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Documents authored by Mezzetti, Enrico

Document
DOI: 10.4230/LIPIcs.ECRTS.2023.5
Quasi Isolation QoS Setups to Control MPSoC Contention in Integrated Software Architectures

Authors: Sergio Garcia-Esteban, Alejandro Serrano-Cases, Jaume Abella, Enrico Mezzetti, and Francisco J. Cazorla

Published in: LIPIcs, Volume 262, 35th Euromicro Conference on Real-Time Systems (ECRTS 2023)

Abstract
The use of integrated architectures, such as integrated modular avionics (IMA) in avionics, IMA-SP in space, and AUTOSAR in automotive, running on Multi-Processor System-on-Chip (MPSoC) is on the rise. Timing isolation among the different software partitions or applications thereof in an integrated architecture is key to simplifying software integration and its timing validation by ensuring the performance of each partition has no or very limited impact on others despite they share MPSoC’s hardware resources. In this work, we contend that the increasing hardware support for Quality of Service (QoS) guarantees in modern MPSoCs can be leveraged via specific setups to provide strong, albeit not full, isolation among different software partitions. We introduce the concept of Quasi Isolation QoS (QIQoS) setups and instantiate it in the Xilinx Zynq UltraScale+. To that end, out of the millions of setups offered by the different QoS mechanisms, we identify specific QoS configurations that isolate the traffic of time-critical software partitions executing in the core cluster from that generated by contender partitions in the programmable logic. Our results show that the selected isolation setup results in performance variations of the partitions run in the computing cores that are below 6 percentage points, even under scenarios with extremely high traffic coming from the programmable logic.
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Sergio Garcia-Esteban, Alejandro Serrano-Cases, Jaume Abella, Enrico Mezzetti, and Francisco J. Cazorla. Quasi Isolation QoS Setups to Control MPSoC Contention in Integrated Software Architectures. In 35th Euromicro Conference on Real-Time Systems (ECRTS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 262, pp. 5:1-5:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{garciaesteban_et_al:LIPIcs.ECRTS.2023.5,
  author =	{Garcia-Esteban, Sergio and Serrano-Cases, Alejandro and Abella, Jaume and Mezzetti, Enrico and Cazorla, Francisco J.},
  title =	{{Quasi Isolation QoS Setups to Control MPSoC Contention in Integrated Software Architectures}},
  booktitle =	{35th Euromicro Conference on Real-Time Systems (ECRTS 2023)},
  pages =	{5:1--5:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-280-8},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{262},
  editor =	{Papadopoulos, Alessandro V.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2023.5},
  URN =		{urn:nbn:de:0030-drops-180346},
  doi =		{10.4230/LIPIcs.ECRTS.2023.5},
  annote =	{Keywords: Multicore, Interference, QoS}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2022.4
Using Quantile Regression in Neural Networks for Contention Prediction in Multicore Processors

Authors: Axel Brando, Isabel Serra, Enrico Mezzetti, Jaume Abella, and Francisco J. Cazorla

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

Abstract
The development of multicore-based embedded real-time systems is a complex process that encompasses several phases. During the software design and development phases (DDP), and prior to the validation phase, key decisions are taken that cover several aspects of the system under development, from hardware selection and configuration, to the identification and mapping of software functions to the processing nodes. The timing dimension steers a large fraction of those decisions as the correctness of the final system ultimately depends on the implemented functions being able to execute within the allotted time budgets. Early execution time figures already in the DDP are thus needed to prevent flawed design decisions resulting in timing misbehavior being intercepted at the timing analysis step in the advanced development phases, when rolling back to different design decisions is extremely onerous. Multicore timing interference compounds this situation as it has been shown to largely impact execution time of tasks and, therefore, must be factored in when deriving early timing bounds. To effectively prevent misconfigurations while preserving resource efficiency, early timing estimates, typically derived from previous projects or early versions of the software functions, should conservatively and tightly overestimate the timing requirements of the final system configuration including multicore contention. In this work, we show that multi-linear regression (MLR) models and neural network (NN) models can be used to predict the impact of multicore contention on tasks' execution time and hence, derive contention-aware early time budgets, as soon as a release (binary) of the application is available. However, those techniques widely used in the mainstream domain minimize the average/mean case and the predicted impact of contention frequently underestimates the impact that can potentially arise at run time. In order to cover this gap, we propose the use of quantile regression neural networks (QRNN), which are specifically designed to predict the desired high quantile. QRNN reduces the number of underestimations compared to MLR and NN models while containing the overestimation by preserving the high quality prediction. For a set of workloads composed by representative kernels running on a NXP T2080 processor, QRNN reduces the number of underestimations to 8.8% compared to 46.8% and 31.3% for MLR and NN models respectively, while keeping the average over estimation in 1%. QRNN exposes a parameter, the target quantile, that allows controlling the behavior of the predictions so it adapts to user’s needs.
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Axel Brando, Isabel Serra, Enrico Mezzetti, Jaume Abella, and Francisco J. Cazorla. Using Quantile Regression in Neural Networks for Contention Prediction in Multicore Processors. In 34th Euromicro Conference on Real-Time Systems (ECRTS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 231, pp. 4:1-4:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{brando_et_al:LIPIcs.ECRTS.2022.4,
  author =	{Brando, Axel and Serra, Isabel and Mezzetti, Enrico and Abella, Jaume and Cazorla, Francisco J.},
  title =	{{Using Quantile Regression in Neural Networks for Contention Prediction in Multicore Processors}},
  booktitle =	{34th Euromicro Conference on Real-Time Systems (ECRTS 2022)},
  pages =	{4:1--4:25},
  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.2022.4},
  URN =		{urn:nbn:de:0030-drops-163213},
  doi =		{10.4230/LIPIcs.ECRTS.2022.4},
  annote =	{Keywords: Neural Networks, Quantile Prediction, Multicore Contention}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2022.20
Using Markov’s Inequality with Power-Of-k Function for Probabilistic WCET Estimation

Authors: Sergi Vilardell, Isabel Serra, Enrico Mezzetti, Jaume Abella, Francisco J. Cazorla, and Joan del Castillo

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

Abstract
Deriving WCET estimates for software programs with probabilistic means (a.k.a. pWCET estimation) has received significant attention during last years as a way to deal with the increased complexity of the processors used in real-time systems. Many works build on Extreme Value Theory (EVT) that is fed with a sample of the collected data (execution times). In its application, EVT carries two sources of uncertainty: the first one that is intrinsic to the EVT model and relates to determining the subset of the sample that belongs to the (upper) tail, and hence, is actually used by EVT for prediction; and the second one that is induced by the sampling process and hence is inherent to all sample-based methods. In this work, we show that Markov’s inequality can be used to obtain provable trustworthy probabilistic bounds to the tail of a distribution without incurring any model-intrinsic uncertainty. Yet, it produces pessimistic estimates that we shave substantially by proposing the use of a power-of-k function instead of the default identity function used by Markov’s inequality. Lastly, we propose a method to deal with sampling uncertainty for Markov’s inequality that consistently improves EVT estimates on synthetic and real data obtained from a railway application.
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Sergi Vilardell, Isabel Serra, Enrico Mezzetti, Jaume Abella, Francisco J. Cazorla, and Joan del Castillo. Using Markov’s Inequality with Power-Of-k Function for Probabilistic WCET Estimation. In 34th Euromicro Conference on Real-Time Systems (ECRTS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 231, pp. 20:1-20:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{vilardell_et_al:LIPIcs.ECRTS.2022.20,
  author =	{Vilardell, Sergi and Serra, Isabel and Mezzetti, Enrico and Abella, Jaume and Cazorla, Francisco J. and del Castillo, Joan},
  title =	{{Using Markov’s Inequality with Power-Of-k Function for Probabilistic WCET Estimation}},
  booktitle =	{34th Euromicro Conference on Real-Time Systems (ECRTS 2022)},
  pages =	{20:1--20:24},
  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.2022.20},
  URN =		{urn:nbn:de:0030-drops-163377},
  doi =		{10.4230/LIPIcs.ECRTS.2022.20},
  annote =	{Keywords: Markov’s inequality, probabilistic time estimates, probabilistic WCET, Extreme Value Theory}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2021.3
Leveraging Hardware QoS to Control Contention in the Xilinx Zynq UltraScale+ MPSoC

Authors: Alejandro Serrano-Cases, Juan M. Reina, Jaume Abella, Enrico Mezzetti, and Francisco J. Cazorla

Published in: LIPIcs, Volume 196, 33rd Euromicro Conference on Real-Time Systems (ECRTS 2021)

Abstract
The interference co-running tasks generate on each other’s timing behavior continues to be one of the main challenges to be addressed before Multi-Processor System-on-Chip (MPSoCs) are fully embraced in critical systems like those deployed in avionics and automotive domains. Modern MPSoCs like the Xilinx Zynq UltraScale+ incorporate hardware Quality of Service (QoS) mechanisms that can help controlling contention among tasks. Given the distributed nature of modern MPSoCs, the route a request follows from its source (usually a compute element like a CPU) to its target (usually a memory) crosses several QoS points, each one potentially implementing a different QoS mechanism. Mastering QoS mechanisms individually, as well as their combined operation, is pivotal to obtain the expected benefits from the QoS support. In this work, we perform, to our knowledge, the first qualitative and quantitative analysis of the distributed QoS mechanisms in the Xilinx UltraScale+ MPSoC. We empirically derive QoS information not covered by the technical documentation, and show limitations and benefits of the available QoS support. To that end, we use a case study building on neural network kernels commonly used in autonomous systems in different real-time domains.
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Alejandro Serrano-Cases, Juan M. Reina, Jaume Abella, Enrico Mezzetti, and Francisco J. Cazorla. Leveraging Hardware QoS to Control Contention in the Xilinx Zynq UltraScale+ MPSoC. In 33rd Euromicro Conference on Real-Time Systems (ECRTS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 196, pp. 3:1-3:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{serranocases_et_al:LIPIcs.ECRTS.2021.3,
  author =	{Serrano-Cases, Alejandro and Reina, Juan M. and Abella, Jaume and Mezzetti, Enrico and Cazorla, Francisco J.},
  title =	{{Leveraging Hardware QoS to Control Contention in the Xilinx Zynq UltraScale+ MPSoC}},
  booktitle =	{33rd Euromicro Conference on Real-Time Systems (ECRTS 2021)},
  pages =	{3:1--3:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-192-4},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{196},
  editor =	{Brandenburg, Bj\"{o}rn B.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2021.3},
  URN =		{urn:nbn:de:0030-drops-139340},
  doi =		{10.4230/LIPIcs.ECRTS.2021.3},
  annote =	{Keywords: Quality of Service, Real-Time Systems, MPSoC, Multicore Contention}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2020.15
Tracing Hardware Monitors in the GR712RC Multicore Platform: Challenges and Lessons Learnt from a Space Case Study

Authors: Xavier Palomo, Mikel Fernandez, Sylvain Girbal, Enrico Mezzetti, Jaume Abella, Francisco J. Cazorla, and Laurent Rioux

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

Abstract
The demand for increased computing performance is driving industry in critical-embedded systems (CES) domains, e.g. space, towards the use of multicores processors. Multicores, however, pose several challenges that must be addressed before their safe adoption in critical embedded domains. One of the prominent challenges is software timing analysis, a fundamental step in the verification and validation process. Monitoring and profiling solutions, traditionally used for debugging and optimization, are increasingly exploited for software timing in multicores. In particular, hardware event monitors related to requests to shared hardware resources are building block to assess and restraining multicore interference. Modern timing analysis techniques build on event monitors to track and control the contention tasks can generate each other in a multicore platform. In this paper we look into the hardware profiling problem from an industrial perspective and address both methodological and practical problems when monitoring a multicore application. We assess pros and cons of several profiling and tracing solutions, showing that several aspects need to be taken into account while considering the appropriate mechanism to collect and extract the profiling information from a multicore COTS platform. We address the profiling problem on a representative COTS platform for the aerospace domain to find that the availability of directly-accessible hardware counters is not a given, and it may be necessary to the develop specific tools that capture the needs of both the user’s and the timing analysis technique requirements. We report challenges in developing an event monitor tracing tool that works for bare-metal and RTEMS configurations and show the accuracy of the developed tool-set in profiling a real aerospace application. We also show how the profiling tools can be exploited, together with handcrafted benchmarks, to characterize the application behavior in terms of multicore timing interference.
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Xavier Palomo, Mikel Fernandez, Sylvain Girbal, Enrico Mezzetti, Jaume Abella, Francisco J. Cazorla, and Laurent Rioux. Tracing Hardware Monitors in the GR712RC Multicore Platform: Challenges and Lessons Learnt from a Space Case Study. In 32nd Euromicro Conference on Real-Time Systems (ECRTS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 165, pp. 15:1-15:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{palomo_et_al:LIPIcs.ECRTS.2020.15,
  author =	{Palomo, Xavier and Fernandez, Mikel and Girbal, Sylvain and Mezzetti, Enrico and Abella, Jaume and Cazorla, Francisco J. and Rioux, Laurent},
  title =	{{Tracing Hardware Monitors in the GR712RC Multicore Platform: Challenges and Lessons Learnt from a Space Case Study}},
  booktitle =	{32nd Euromicro Conference on Real-Time Systems (ECRTS 2020)},
  pages =	{15:1--15:25},
  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.2020.15},
  URN =		{urn:nbn:de:0030-drops-123787},
  doi =		{10.4230/LIPIcs.ECRTS.2020.15},
  annote =	{Keywords: Multicore Contention, Timing interference, Hardware Event Counters, PMC}
}
Document
DOI: 10.4230/OASIcs.WCET.2019.3
ePAPI: Performance Application Programming Interface for Embedded Platforms

Authors: Jeremy Giesen, Enrico Mezzetti, Jaume Abella, Enrique Fernández, and Francisco J. Cazorla

Published in: OASIcs, Volume 72, 19th International Workshop on Worst-Case Execution Time Analysis (WCET 2019)

Abstract
Performance Monitoring Counters (PMCs) have been traditionally used in the mainstream computing domain to perform debugging and optimization of software performance. PMCs are increasingly considered in embedded time-critical domains to collect in-depth information, e.g. cache misses and memory accesses, of software execution time on complex multicore platforms. In main-stream platforms, standardized specifications and applications like the Performance Application Programming Interface (PAPI) and perf have been proposed to deal with variable PMC support across platforms, by providing a shared interface for configuring and collecting traceable events. However, no equivalent solution exists for embedded critical processors for which the user is required to deal with low-level, platform-specific, and error-prone manipulation of PMC registers. In this paper, we address the need for a standardized PMC interface in the embedded domain, especially in view to support timing characterization of embedded platforms. We assess the compatibility of the PAPI interface with the PMC support available on the AURIX TC297, a reference automotive platform, and we implement and validate ePAPI, the first functionally-equivalent and low-overhead implementation of PAPI for the considered embedded platform.
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Jeremy Giesen, Enrico Mezzetti, Jaume Abella, Enrique Fernández, and Francisco J. Cazorla. ePAPI: Performance Application Programming Interface for Embedded Platforms. In 19th International Workshop on Worst-Case Execution Time Analysis (WCET 2019). Open Access Series in Informatics (OASIcs), Volume 72, pp. 3:1-3:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{giesen_et_al:OASIcs.WCET.2019.3,
  author =	{Giesen, Jeremy and Mezzetti, Enrico and Abella, Jaume and Fern\'{a}ndez, Enrique and Cazorla, Francisco J.},
  title =	{{ePAPI: Performance Application Programming Interface for Embedded Platforms}},
  booktitle =	{19th International Workshop on Worst-Case Execution Time Analysis (WCET 2019)},
  pages =	{3:1--3:13},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-118-4},
  ISSN =	{2190-6807},
  year =	{2019},
  volume =	{72},
  editor =	{Altmeyer, Sebastian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2019.3},
  URN =		{urn:nbn:de:0030-drops-107682},
  doi =		{10.4230/OASIcs.WCET.2019.3},
  annote =	{Keywords: Monitoring counters, embedded systems}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2019.23
Generating and Exploiting Deep Learning Variants to Increase Heterogeneous Resource Utilization in the NVIDIA Xavier

Authors: Roger Pujol, Hamid Tabani, Leonidas Kosmidis, Enrico Mezzetti, Jaume Abella, and Francisco J. Cazorla

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

Abstract
Deep learning-based solutions and, in particular, deep neural networks (DNNs) are at the heart of several functionalities in critical-real time embedded systems (CRTES) from vision-based perception (object detection and tracking) systems to trajectory planning. As a result, several DNN instances simultaneously run at any time on the same computing platform. However, while modern GPUs offer a variety of computing elements (e.g. CPUs, GPUs, and specific accelerators) in which those DNN tasks can be executed depending on their computational requirements and temporal constraints, current DNNs are mainly programmed to exploit one of them, namely, regular cores in the GPU. This creates resource imbalance and under-utilization of GPU resources when executing several DNN instances, causing an increase in DNN tasks' execution time requirements. In this paper, (a) we develop different variants (implementations) of well-known DNN libraries used in the Apollo Autonomous Driving (AD) software for each of the computing elements of the latest NVIDIA Xavier SoC. Each variant can be configured to balance resource requirements and performance: the regular CPU core implementation that can run on 2, 4, and 6 cores; the GPU regular and Tensor core variants that can run in 4 or 8 GPU’s Streaming Multiprocessors (SM); and 1 or 2 NVIDIA’s Deep Learning Accelerators (NVDLA); (b) we show that each particular variant/configuration offers a different resource utilization/performance point; finally, (c) we show how those heterogeneous computing elements can be exploited by a static scheduler to sustain the execution of multiple and diverse DNN variants on the same platform.
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Roger Pujol, Hamid Tabani, Leonidas Kosmidis, Enrico Mezzetti, Jaume Abella, and Francisco J. Cazorla. Generating and Exploiting Deep Learning Variants to Increase Heterogeneous Resource Utilization in the NVIDIA Xavier. In 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 133, pp. 23:1-23:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{pujol_et_al:LIPIcs.ECRTS.2019.23,
  author =	{Pujol, Roger and Tabani, Hamid and Kosmidis, Leonidas and Mezzetti, Enrico and Abella, Jaume and Cazorla, Francisco J.},
  title =	{{Generating and Exploiting Deep Learning Variants to Increase Heterogeneous Resource Utilization in the NVIDIA Xavier}},
  booktitle =	{31st Euromicro Conference on Real-Time Systems (ECRTS 2019)},
  pages =	{23:1--23:23},
  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.2019.23},
  URN =		{urn:nbn:de:0030-drops-107608},
  doi =		{10.4230/LIPIcs.ECRTS.2019.23},
  annote =	{Keywords: Deep Neural Network (DNN), GPU, Heterogenous Resources}
}
Document
DOI: 10.4230/OASIcs.WCET.2016.1
Mitigating Software-Instrumentation Cache Effects in Measurement-Based Timing Analysis

Authors: Enrique Díaz, Jaume Abella, Enrico Mezzetti, Irune Agirre, Mikel Azkarate-Askasua, Tullio Vardanega, and Francisco J. Cazorla

Published in: OASIcs, Volume 55, 16th International Workshop on Worst-Case Execution Time Analysis (WCET 2016)

Abstract
Measurement-based timing analysis (MBTA) is often used to determine the timing behaviour of software programs embedded in safety-aware real-time systems deployed in various industrial domains including automotive and railway. MBTA methods rely on some form of instrumentation, either at hardware or software level, of the target program or fragments thereof to collect execution-time measurement data. A known drawback of software-level instrumentation is that instrumentation itself does affect the timing and functional behaviour of a program, resulting in the so-called probe effect: leaving the instrumentation code in the final executable can negatively affect average performance and could not be even admissible under stringent industrial qualification and certification standards; removing it before operation jeopardizes the results of timing analysis as the WCET estimates on the instrumented version of the program cannot be valid any more due, for example, to the timing effects incurred by different cache alignments. In this paper, we present a novel approach to mitigate the impact of instrumentation code on cache behaviour by reducing the instrumentation overhead while at the same time preserving and consolidating the results of timing analysis.
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Enrique Díaz, Jaume Abella, Enrico Mezzetti, Irune Agirre, Mikel Azkarate-Askasua, Tullio Vardanega, and Francisco J. Cazorla. Mitigating Software-Instrumentation Cache Effects in Measurement-Based Timing Analysis. In 16th International Workshop on Worst-Case Execution Time Analysis (WCET 2016). Open Access Series in Informatics (OASIcs), Volume 55, pp. 1:1-1:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{diaz_et_al:OASIcs.WCET.2016.1,
  author =	{D{\'\i}az, Enrique and Abella, Jaume and Mezzetti, Enrico and Agirre, Irune and Azkarate-Askasua, Mikel and Vardanega, Tullio and Cazorla, Francisco J.},
  title =	{{Mitigating Software-Instrumentation Cache Effects in Measurement-Based Timing Analysis}},
  booktitle =	{16th International Workshop on Worst-Case Execution Time Analysis (WCET 2016)},
  pages =	{1:1--1:11},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-025-5},
  ISSN =	{2190-6807},
  year =	{2016},
  volume =	{55},
  editor =	{Schoeberl, Martin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2016.1},
  URN =		{urn:nbn:de:0030-drops-68946},
  doi =		{10.4230/OASIcs.WCET.2016.1},
  annote =	{Keywords: WCET, Measurements, Instrumentation overhead}
}
Document
DOI: 10.4230/OASIcs.WCET.2016.9
Measurement-Based Timing Analysis of the AURIX Caches

Authors: Leonidas Kosmidis, Davide Compagnin, David Morales, Enrico Mezzetti, Eduardo Quinones, Jaume Abella, Tullio Vardanega, and Francisco J. Cazorla

Published in: OASIcs, Volume 55, 16th International Workshop on Worst-Case Execution Time Analysis (WCET 2016)

Abstract
Cache memories are one of the hardware resources with higher potential to reduce worst-case execution time (WCET) costs for software programs with tight real-time constraints. Yet, the complexity of cache analysis has caused a large fraction of real-time systems industry to avoid using them, especially in the automotive sector. For measurement-based timing analysis (MBTA) - the dominant technique in domains such as automotive - cache challenges the definition of test scenarios stressful enough to produce (cache) layouts that causing high contention. In this paper, we present our experience in enabling the use of caches for a real automotive application running on an AURIX multiprocessor, using software randomization and measurement-based probabilistic timing analysis (MBPTA). Our results show that software randomization successfully exposes - in the experiments performed for timing analysis - cache related variability, in a manner that can be effectively captured by MBPTA.
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Leonidas Kosmidis, Davide Compagnin, David Morales, Enrico Mezzetti, Eduardo Quinones, Jaume Abella, Tullio Vardanega, and Francisco J. Cazorla. Measurement-Based Timing Analysis of the AURIX Caches. In 16th International Workshop on Worst-Case Execution Time Analysis (WCET 2016). Open Access Series in Informatics (OASIcs), Volume 55, pp. 9:1-9:11, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{kosmidis_et_al:OASIcs.WCET.2016.9,
  author =	{Kosmidis, Leonidas and Compagnin, Davide and Morales, David and Mezzetti, Enrico and Quinones, Eduardo and Abella, Jaume and Vardanega, Tullio and Cazorla, Francisco J.},
  title =	{{Measurement-Based Timing Analysis of the AURIX Caches}},
  booktitle =	{16th International Workshop on Worst-Case Execution Time Analysis (WCET 2016)},
  pages =	{9:1--9:11},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-025-5},
  ISSN =	{2190-6807},
  year =	{2016},
  volume =	{55},
  editor =	{Schoeberl, Martin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2016.9},
  URN =		{urn:nbn:de:0030-drops-69028},
  doi =		{10.4230/OASIcs.WCET.2016.9},
  annote =	{Keywords: WCET, caches, AURIX, Automotive}
}
Document
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.
Cite as

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.
Cite as

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},
  doi =		{10.4230/LITES-v002-i001-a001},
  annote =	{Keywords: Real-time systems, Probabilistic WCET, Randomized caches}
}
Document
DOI: 10.4230/OASIcs.WCET.2012.69
A Time-composable Operating System

Authors: Andrea Baldovin, Enrico Mezzetti, and Tullio Vardanega

Published in: OASIcs, Volume 23, 12th International Workshop on Worst-Case Execution Time Analysis (2012)

Abstract
Time composability is a guiding principle to the development and certification process of real-time embedded systems. Considerable efforts have been devoted to studying the role of hardware architectures - and their modern accelerating features - in enabling the hierarchical composition of the timing behaviour of software programs considered in isolation. Much less attention has been devoted to the effect of real-time Operating Systems (OS) on time composability at the application level. In fact, the very presence of the OS contributes to the variability of the execution time of the application directly and indirectly; by way of its own response time jitter and by its effect on the state retained by the processor hardware. We consider zero disturbance and steady behaviour as those characteristic properties that an operating system should exhibit, so as to be time-composable with the user applications. We assess those properties on the redesign of an ARINC compliant partitioned operating system, for use in avionics applications, and present some experimental results from a preliminary implementation of our approach within the scope of the EU FP7 PROARTIS project.
Cite as

Andrea Baldovin, Enrico Mezzetti, and Tullio Vardanega. A Time-composable Operating System. In 12th International Workshop on Worst-Case Execution Time Analysis. Open Access Series in Informatics (OASIcs), Volume 23, pp. 69-80, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{baldovin_et_al:OASIcs.WCET.2012.69,
  author =	{Baldovin, Andrea and Mezzetti, Enrico and Vardanega, Tullio},
  title =	{{A Time-composable Operating System}},
  booktitle =	{12th International Workshop on Worst-Case Execution Time Analysis},
  pages =	{69--80},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-41-5},
  ISSN =	{2190-6807},
  year =	{2012},
  volume =	{23},
  editor =	{Vardanega, Tullio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2012.69},
  URN =		{urn:nbn:de:0030-drops-35589},
  doi =		{10.4230/OASIcs.WCET.2012.69},
  annote =	{Keywords: Real-time Operating System, Timing composability, ARINC}
}
Document
DOI: 10.4230/OASIcs.WCET.2010.11
Bounding the Effects of Resource Access Protocols on Cache Behavior

Authors: Enrico Mezzetti, Marco Panunzio, and Tullio Vardanega

Published in: OASIcs, Volume 15, 10th International Workshop on Worst-Case Execution Time Analysis (WCET 2010)

Abstract
The assumption of task independence has long been consubstantial with the formulation of many schedulability analysis techniques. That assumption is evidently advantageous for the mathematical formulation of the analysis equations, but ill fit to capture the actual behavior of the system. Resource sharing is one of the system design dimensions that break the assumption of task independence. By shaking the very foundations of the real-time analysis theory, the advent of multicore systems has caused resurgence of interest in resource sharing and synchronization protocols, and also dawned the fact that the assumption of task independence may be forever broken. Research in cache-aware schedulability analysis instead has paid very little attention to the impact that synchronization protocols may have on cache behavior. A blocked task may in fact incur time penalties similar in kind to those caused by preemption, in that some useful code or data already loaded in the cache may be evicted while the task is blocked. In this paper we characterize the sources of cache-related blocking delay (CRBD). We then provide a bound on the CRBD for three synchronization protocols of interest. The comparison between these bounds provides striking evidence that an informed choice of the synchronization protocol helps contain the perturbing effects of blocking on the cache state.
Cite as

Enrico Mezzetti, Marco Panunzio, and Tullio Vardanega. Bounding the Effects of Resource Access Protocols on Cache Behavior. In 10th International Workshop on Worst-Case Execution Time Analysis (WCET 2010). Open Access Series in Informatics (OASIcs), Volume 15, pp. 11-22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{mezzetti_et_al:OASIcs.WCET.2010.11,
  author =	{Mezzetti, Enrico and Panunzio, Marco and Vardanega, Tullio},
  title =	{{Bounding the Effects of Resource Access Protocols on Cache Behavior}},
  booktitle =	{10th International Workshop on Worst-Case Execution Time Analysis (WCET 2010)},
  pages =	{11--22},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-21-7},
  ISSN =	{2190-6807},
  year =	{2010},
  volume =	{15},
  editor =	{Lisper, Bj\"{o}rn},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2010.11},
  URN =		{urn:nbn:de:0030-drops-28217},
  doi =		{10.4230/OASIcs.WCET.2010.11},
  annote =	{Keywords: Resource access protocols, cache, worst-case response time}
}
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