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DOI: 10.4230/OASIcs.WCET.2015.11

Software-enforced Interconnect Arbitration for COTS Multicores

Authors: Marco Ziccardi, Alessandro Cornaglia, Enrico Mezzetti, and Tullio Vardanega

Published in: OASIcs, Volume 47, 15th International Workshop on Worst-Case Execution Time Analysis (WCET 2015)

Abstract

The advent of multicore processors complicates timing analysis owing to the need to account for the interference between cores accessing shared resources, which is not always easy to characterize in a safe and tight way. Solutions have been proposed that take two distinct but complementary directions: on the one hand, complex analysis techniques have been developed to provide safe and tight bounds to contention; on the other hand, sophisticated arbitration policies (hardware or software) have been proposed to limit or control inter-core interference. In this paper we propose a software-based TDMA-like arbitration of accesses to a shared interconnect (e.g. a bus) that prevents inter-core interference. A more flexible arbitration scheme is also proposed to reserve more bandwidth to selected cores while still avoiding contention. A proof-of-concept implementation on an AURIX TC277TU processor shows that our approach can apply to COTS processors, thus not relying on dedicated hardware arbiters, while introducing little overhead.

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Marco Ziccardi, Alessandro Cornaglia, Enrico Mezzetti, and Tullio Vardanega. Software-enforced Interconnect Arbitration for COTS Multicores. In 15th International Workshop on Worst-Case Execution Time Analysis (WCET 2015). Open Access Series in Informatics (OASIcs), Volume 47, pp. 11-20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{ziccardi_et_al:OASIcs.WCET.2015.11,
  author =	{Ziccardi, Marco and Cornaglia, Alessandro and Mezzetti, Enrico and Vardanega, Tullio},
  title =	{{Software-enforced Interconnect Arbitration for COTS Multicores}},
  booktitle =	{15th International Workshop on Worst-Case Execution Time Analysis (WCET 2015)},
  pages =	{11--20},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-95-8},
  ISSN =	{2190-6807},
  year =	{2015},
  volume =	{47},
  editor =	{Cazorla, Francisco J.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2015.11},
  URN =		{urn:nbn:de:0030-drops-52526},
  doi =		{10.4230/OASIcs.WCET.2015.11},
  annote =	{Keywords: Multicore, Resource Arbitration, Interference, Mixed-Criticality}
}

Document

DOI: 10.4230/LITES-v002-i001-a001

Randomized Caches Can Be Pretty Useful to Hard Real-Time Systems

Authors: Enrico Mezzetti, Marco Ziccardi, Tullio Vardanega, Jaume Abella, Eduardo Quiñones, and Francisco J. Cazorla

Published in: LITES, Volume 2, Issue 1 (2015). Leibniz Transactions on Embedded Systems, Volume 2, Issue 1

Abstract

Cache randomization per se, and its viability for probabilistic timing analysis (PTA) of critical real-time systems, are receiving increasingly close attention from the scientific community and the industrial practitioners. In fact, the very notion of introducing randomness and probabilities in time-critical systems has caused strenuous debates owing to the apparent clash that this idea has with the strictly deterministic view traditionally held for those systems. A paper recently appeared in LITES (Reineke, J. (2014). Randomized Caches Considered Harmful in Hard Real-Time Systems. LITES, 1(1), 03:1-03:13.) provides a critical analysis of the weaknesses and risks entailed in using randomized caches in hard real-time systems. In order to provide the interested reader with a fuller, balanced appreciation of the subject matter, a critical analysis of the benefits brought about by that innovation should be provided also. This short paper addresses that need by revisiting the array of issues addressed in the cited work, in the light of the latest advances to the relevant state of the art. Accordingly, we show that the potential benefits of randomized caches do offset their limitations, causing them to be - when used in conjunction with PTA - a serious competitor to conventional designs.

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Enrico Mezzetti, Marco Ziccardi, Tullio Vardanega, Jaume Abella, Eduardo Quiñones, and Francisco J. Cazorla. Randomized Caches Can Be Pretty Useful to Hard Real-Time Systems. In LITES, Volume 2, Issue 1 (2015). Leibniz Transactions on Embedded Systems, Volume 2, Issue 1, pp. 01:1-01:10, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@Article{mezzetti_et_al:LITES-v002-i001-a001,
  author =	{Mezzetti, Enrico and Ziccardi, Marco and Vardanega, Tullio and Abella, Jaume and Qui\~{n}ones, Eduardo and Cazorla, Francisco J.},
  title =	{{Randomized Caches Can Be Pretty Useful to Hard Real-Time Systems}},
  journal =	{Leibniz Transactions on Embedded Systems},
  pages =	{01:1--01:10},
  ISSN =	{2199-2002},
  year =	{2015},
  volume =	{2},
  number =	{1},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LITES-v002-i001-a001},
  URN =		{urn:nbn:de:0030-drops-192512},
  doi =		{10.4230/LITES-v002-i001-a001},
  annote =	{Keywords: Real-time systems, Probabilistic WCET, Randomized caches}
}

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Software-enforced Interconnect Arbitration for COTS Multicores

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Randomized Caches Can Be Pretty Useful to Hard Real-Time Systems

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