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Documents authored by Nasri, Mitra


Document
Response-Time Analysis for Non-Preemptive Periodic Moldable Gang Tasks

Authors: Geoffrey Nelissen, Joan Marcè i Igual, and Mitra Nasri

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


Abstract
Gang scheduling has long been adopted by the high-performance computing community as a way to reduce the synchronization overhead between related threads. It allows for several threads to execute in lock steps without suffering from long busy-wait periods or be penalized by large context-switch overheads. When combined with non-preemptive execution, gang scheduling significantly reduces the execution time of threads that work on the same data by decreasing the number of memory transactions required to load or store the data. In this work, we focus on two main types of gang tasks: rigid and moldable. A moldable gang task has a presumed known minimum and maximum number of cores on which it can be executed at runtime, while a rigid gang task always executes on the same number of cores. This work presents the first response-time analysis for non-preemptive moldable gang tasks. Our analysis is based on the notion of schedule abstraction; a new approach for response-time analysis with the promise of high accuracy. Our experiments on periodic rigid gang tasks show that our analysis is 4.9 times more successful in identifying schedulable tasks than the existing utilization-based test for rigid gang tasks.

Cite as

Geoffrey Nelissen, Joan Marcè i Igual, and Mitra Nasri. Response-Time Analysis for Non-Preemptive Periodic Moldable Gang Tasks. In 34th Euromicro Conference on Real-Time Systems (ECRTS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 231, pp. 12:1-12:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{nelissen_et_al:LIPIcs.ECRTS.2022.12,
  author =	{Nelissen, Geoffrey and Marc\`{e} i Igual, Joan and Nasri, Mitra},
  title =	{{Response-Time Analysis for Non-Preemptive Periodic Moldable Gang Tasks}},
  booktitle =	{34th Euromicro Conference on Real-Time Systems (ECRTS 2022)},
  pages =	{12:1--12:22},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2022.12},
  URN =		{urn:nbn:de:0030-drops-163293},
  doi =		{10.4230/LIPIcs.ECRTS.2022.12},
  annote =	{Keywords: schedulability analysis, response time analysis, moldable gang tasks, rigid gang tasks, schedule abstraction graph, multiprocessor, non-preemptive}
}
Document
From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems

Authors: Arpan Gujarati, Mitra Nasri, Rupak Majumdar, and Björn B. Brandenburg

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


Abstract
Estimating metrics such as the Mean Time To Failure (MTTF) or its inverse, the Failures-In-Time (FIT), is a central problem in reliability estimation of safety-critical systems. To this end, prior work in the real-time and embedded systems community has focused on bounding the probability of failures in a single iteration of the control loop, resulting in, for example, the worst-case probability of a message transmission error due to electromagnetic interference, or an upper bound on the probability of a skipped or an incorrect actuation. However, periodic systems, which can be found at the core of most safety-critical real-time systems, are routinely designed to be robust to a single fault or to occasional failures (case in point, control applications are usually robust to a few skipped or misbehaving control loop iterations). Thus, obtaining long-run reliability metrics like MTTF and FIT from single iteration estimates by calculating the time to first fault can be quite pessimistic. Instead, overall system failures for such systems are better characterized using multi-state models such as weakly-hard constraints. In this paper, we describe and empirically evaluate three orthogonal approaches, PMC, Mart, and SAp, for the sound estimation of system’s MTTF, starting from a periodic stochastic model characterizing the failure in a single iteration of a periodic system, and using weakly-hard constraints as a measure of system robustness. PMC and Mart are exact analyses based on Markov chain analysis and martingale theory, respectively, whereas SAp is a sound approximation based on numerical analysis. We evaluate these techniques empirically in terms of their accuracy and numerical precision, their expressiveness for different definitions of weakly-hard constraints, and their space and time complexities, which affect their scalability and applicability in different regions of the space of weakly-hard constraints.

Cite as

Arpan Gujarati, Mitra Nasri, Rupak Majumdar, and Björn B. Brandenburg. From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems. In 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 133, pp. 9:1-9:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{gujarati_et_al:LIPIcs.ECRTS.2019.9,
  author =	{Gujarati, Arpan and Nasri, Mitra and Majumdar, Rupak and Brandenburg, Bj\"{o}rn B.},
  title =	{{From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems}},
  booktitle =	{31st Euromicro Conference on Real-Time Systems (ECRTS 2019)},
  pages =	{9:1--9:23},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2019.9},
  URN =		{urn:nbn:de:0030-drops-107468},
  doi =		{10.4230/LIPIcs.ECRTS.2019.9},
  annote =	{Keywords: reliability analysis, MTTF/FIT analysis, weakly-hard constraints}
}
Document
Response-Time Analysis of Limited-Preemptive Parallel DAG Tasks Under Global Scheduling

Authors: Mitra Nasri, Geoffrey Nelissen, and Björn B. Brandenburg

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


Abstract
Most recurrent real-time applications can be modeled as a set of sequential code segments (or blocks) that must be (repeatedly) executed in a specific order. This paper provides a schedulability analysis for such systems modeled as a set of parallel DAG tasks executed under any limited-preemptive global job-level fixed priority scheduling policy. More precisely, we derive response-time bounds for a set of jobs subject to precedence constraints, release jitter, and execution-time uncertainty, which enables support for a wide variety of parallel, limited-preemptive execution models (e.g., periodic DAG tasks, transactional tasks, generalized multi-frame tasks, etc.). Our analysis explores the space of all possible schedules using a powerful new state abstraction and state-pruning technique. An empirical evaluation shows the analysis to identify between 10 to 90 percentage points more schedulable task sets than the state-of-the-art schedulability test for limited-preemptive sporadic DAG tasks. It scales to systems of up to 64 cores with 20 DAG tasks. Moreover, while our analysis is almost as accurate as the state-of-the-art exact schedulability test based on model checking (for sequential non-preemptive tasks), it is three orders of magnitude faster and hence capable of analyzing task sets with more than 60 tasks on 8 cores in a few seconds.

Cite as

Mitra Nasri, Geoffrey Nelissen, and Björn B. Brandenburg. Response-Time Analysis of Limited-Preemptive Parallel DAG Tasks Under Global Scheduling. In 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 133, pp. 21:1-21:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{nasri_et_al:LIPIcs.ECRTS.2019.21,
  author =	{Nasri, Mitra and Nelissen, Geoffrey and Brandenburg, Bj\"{o}rn B.},
  title =	{{Response-Time Analysis of Limited-Preemptive Parallel DAG Tasks Under Global Scheduling}},
  booktitle =	{31st Euromicro Conference on Real-Time Systems (ECRTS 2019)},
  pages =	{21:1--21:23},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2019.21},
  URN =		{urn:nbn:de:0030-drops-107587},
  doi =		{10.4230/LIPIcs.ECRTS.2019.21},
  annote =	{Keywords: parallel DAG tasks, global multiprocessor scheduling, schedulability analysis, non-preemptive jobs, precedence constraints, worst-case response time, OpenMP}
}
Document
A Response-Time Analysis for Non-Preemptive Job Sets under Global Scheduling

Authors: Mitra Nasri, Geoffrey Nelissen, and Björn B. Brandenburg

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


Abstract
An effective way to increase the timing predictability of multicore platforms is to use non-preemptive scheduling. It reduces preemption and job migration overheads, avoids intra-core cache interference, and improves the accuracy of worst-case execution time (WCET) estimates. However, existing schedulability tests for global non-preemptive multiprocessor scheduling are pessimistic, especially when applied to periodic workloads. This paper reduces this pessimism by introducing a new type of sufficient schedulability analysis that is based on an exploration of the space of possible schedules using concise abstractions and state-pruning techniques. Specifically, we analyze the schedulability of non-preemptive job sets (with bounded release jitter and execution time variation) scheduled by a global job-level fixed-priority (JLFP) scheduling algorithm upon an identical multicore platform. The analysis yields a lower bound on the best-case response-time (BCRT) and an upper bound on the worst-case response time (WCRT) of the jobs. In an empirical evaluation with randomly generated workloads, we show that the method scales to 30 tasks, a hundred thousand jobs (per hyperperiod), and up to 9 cores.

Cite as

Mitra Nasri, Geoffrey Nelissen, and Björn B. Brandenburg. A Response-Time Analysis for Non-Preemptive Job Sets under Global Scheduling. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 9:1-9:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


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@InProceedings{nasri_et_al:LIPIcs.ECRTS.2018.9,
  author =	{Nasri, Mitra and Nelissen, Geoffrey and Brandenburg, Bj\"{o}rn B.},
  title =	{{A Response-Time Analysis for Non-Preemptive Job Sets under Global Scheduling}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{9:1--9:23},
  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.2018.9},
  URN =		{urn:nbn:de:0030-drops-89941},
  doi =		{10.4230/LIPIcs.ECRTS.2018.9},
  annote =	{Keywords: global multiprocessor scheduling, schedulability analysis, non-preemptive tasks, worst-case response time, best-case response time}
}
Document
Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems

Authors: Arpan Gujarati, Mitra Nasri, and Björn B. Brandenburg

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


Abstract
In time-sensitive, safety-critical systems that must be fail-operational, active replication is commonly used to mitigate transient faults that arise due to electromagnetic interference (EMI). However, designing an effective and well-performing active replication scheme is challenging since replication conflicts with the size, weight, power, and cost constraints of embedded applications. To enable a systematic and rigorous exploration of the resulting tradeoffs, we present an analysis to quantify the resiliency of fail-operational networked control systems against EMI-induced memory corruption, host crashes, and retransmission delays. Since control systems are typically robust to a few failed iterations, e.g., one missed actuation does not crash an inverted pendulum, traditional solutions based on hard real-time assumptions are often too pessimistic. Our analysis reduces this pessimism by modeling a control system's inherent robustness as an (m,k)-firm specification. A case study with an active suspension workload indicates that the analytical bounds closely predict the failure rate estimates obtained through simulation, thereby enabling a meaningful design-space exploration, and also demonstrates the utility of the analysis in identifying non-trivial and non-obvious reliability tradeoffs.

Cite as

Arpan Gujarati, Mitra Nasri, and Björn B. Brandenburg. Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 16:1-16:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


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@InProceedings{gujarati_et_al:LIPIcs.ECRTS.2018.16,
  author =	{Gujarati, Arpan and Nasri, Mitra and Brandenburg, Bj\"{o}rn B.},
  title =	{{Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{16:1--16:24},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2018.16},
  URN =		{urn:nbn:de:0030-drops-89884},
  doi =		{10.4230/LIPIcs.ECRTS.2018.16},
  annote =	{Keywords: probabilistic analysis, reliability analysis, networked control systems}
}
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