2 Search Results for "Carvalho, Catarina"

Document
DOI: 10.4230/LIPIcs.ECRTS.2020.9
Demystifying the Real-Time Linux Scheduling Latency

Authors: Daniel Bristot de Oliveira, Daniel Casini, Rômulo Silva de Oliveira, and Tommaso Cucinotta

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

Abstract
Linux has become a viable operating system for many real-time workloads. However, the black-box approach adopted by cyclictest, the tool used to evaluate the main real-time metric of the kernel, the scheduling latency, along with the absence of a theoretically-sound description of the in-kernel behavior, sheds some doubts about Linux meriting the real-time adjective. Aiming at clarifying the PREEMPT_RT Linux scheduling latency, this paper leverages the Thread Synchronization Model of Linux to derive a set of properties and rules defining the Linux kernel behavior from a scheduling perspective. These rules are then leveraged to derive a sound bound to the scheduling latency, considering all the sources of delays occurring in all possible sequences of synchronization events in the kernel. This paper also presents a tracing method, efficient in time and memory overheads, to observe the kernel events needed to define the variables used in the analysis. This results in an easy-to-use tool for deriving reliable scheduling latency bounds that can be used in practice. Finally, an experimental analysis compares the cyclictest and the proposed tool, showing that the proposed method can find sound bounds faster with acceptable overheads.
Cite as

Daniel Bristot de Oliveira, Daniel Casini, Rômulo Silva de Oliveira, and Tommaso Cucinotta. Demystifying the Real-Time Linux Scheduling Latency. In 32nd Euromicro Conference on Real-Time Systems (ECRTS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 165, pp. 9:1-9:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{deoliveira_et_al:LIPIcs.ECRTS.2020.9,
  author =	{de Oliveira, Daniel Bristot and Casini, Daniel and de Oliveira, R\^{o}mulo Silva and Cucinotta, Tommaso},
  title =	{{Demystifying the Real-Time Linux Scheduling Latency}},
  booktitle =	{32nd Euromicro Conference on Real-Time Systems (ECRTS 2020)},
  pages =	{9:1--9:23},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2020.9},
  URN =		{urn:nbn:de:0030-drops-123721},
  doi =		{10.4230/LIPIcs.ECRTS.2020.9},
  annote =	{Keywords: Real-time operating systems, Linux kernel, PREEMPT\underlineRT, Scheduling latency}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2017.27
The Complexity of Quantified Constraints Using the Algebraic Formulation

Authors: Catarina Carvalho, Barnaby Martin, and Dmitriy Zhuk

Published in: LIPIcs, Volume 83, 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)

Abstract
Let A be an idempotent algebra on a finite domain. We combine results of Chen, Zhuk and Carvalho et al. to argue that if A satisfies the polynomially generated powers property (PGP), then QCSP(Inv(A)) is in NP. We then use the result of Zhuk to prove a converse, that if Inv(A) satisfies the exponentially generated powers property (EGP), then QCSP(Inv(A)) is co-NP-hard. Since Zhuk proved that only PGP and EGP are possible, we derive a full dichotomy for the QCSP, justifying the moral correctness of what we term the Chen Conjecture. We examine in closer detail the situation for domains of size three. Over any finite domain, the only type of PGP that can occur is switchability. Switchability was introduced by Chen as a generalisation of the already-known Collapsibility. For three-element domain algebras A that are Switchable, we prove that for every finite subset Delta of Inv(A), Pol(Delta) is Collapsible. The significance of this is that, for QCSP on finite structures (over three-element domain), all QCSP tractability explained by Switchability is already explained by Collapsibility. Finally, we present a three-element domain complexity classification vignette, using known as well as derived results.
Cite as

Catarina Carvalho, Barnaby Martin, and Dmitriy Zhuk. The Complexity of Quantified Constraints Using the Algebraic Formulation. In 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 83, pp. 27:1-27:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{carvalho_et_al:LIPIcs.MFCS.2017.27,
  author =	{Carvalho, Catarina and Martin, Barnaby and Zhuk, Dmitriy},
  title =	{{The Complexity of Quantified Constraints Using the Algebraic Formulation}},
  booktitle =	{42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)},
  pages =	{27:1--27:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-046-0},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{83},
  editor =	{Larsen, Kim G. and Bodlaender, Hans L. and Raskin, Jean-Francois},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2017.27},
  URN =		{urn:nbn:de:0030-drops-80793},
  doi =		{10.4230/LIPIcs.MFCS.2017.27},
  annote =	{Keywords: Quantified Constraints, Computational Complexity, Universal Algebra, Constraint Satisfaction}
}
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