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Documents authored by Freitag, Johannes


Document
Virtual Timing Isolation for Mixed-Criticality Systems

Authors: Johannes Freitag, Sascha Uhrig, and Theo Ungerer

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


Abstract
Commercial of the shelf multicore processors suffer from timing interferences between cores which complicates applying them in hard real-time systems like avionic applications. This paper proposes a virtual timing isolation of one main application running on one core from all other cores. The proposed technique is based on hardware external to the multicore processor and completely transparent to the main application i.e., no modifications of the software including the operating system are necessary. The basic idea is to apply a single-core execution based Worst Case Execution Time analysis and to accept a predefined slowdown during multicore execution. If the slowdown exceeds the acceptable bounds, interferences will be reduced by controlling the behavior of low-critical cores to keep the main application's progress inside the given bounds. Apart from the main goal of isolating the timing of the critical application a subgoal is also to efficiently use the other cores. For that purpose, three different mechanisms for controlling the non-critical cores are compared regarding efficient usage of the complete processor. Measuring the progress of the main application is performed by tracking the application's Fingerprint. This technology quantifies online any slowdown of execution compared to a given baseline (single-core execution). Several countermeasures to compensate unacceptable slowdowns are proposed and evaluated in this paper, together with an accuracy evaluation of the Fingerprinting. Our evaluations using the TACLeBench benchmark suite show that we can meet a given acceptable timing bound of 4 percent slowdown with a resulting real slowdown of only 3.27 percent in case of a pulse width modulated control and of 4.44 percent in the case of a frequency scaling control.

Cite as

Johannes Freitag, Sascha Uhrig, and Theo Ungerer. Virtual Timing Isolation for Mixed-Criticality Systems. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 13:1-13:23, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2018)


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@InProceedings{freitag_et_al:LIPIcs.ECRTS.2018.13,
  author =	{Freitag, Johannes and Uhrig, Sascha and Ungerer, Theo},
  title =	{{Virtual Timing Isolation for Mixed-Criticality Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{13:1--13:23},
  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.2018.13},
  URN =		{urn:nbn:de:0030-drops-89904},
  doi =		{10.4230/LIPIcs.ECRTS.2018.13},
  annote =	{Keywords: multicore, hard real-time systems, timing isolation, safety-critical systems, mixed-criticality design and assurance}
}
Document
Contention-Aware Dynamic Memory Bandwidth Isolation with Predictability in COTS Multicores: An Avionics Case Study

Authors: Ankit Agrawal, Gerhard Fohler, Johannes Freitag, Jan Nowotsch, Sascha Uhrig, and Michael Paulitsch

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


Abstract
Airbus is investigating COTS multicore platforms for safety-critical avionics applications, pursuing helicopter-style autonomous and electric aircraft. These aircraft need to be ultra-lightweight for future mobility in the urban city landscape. As a step towards certification, Airbus identified the need for new methods that preserve the ARINC 653 single core schedule of a Helicopter Terrain Awareness and Warning System (HTAWS) application while scheduling additional safety-critical partitions on the other cores. As some partitions in the HTAWS application are memory-intensive, static memory bandwidth throttling may lead to slow down of such partitions or provide only little remaining bandwidth to the other cores. Thus, there is a need for dynamic memory bandwidth isolation. This poses new challenges for scheduling, as execution times and scheduling become interdependent: scheduling requires execution times as input, which depends on memory latencies and contention from memory accesses of other cores - which are determined by scheduling. Furthermore, execution times depend on memory access patterns. In this paper, we propose a method to solve this problem for slot-based time-triggered systems without requiring application source-code modifications using a number of dynamic memory bandwidth levels. It is NoC and DRAM controller contention-aware and based on the existing interference-sensitive WCET computation and the memory bandwidth throttling mechanism. It constructs schedule tables by assigning partitions and dynamic memory bandwidth to each slot on each core, considering worst case memory access patterns. Then at runtime, two servers - for processing time and memory bandwidth - run on each core, jointly controlling the contention between the cores and the amount of memory accesses per slot. As a proof-of-concept, we use a constraint solver to construct tables. Experiments on the P4080 COTS multicore platform, using a research OS from Airbus and EEMBC benchmarks, demonstrate that our proposed method enables preserving existing schedules on a core while scheduling additional safety-critical partitions on other cores, and meets dynamic memory bandwidth isolation requirements.

Cite as

Ankit Agrawal, Gerhard Fohler, Johannes Freitag, Jan Nowotsch, Sascha Uhrig, and Michael Paulitsch. Contention-Aware Dynamic Memory Bandwidth Isolation with Predictability in COTS Multicores: An Avionics Case Study. In 29th Euromicro Conference on Real-Time Systems (ECRTS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 76, pp. 2:1-2:22, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2017)


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@InProceedings{agrawal_et_al:LIPIcs.ECRTS.2017.2,
  author =	{Agrawal, Ankit and Fohler, Gerhard and Freitag, Johannes and Nowotsch, Jan and Uhrig, Sascha and Paulitsch, Michael},
  title =	{{Contention-Aware Dynamic Memory Bandwidth Isolation with Predictability in COTS Multicores: An Avionics Case Study}},
  booktitle =	{29th Euromicro Conference on Real-Time Systems (ECRTS 2017)},
  pages =	{2:1--2:22},
  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.2017.2},
  URN =		{urn:nbn:de:0030-drops-71740},
  doi =		{10.4230/LIPIcs.ECRTS.2017.2},
  annote =	{Keywords: Dynamic memory bandwidth isolation, Safety-critical avionics, COTS multicores}
}
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