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Documents authored by Abella, Jaume

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.
Cite as

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.
Cite as

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.
Cite as

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.
Cite as

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/LIPIcs.ECRTS.2018.3
HWP: Hardware Support to Reconcile Cache Energy, Complexity, Performance and WCET Estimates in Multicore Real-Time Systems

Authors: Pedro Benedicte, Carles Hernandez, Jaume Abella, and Francisco J. Cazorla

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

Abstract
High-performance processors have deployed multilevel cache (MLC) systems for decades. In the embedded real-time market, the use of MLC is also on the rise, with processors for future systems in space, railway, avionics and automotive already featuring two or more cache levels. One of the most critical elements for MLC is the write policy that not only affects several key metrics such as performance, WCET estimates, energy/power, and reliability, but also the design of complexity-prone cache coherence protocol and cache reliability solutions. In this paper we make an extensive analysis of existing write policies, namely write-through (WT) and write-back (WB). In the context of the real-time domain, we show that no write policy is superior for all metrics: WT simplifies the design of the coherence and reliability solutions at the cost of performance, WCET, and energy; while WB improves performance and energy results, but complicates cache design. To take the best of each policy, we propose Hybrid Write Policy (HWP) a low-complexity hardware mechanism that reconciles the benefits of WT in terms of simplifying the cache design (e.g. coherence solution) and the benefits of WB in improved average performance and WCET estimates as the pressure on the interconnection network increases. Guaranteed performance results show that HWP scales with core count similar to WB. Likewise, HWP reduces cache energy usage of WT, to levels similar to those of WB. These benefits are obtained while retaining the reduced coherence complexity of WT, in contrast to high coherence costs under WB.
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Pedro Benedicte, Carles Hernandez, Jaume Abella, and Francisco J. Cazorla. HWP: Hardware Support to Reconcile Cache Energy, Complexity, Performance and WCET Estimates in Multicore Real-Time Systems. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 3:1-3:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{benedicte_et_al:LIPIcs.ECRTS.2018.3,
  author =	{Benedicte, Pedro and Hernandez, Carles and Abella, Jaume and Cazorla, Francisco J.},
  title =	{{HWP: Hardware Support to Reconcile Cache Energy, Complexity, Performance and WCET Estimates in Multicore Real-Time Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{3:1--3:22},
  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.2018.3},
  URN =		{urn:nbn:de:0030-drops-90005},
  doi =		{10.4230/LIPIcs.ECRTS.2018.3},
  annote =	{Keywords: multilevel caches, real-time systems, multicores, WCET}
}
Document
DOI: 10.4230/LIPIcs.ECRTS.2017.16
Design and Implementation of a Time Predictable Processor: Evaluation With a Space Case Study

Authors: Carles Hernández, Jaume Abella, Francisco J. Cazorla, Alen Bardizbanyan, Jan Andersson, Fabrice Cros, and Franck Wartel

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

Abstract
Embedded real-time systems like those found in automotive, rail and aerospace, steadily require higher levels of guaranteed computing performance (and hence time predictability) motivated by the increasing number of functionalities provided by software. However, high-performance processor design is driven by the average-performance needs of mainstream market. To make things worse, changing those designs is hard since the embedded real-time market is comparatively a small market. A path to address this mismatch is designing low-complexity hardware features that favor time predictability and can be enabled/disabled not to affect average performance when performance guarantees are not required. In this line, we present the lessons learned designing and implementing LEOPARD, a four-core processor facilitating measurement-based timing analysis (widely used in most domains). LEOPARD has been designed adding low-overhead hardware mechanisms to a LEON3 processor baseline that allow capturing the impact of jittery resources (i.e. with variable latency) in the measurements performed at analysis time. In particular, at core level we handle the jitter of caches, TLBs and variable-latency floating point units; and at the chip level, we deal with contention so that time-composable timing guarantees can be obtained. The result of our applied study with a Space application shows how per-resource jitter is controlled facilitating the computation of high-quality WCET estimates.
Cite as

Carles Hernández, Jaume Abella, Francisco J. Cazorla, Alen Bardizbanyan, Jan Andersson, Fabrice Cros, and Franck Wartel. Design and Implementation of a Time Predictable Processor: Evaluation With a Space Case Study. In 29th Euromicro Conference on Real-Time Systems (ECRTS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 76, pp. 16:1-16:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{hernandez_et_al:LIPIcs.ECRTS.2017.16,
  author =	{Hern\'{a}ndez, Carles and Abella, Jaume and Cazorla, Francisco J. and Bardizbanyan, Alen and Andersson, Jan and Cros, Fabrice and Wartel, Franck},
  title =	{{Design and Implementation of a Time Predictable Processor: Evaluation With a Space Case Study}},
  booktitle =	{29th Euromicro Conference on Real-Time Systems (ECRTS 2017)},
  pages =	{16:1--16:23},
  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.2017.16},
  URN =		{urn:nbn:de:0030-drops-71737},
  doi =		{10.4230/LIPIcs.ECRTS.2017.16},
  annote =	{Keywords: Processor design, performance guarantees, multicore, Industrial case studies, Application of real-time technology in realistic systems}
}
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.
Cite as

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.
Cite as

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/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.2014.31
Contention in Multicore Hardware Shared Resources: Understanding of the State of the Art

Authors: Gabriel Fernandez, Jaume Abella, Eduardo Quiñones, Christine Rochange, Tullio Vardanega, and Francisco J. Cazorla

Published in: OASIcs, Volume 39, 14th International Workshop on Worst-Case Execution Time Analysis (2014)

Abstract
The real-time systems community has over the years devoted considerable attention to the impact on execution timing that arises from contention on access to hardware shared resources. The relevance of this problem has been accentuated with the arrival of multicore processors. From the state of the art on the subject, there appears to be considerable diversity in the understanding of the problem and in the "approach" to solve it. This sparseness makes it difficult for any reader to form a coherent picture of the problem and solution space. This paper draws a tentative taxonomy in which each known approach to the problem can be categorised based on its specific goals and assumptions.
Cite as

Gabriel Fernandez, Jaume Abella, Eduardo Quiñones, Christine Rochange, Tullio Vardanega, and Francisco J. Cazorla. Contention in Multicore Hardware Shared Resources: Understanding of the State of the Art. In 14th International Workshop on Worst-Case Execution Time Analysis. Open Access Series in Informatics (OASIcs), Volume 39, pp. 31-42, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{fernandez_et_al:OASIcs.WCET.2014.31,
  author =	{Fernandez, Gabriel and Abella, Jaume and Qui\~{n}ones, Eduardo and Rochange, Christine and Vardanega, Tullio and Cazorla, Francisco J.},
  title =	{{Contention in Multicore Hardware Shared Resources: Understanding of the State of the Art}},
  booktitle =	{14th International Workshop on Worst-Case Execution Time Analysis},
  pages =	{31--42},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-69-9},
  ISSN =	{2190-6807},
  year =	{2014},
  volume =	{39},
  editor =	{Falk, Heiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2014.31},
  URN =		{urn:nbn:de:0030-drops-46027},
  doi =		{10.4230/OASIcs.WCET.2014.31},
  annote =	{Keywords: Contention, Multicores, WCET Analysis}
}
Document
DOI: 10.4230/OASIcs.WCET.2013.64
Upper-bounding Program Execution Time with Extreme Value Theory

Authors: Francisco J. Cazorla, Tullio Vardanega, Eduardo Quiñones, and Jaume Abella

Published in: OASIcs, Volume 30, 13th International Workshop on Worst-Case Execution Time Analysis (2013)

Abstract
In this paper we discuss the limitations of and the precautions to account for when using Extreme Value Theory (EVT) to compute upper bounds to the execution time of programs. We analyse the requirements placed by EVT on the observations to be made of the events of interest, and the conditions that render safe the computations of execution time upper bounds. We also study the requirements that a recent EVT-based timing analysis technique, Measurement-Based Probabilistic Timing Analysis (MBPTA), introduces, besides those imposed by EVT, on the computing system under analysis to increase the trustworthiness of the upper bounds that it computes.
Cite as

Francisco J. Cazorla, Tullio Vardanega, Eduardo Quiñones, and Jaume Abella. Upper-bounding Program Execution Time with Extreme Value Theory. In 13th International Workshop on Worst-Case Execution Time Analysis. Open Access Series in Informatics (OASIcs), Volume 30, pp. 64-76, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

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@InProceedings{cazorla_et_al:OASIcs.WCET.2013.64,
  author =	{Cazorla, Francisco J. and Vardanega, Tullio and Qui\~{n}ones, Eduardo and Abella, Jaume},
  title =	{{Upper-bounding Program Execution Time with Extreme Value Theory}},
  booktitle =	{13th International Workshop on Worst-Case Execution Time Analysis},
  pages =	{64--76},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-54-5},
  ISSN =	{2190-6807},
  year =	{2013},
  volume =	{30},
  editor =	{Maiza, Claire},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2013.64},
  URN =		{urn:nbn:de:0030-drops-41232},
  doi =		{10.4230/OASIcs.WCET.2013.64},
  annote =	{Keywords: WCET, Extreme Value Theory, Probabilistic, Deterministic}
}
Document
DOI: 10.4230/OASIcs.WCET.2013.97
Applying Measurement-Based Probabilistic Timing Analysis to Buffer Resources

Authors: Leonidas Kosmidis, Tullio Vardanega, Jaume Abella, Eduardo Quiñones, and Francisco J. Cazorla

Published in: OASIcs, Volume 30, 13th International Workshop on Worst-Case Execution Time Analysis (2013)

Abstract
The use of complex hardware makes it difficult for current timing analysis techniques to compute trustworthy and tight worst-case execution time (WCET) bounds. Those techniques require detailed knowledge of the internal operation and state of the platform, at both the software and hardware level. Obtaining that information for modern hardware platforms is increasingly difficult. Measurement-Based Probabilistic Timing Analysis (MBPTA) reduces the cost of acquiring the knowledge needed for computing trustworthy and tight WCET bounds. MBPTA based on Extreme Value Theory requires the execution time of processor instructions to be independent and identically distributed (i.i.d.), which can be achieved with some hardware support. Previous proposals show how those properties can be achieved for caches. This paper considers, for the first time, the implications on MBPTA of using buffer resources. Buffers in general, and first-come first-served (FCFS) buffers in particular, are of paramount importance as the complexity of hardware increases, since they allow managing contention in those resources where multiple requests may be pending. We show how buffers can be used in the context of MBPTA and provide illustrative examples.
Cite as

Leonidas Kosmidis, Tullio Vardanega, Jaume Abella, Eduardo Quiñones, and Francisco J. Cazorla. Applying Measurement-Based Probabilistic Timing Analysis to Buffer Resources. In 13th International Workshop on Worst-Case Execution Time Analysis. Open Access Series in Informatics (OASIcs), Volume 30, pp. 97-108, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

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@InProceedings{kosmidis_et_al:OASIcs.WCET.2013.97,
  author =	{Kosmidis, Leonidas and Vardanega, Tullio and Abella, Jaume and Qui\~{n}ones, Eduardo and Cazorla, Francisco J.},
  title =	{{Applying Measurement-Based Probabilistic Timing Analysis to Buffer Resources}},
  booktitle =	{13th International Workshop on Worst-Case Execution Time Analysis},
  pages =	{97--108},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-54-5},
  ISSN =	{2190-6807},
  year =	{2013},
  volume =	{30},
  editor =	{Maiza, Claire},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WCET.2013.97},
  URN =		{urn:nbn:de:0030-drops-41269},
  doi =		{10.4230/OASIcs.WCET.2013.97},
  annote =	{Keywords: WCET, Buffer, Probabilistic Timing Analysis}
}
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