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DOI: 10.4230/LIPIcs.ECRTS.2018.23

Recovery Time Considerations in Real-Time Systems Employing Software Fault Tolerance

Authors: Anand Bhat, Soheil Samii, and Ragunathan (Raj) Rajkumar

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

Abstract

Safety-critical real-time systems like modern automobiles with advanced driving-assist features must employ redundancy for crucial software tasks to tolerate permanent crash faults. This redundancy can be achieved by using techniques like active replication or the primary-backup approach. In such systems, the recovery time which is the amount of time it takes for a redundant task to take over execution on the failure of a primary task becomes a very important design parameter. The recovery time for a given task depends on various factors like task allocation, primary and redundant task priorities, system load and the scheduling policy. Each task can also have a different recovery time requirement (RTR). For example, in automobiles with automated driving features, safety-critical tasks like perception and steering control have strict RTRs, whereas such requirements are more relaxed in the case of tasks like heating control and mission planning. In this paper, we analyze the recovery time for software tasks in a real-time system employing Rate-Monotonic Scheduling (RMS). We derive bounds on the recovery times for different redundant task options and propose techniques to determine the redundant-task type for a task to satisfy its RTR. We also address the fault-tolerant task allocation problem, with the additional constraint of satisfying the RTR of each task in the system. Given that the problem of assigning tasks to processors is a well-known NP-hard bin-packing problem we propose computationally-efficient heuristics to find a feasible allocation of tasks and their redundant copies. We also apply the simulated annealing method to the fault-tolerant task allocation problem with RTR constraints and compare against our heuristics.

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Anand Bhat, Soheil Samii, and Ragunathan (Raj) Rajkumar. Recovery Time Considerations in Real-Time Systems Employing Software Fault Tolerance. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 23:1-23:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{bhat_et_al:LIPIcs.ECRTS.2018.23,
  author =	{Bhat, Anand and Samii, Soheil and Rajkumar, Ragunathan (Raj)},
  title =	{{Recovery Time Considerations in Real-Time Systems Employing Software Fault Tolerance}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{23:1--23:22},
  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.2018.23},
  URN =		{urn:nbn:de:0030-drops-89808},
  doi =		{10.4230/LIPIcs.ECRTS.2018.23},
  annote =	{Keywords: fault tolerance, real-time embedded systems, recovery time, real-time schedulability}
}

Document

DOI: 10.4230/LIPIcs.ECRTS.2017.21

Thermal Implications of Energy-Saving Schedulers

Authors: Sandeep M. D'souza and Ragunathan (Raj) Rajkumar

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

Abstract

In many real-time systems, continuous operation can raise processor temperature, potentially leading to system failure, bodily harm to users, or a reduction in the functional lifetime of a system. Static power dominates the total power consumption, and is also directly proportional to the operating temperature. This reduces the effectiveness of frequency scaling and necessitates the use of sleep states. In this work, we explore the relationship between energy savings and system temperature in the context of fixed-priority energy-saving schedulers, which utilize a processor’s deep-sleep state to save energy. We derive insights from a well-known thermal model, and are able to identify proactive design choices which are independent of system constants and can be used to reduce processor temperature. Our observations indicate that, while energy savings are key to lower temperatures, not all energy-efficient solutions yield low temperatures. Based on these insights, we propose the SysSleep and ThermoSleep algorithms, which enable a thermally-effective sleep schedule. We also derive a lower bound on the optimal temperature achievable by energy-saving schedulers. Additionally, we discuss partitioning and task phasing techniques for multi-core processors, which require all cores to synchronously transition into deep sleep, as well as those which support independent deep-sleep transitions. We observe that, while energy optimization is straightforward in some cases, the dependence of temperature on partitioning and task phasing makes temperature minimization non-trivial. Evaluations show that compared to the existing purely energy-efficient design methodology, our proposed techniques yield lower temperatures along with significant energy savings.

Cite as

Sandeep M. D'souza and Ragunathan (Raj) Rajkumar. Thermal Implications of Energy-Saving Schedulers. In 29th Euromicro Conference on Real-Time Systems (ECRTS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 76, pp. 21:1-21:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{dsouza_et_al:LIPIcs.ECRTS.2017.21,
  author =	{D'souza, Sandeep M. and Rajkumar, Ragunathan (Raj)},
  title =	{{Thermal Implications of Energy-Saving Schedulers}},
  booktitle =	{29th Euromicro Conference on Real-Time Systems (ECRTS 2017)},
  pages =	{21:1--21:23},
  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.2017.21},
  URN =		{urn:nbn:de:0030-drops-71661},
  doi =		{10.4230/LIPIcs.ECRTS.2017.21},
  annote =	{Keywords: Thermal Analysis, Real-Time Scheduling}
}

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Documents authored by Rajkumar, Ragunathan (Raj)

Recovery Time Considerations in Real-Time Systems Employing Software Fault Tolerance

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Thermal Implications of Energy-Saving Schedulers

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