.71,
  author =	{Chen, Jian-Jia and Bansal, Nikhil and Chakraborty, Samarjit and von der Br\"{u}ggen, Georg},
  title =	{{Packing Sporadic Real-Time Tasks on Identical Multiprocessor Systems}},
  booktitle =	{29th International Symposium on Algorithms and Computation (ISAAC 2018)},
  pages =	{71:1--71:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-094-1},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{123},
  editor =	{Hsu, Wen-Lian and Lee, Der-Tsai and Liao, Chung-Shou},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2018.71},
  URN =		{urn:nbn:de:0030-drops-100198},
  doi =		{10.4230/LIPIcs.ISAAC.2018.71},
  annote =	{Keywords: multiprocessor partitioned scheduling, approximation factors}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2018.6
Efficiently Approximating the Probability of Deadline Misses in Real-Time Systems

Authors: Georg von der Brüggen, Nico Piatkowski, Kuan-Hsun Chen, Jian-Jia Chen, and Katharina Morik

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

Abstract
This paper explores the probability of deadline misses for a set of constrained-deadline sporadic soft real-time tasks on uniprocessor platforms. We explore two directions to evaluate the probability whether a job of the task under analysis can finish its execution at (or before) a testing time point t. One approach is based on analytical upper bounds that can be efficiently computed in polynomial time at the price of precision loss for each testing point, derived from the well-known Hoeffding's inequality and the well-known Bernstein's inequality. Another approach convolutes the probability efficiently over multinomial distributions, exploiting a series of state space reduction techniques, i.e., pruning without any loss of precision, and approximations via unifying equivalent classes with a bounded loss of precision. We demonstrate the effectiveness of our approaches in a series of evaluations. Distinct from the convolution-based methods in the literature, which suffer from the high computation demand and are applicable only to task sets with a few tasks, our approaches can scale reasonably without losing much precision in terms of the derived probability of deadline misses.
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Georg von der Brüggen, Nico Piatkowski, Kuan-Hsun Chen, Jian-Jia Chen, and Katharina Morik. Efficiently Approximating the Probability of Deadline Misses in Real-Time Systems. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 6:1-6:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{vonderbruggen_et_al:LIPIcs.ECRTS.2018.6,
  author =	{von der Br\"{u}ggen, Georg and Piatkowski, Nico and Chen, Kuan-Hsun and Chen, Jian-Jia and Morik, Katharina},
  title =	{{Efficiently Approximating the Probability of Deadline Misses in Real-Time Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{6:1--6:22},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2018.6},
  URN =		{urn:nbn:de:0030-drops-89978},
  doi =		{10.4230/LIPIcs.ECRTS.2018.6},
  annote =	{Keywords: deadline miss probability, multinomial-based approach, analytical bound}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2018.8
Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems

Authors: Jian-Jia Chen, Georg von der Brüggen, and Niklas Ueter

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

Abstract
The sporadic task model is often used to analyze recurrent execution of tasks in real-time systems. A sporadic task defines an infinite sequence of task instances, also called jobs, that arrive under the minimum inter-arrival time constraint. To ensure the system safety, timeliness has to be guaranteed in addition to functional correctness, i.e., all jobs of all tasks have to be finished before the job deadlines. We focus on analyzing arbitrary-deadline task sets on a homogeneous (identical) multiprocessor system under any given global fixed-priority scheduling approach and provide a series of schedulability tests with different tradeoffs between their time complexity and their accuracy. Under the arbitrary-deadline setting, the relative deadline of a task can be longer than the minimum inter-arrival time of the jobs of the task. We show that global deadline-monotonic (DM) scheduling has a speedup bound of 3-1/M against any optimal scheduling algorithms, where M is the number of identical processors, and prove that this bound is asymptotically tight.
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Jian-Jia Chen, Georg von der Brüggen, and Niklas Ueter. Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 8:1-8:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{chen_et_al:LIPIcs.ECRTS.2018.8,
  author =	{Chen, Jian-Jia and von der Br\"{u}ggen, Georg and Ueter, Niklas},
  title =	{{Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{8:1--8:24},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2018.8},
  URN =		{urn:nbn:de:0030-drops-89965},
  doi =		{10.4230/LIPIcs.ECRTS.2018.8},
  annote =	{Keywords: global fixed-priority scheduling, schedulability analyses, speedup bounds}
}
Document
DOI: 10.4230/DARTS.4.2.6
Evaluations of Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems (Artifact)

Authors: Jian-Jia Chen, Georg von der Brüggen, and Niklas Ueter

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

Abstract
This artifact provides the experimental details and implementations of all the facilitated schedulability tests used in the reported acceptance ratio based evaluations as documented in the related paper "Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems".
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Jian-Jia Chen, Georg von der Brüggen, and Niklas Ueter. Evaluations of Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems (Artifact). In Special Issue of the 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Dagstuhl Artifacts Series (DARTS), Volume 4, Issue 2, pp. 6:1-6:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{chen_et_al:DARTS.4.2.6,
  author =	{Chen, Jian-Jia and von der Br\"{u}ggen, Georg and Ueter, Niklas},
  title =	{{Evaluations of Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems (Artifact)}},
  pages =	{6:1--6:5},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2018},
  volume =	{4},
  number =	{2},
  editor =	{Chen, Jian-Jia and von der Br\"{u}ggen, Georg and Ueter, Niklas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DARTS.4.2.6},
  URN =		{urn:nbn:de:0030-drops-89746},
  doi =		{10.4230/DARTS.4.2.6},
  annote =	{Keywords: global fixed-priority scheduling, schedulability analyses, speedup bounds}
}
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-dev.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.2017.9
On the Pitfalls of Resource Augmentation Factors and Utilization Bounds in Real-Time Scheduling

Authors: Jian-Jia Chen, Georg von der Brüggen, Wen-Hung Huang, and Robert I. Davis

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

Abstract
In this paper, we take a careful look at speedup factors, utilization bounds, and capacity augmentation bounds. These three metrics have been widely adopted in real-time scheduling research as the de facto standard theoretical tools for assessing scheduling algorithms and schedulability tests. Despite that, it is not always clear how researchers and designers should interpret or use these metrics. In studying this area, we found a number of surprising results, and related to them, ways in which the metrics may be misinterpreted or misunderstood. In this paper, we provide a perspective on the use of these metrics, guiding researchers on their meaning and interpretation, and helping to avoid pitfalls in their use. Finally, we propose and demonstrate the use of parametric augmentation functions as a means of providing nuanced information that may be more relevant in practical settings.
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Jian-Jia Chen, Georg von der Brüggen, Wen-Hung Huang, and Robert I. Davis. On the Pitfalls of Resource Augmentation Factors and Utilization Bounds in Real-Time Scheduling. In 29th Euromicro Conference on Real-Time Systems (ECRTS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 76, pp. 9:1-9:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{chen_et_al:LIPIcs.ECRTS.2017.9,
  author =	{Chen, Jian-Jia and von der Br\"{u}ggen, Georg and Huang, Wen-Hung and Davis, Robert I.},
  title =	{{On the Pitfalls of Resource Augmentation Factors and Utilization Bounds in Real-Time Scheduling}},
  booktitle =	{29th Euromicro Conference on Real-Time Systems (ECRTS 2017)},
  pages =	{9:1--9:25},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2017.9},
  URN =		{urn:nbn:de:0030-drops-71619},
  doi =		{10.4230/LIPIcs.ECRTS.2017.9},
  annote =	{Keywords: Real-time systems, speedup factors, utilization bounds, capacity augmentation bounds}
}
Document
DOI: 10.4230/LITES-v004-i001-a001
A Note on the Period Enforcer Algorithm for Self-Suspending Tasks

Authors: Jian-Jia Chen and Björn B. Brandenburg

Published in: LITES, Volume 4, Issue 1 (2017). Leibniz Transactions on Embedded Systems, Volume 4, Issue 1

Abstract
The period enforcer algorithm for self-suspending real-time tasks is a technique for suppressing the "back-to-back" scheduling penalty associated with deferred execution. Originally proposed in 1991, the algorithm has attracted renewed interest in recent years. This note revisits the algorithm in the light of recent developments in the analysis of self-suspending tasks, carefully re-examines and explains its underlying assumptions and limitations, and points out three observations that have not been made in the literature to date: (i) period enforcement is not strictly superior (compared to the base case without enforcement) as it can cause deadline misses in self-suspending task sets that are schedulable without enforcement; (ii) to match the assumptions underlying the analysis of the period enforcer, a schedulability analysis of self-suspending tasks subject to period enforcement requires a task set  transformation for which no solution is known  in the general case, and which is subject to exponential time complexity (with current techniques) in the limited case of a single self-suspending task; and (iii) the period enforcer algorithm is incompatible with all existing analyses of suspension-based locking protocols, and can in fact cause ever-increasing suspension times until a deadline is missed.
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Jian-Jia Chen and Björn B. Brandenburg. A Note on the Period Enforcer Algorithm for Self-Suspending Tasks. In LITES, Volume 4, Issue 1 (2017). Leibniz Transactions on Embedded Systems, Volume 4, Issue 1, pp. 01:1-01:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@Article{chen_et_al:LITES-v004-i001-a001,
  author =	{Chen, Jian-Jia and Brandenburg, Bj\"{o}rn B.},
  title =	{{A Note on the Period Enforcer Algorithm for Self-Suspending Tasks}},
  journal =	{Leibniz Transactions on Embedded Systems},
  pages =	{01:1--01:22},
  ISSN =	{2199-2002},
  year =	{2017},
  volume =	{4},
  number =	{1},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LITES-v004-i001-a001},
  doi =		{10.4230/LITES-v004-i001-a001},
  annote =	{Keywords: Period Enforcer, Deferred Execution, Self-suspension, Blocking}
}
Document
DOI: 10.4230/LITES-v001-i002-a002
Computation Offloading for Frame-Based Real-Time Tasks under Given Server Response Time Guarantees

Authors: Anas S. M. Toma and Jian-Jia Chen

Published in: LITES, Volume 1, Issue 2 (2014). Leibniz Transactions on Embedded Systems, Volume 1, Issue 2

Abstract
Computation offloading has been adopted to improve the performance of embedded systems by offloading the computation of some tasks, especially computation-intensive tasks, to servers or clouds. This paper explores computation offloading for real-time tasks in embedded systems, provided given response time guarantees from the servers, to decide which tasks should be offloaded to get the results in time. We consider frame-based real-time tasks with the same period and relative deadline. When the execution order of the tasks is given, the problem can be solved in linear time. However, when the execution order is not specified, we prove that the problem is NP-complete. We develop a pseudo-polynomial-time algorithm for deriving feasible schedules, if they exist.  An approximation scheme is also developed to trade the error made from the algorithm and the complexity. Our algorithms are extended to minimize the period/relative deadline of the tasks for performance maximization. The algorithms are evaluated with a case study for a surveillance system and synthesized benchmarks.
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Anas S. M. Toma and Jian-Jia Chen. Computation Offloading for Frame-Based Real-Time Tasks under Given Server Response Time Guarantees. In LITES, Volume 1, Issue 2 (2014). Leibniz Transactions on Embedded Systems, Volume 1, Issue 2, pp. 02:1-02:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@Article{toma_et_al:LITES-v001-i002-a002,
  author =	{Toma, Anas S. M. and Chen, Jian-Jia},
  title =	{{Computation Offloading for Frame-Based Real-Time Tasks under Given Server Response Time Guarantees}},
  journal =	{Leibniz Transactions on Embedded Systems},
  pages =	{02:1--02:21},
  ISSN =	{2199-2002},
  year =	{2014},
  volume =	{1},
  number =	{2},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LITES-v001-i002-a002},
  doi =		{10.4230/LITES-v001-i002-a002},
  annote =	{Keywords: Computation offloading, Task scheduling, Real-time systems}
}
Document
DOI: 10.4230/LIPIcs.STACS.2014.226
Online Dynamic Power Management with Hard Real-Time Guarantees

Authors: Jian-Jia Chen, Mong-Jen Kao, D.T. Lee, Ignaz Rutter, and Dorothea Wagner

Published in: LIPIcs, Volume 25, 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)

Abstract
We consider the problem of online dynamic power management that provides hard real-time guarantees for multi-processor systems. In this problem, a set of jobs, each associated with an arrival time, a deadline, and an execution time, arrives to the system in an online fashion. The objective is to compute a non-migrative preemptive schedule of the jobs and a sequence of power on/off operations of the processors so as to minimize the total energy consumption while ensuring that all the deadlines of the jobs are met. We assume that we can use as many processors as necessary. In this paper we examine the complexity of this problem and provide online strategies that lead to practical energy-efficient solutions for real-time multi-processor systems. First, we consider the case for which we know in advance that the set of jobs can be scheduled feasibly on a single processor. We show that, even in this case, the competitive factor of any online algorithm is at least 2.06. On the other hand, we give a 4-competitive online algorithm that uses at most two processors. For jobs with unit execution times, the competitive factor of this algorithm improves to 3.59. Second, we relax our assumption by considering as input multiple streams of jobs, each of which can be scheduled feasibly on a single processor. We present a trade-off between the energy-efficiency of the schedule and the number of processors to be used. More specifically, for k given job streams and h processors with h>k, we give a scheduling strategy such that the energy usage is at most 4.k/(h-k) times that used by any schedule which schedules each of the k streams on a separate processor. Finally, we drop the assumptions on the input set of jobs. We show that the competitive factor of any online algorithm is at least 2.28, even for the case of unit job execution times for which we further derive an O(1)-competitive algorithm.
Cite as

Jian-Jia Chen, Mong-Jen Kao, D.T. Lee, Ignaz Rutter, and Dorothea Wagner. Online Dynamic Power Management with Hard Real-Time Guarantees. In 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014). Leibniz International Proceedings in Informatics (LIPIcs), Volume 25, pp. 226-238, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{chen_et_al:LIPIcs.STACS.2014.226,
  author =	{Chen, Jian-Jia and Kao, Mong-Jen and Lee, D.T. and Rutter, Ignaz and Wagner, Dorothea},
  title =	{{Online Dynamic Power Management with Hard Real-Time Guarantees}},
  booktitle =	{31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)},
  pages =	{226--238},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-65-1},
  ISSN =	{1868-8969},
  year =	{2014},
  volume =	{25},
  editor =	{Mayr, Ernst W. and Portier, Natacha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2014.226},
  URN =		{urn:nbn:de:0030-drops-44607},
  doi =		{10.4230/LIPIcs.STACS.2014.226},
  annote =	{Keywords: Energy-Efficient Scheduling, Online Dynamic Power Management}
}
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