May 20 - José Marinho, ISEP, Portugal - On Preemption Delay and WCET handling on Reservation frameworks¶

Talk abstract: The demand for time predictability on real-time systems has been addressed, in practice, by overallocation of resources to overcome the non-determinism present in code execution. With the evolution of microprocessor architecture technology, this scenario tends to move in the direction of having even more waste due to the inefficient usage of several architectural constructs geared towards the minimisation of average case execution times. This talk will cover the problem of efficient usage of caches in a multi-task preemptive system. Due to the ever increasing processor memory gap, the amount of knowledge on the cache state available on the system, has a strong impact on the resource allocation decisions taken. Some cache related preemption delay algorithms will be presented along with a method for managing CRPD on run-time.

Speaker Bio.: José Marinho is an Electrical Engineer from the University of Coimbra. While studying for his degree, José became interested in processor architectures and real-time systems. After a year working in robotics (ISR-Coimbra), José finally moved into ISEP's CISTER unit to carry out his PhD studies in real-time systems.

Papers: Tightening the Bounds on Feasible Preemption Points (pdf), The Worst-Case Execution Time Problem - overview of methods and survey of tools (pdf), Preemption Points Placement for Sporadic Tasks (pdf), A New Notion of Useful Cache Block to Improve the Bounds of Cache-Related Preemption Delay (pdf),Scalable Precision Cache Analysis for Real-Time Software (pdf) Scheduling Real-Time Applications in an Open Environment (pdf) Bounding Cache-Related Preemption Delay for Real-Time Systems (pdf) Bounding Preemption Delay within Data Cache Reference Patterns for Real-Time Tasks (pdf) Accurate Estimation of Cache-Related Preemption Delay (pdf)


Talk slides: pdf

June 4 - Claro Noda, ISEP, Portugal - Fine-grained network time synchronization using reference broadcasts¶

Talk abstract:Recent advances in miniaturization and low-cost, low-power design have led to active research in large-scale networks of small, wireless, low-power sensors and actuators. Time synchronization is critical in sensor networks for diverse purposes including sensor data fusion, coordinated actuation, and power-efficient duty cycling. Though the clock accuracy and precision requirements are often stricter than in traditional distributed systems, strict energy constraints limit the resources available to meet these goals.We present Reference-Broadcast Synchronization, a scheme in which nodes send reference beacons to their neighbors using physical-layer broadcasts. A reference broadcast does not contain an explicit timestamp; instead, receivers use its arrival time as a point of reference for comparing their clocks. In this paper, we use measurements from two wireless implementations to show that removing the sender's nondeterminism from the critical path in this way produces high-precision clock agreement (1.85 ± 1.28μsec, using off-the-shelf 802.11 wireless Ethernet), while using minimal energy. We also describe a novel algorithm that uses this same broadcast property to federate clocks across broadcast domains with a slow decay in precision (3.68 ± 2.57μsec after 4 hops). RBS can be used without external references, forming a precise relative timescale, or can maintain microsecond-level synchronization to an external timescale such as UTC. We show a significant improvement over the Network Time Protocol (NTP) under similar conditions.

Speaker Bio.:Claro Noda graduated in Physics from University of Havana, Cuba in 1996. He worked in Scientific Instrumentation at the Superconductivity Laboratory, IMRE (1996-2001) where he completed his Master in Physical Sciences in 2000 and later continued research activities at the "Henri Poincaré" Complex Systems Group. He has also taught at the General Physics Department in the Faculty of Physics in Havana (2005-2008). Currently he's a MAP-Tele PhD student at University of Minho and a researcher at CISTER/ISEP, Portugal.

Paper: Fine-grained network time synchronization using reference broadcasts (pdf)

July 2 - Ricardo Garibay-Martínez, ISEP, Portugal - Integrating Multimedia Applications in Hard Real-Time Systems¶

Talk abstract:This paper focuses on the problem of providing efficient run-time support to multimedia applications in a real-time system, where two types of tasks can coexist simultaneously: multimedia soft real-time tasks and hard real-time tasks. Hard tasks are guaranteed based on worst case execution times and minimum interarrival times, whereas multimedia and soft tasks are served based on mean parameters. The paper describes a server-based mechanism for scheduling soft and multimedia tasks without jeopardizing the a priori guarantee of hard real-time activities. The performance of the proposed method is compared with that of similar service mechanisms through extensive simulation experiments and several multimedia applications have been implemented on the HARTIK kernel.

Speaker Bio.: Ricardo received his Bachelors Degree from Morelia Institute of Technology (ITM) in 2007 and finished his Master of Science in Computer Science from Centre for Scientific Research and Higher Education of Ensenada (CICESE), Mexico. He has experience working as a lecturer and as a researcher for PEMEX Petroleum Company. Since 2007, he has been working in the area of Adaptive Resource Management in Distributed Dynamic Real-Time Systems. Currently, he is working as a researcher and PhD student in CISTER/IPP-HURRAY Research unit. His current research interests are Adaptive RT Systems, RT Software and Multi-core Systems.

Paper: Integrating Multimedia Applications in Hard Real-Time Systems (pdf)


Talk slides: pdf

July 9 - Artem Burmyakov, ISEP, Portugal - Techniques for Multiprocessor Global Schedulability Analysis¶

Talk Abstract: The scheduling of sporadic task systems upon multiprocessor platforms is considered, when inter-processor migration is permitted. It is known that current schedulability tests for such systems perform quite poorly when compared to schedulability tests for partitioned scheduling. Limitations of current tests are identified, which may be responsible for the unsatisfactory performance of these tests. A new test that overcomes some of these limitations is proposed and proved correct.

Speaker Bio.: Artem Burmyakov received a masters' degree in Computer Sciences from Moscow Engineering and Physics Institute. He worked as a software engineer within CERN for more than 4 years, participating in the LHC GCS and the UAB projects. Nowadays he is a doctoral student within CISTER. His professional interests are related to the development of control, real-time and distributed systems.

Paper: Techniques for Multiprocessor Global Schedulability Analysis (pdf)


Talk slides: pdf

July 16 - Maryam Vahabi, ISEP, Portugal - Wireless Sensor Networks for Habitat Monitoring¶

Talk Abstract: We provide an in-depth study of applying wireless sensor networks to real-world habitat monitoring. A set of system design requirements are developed that cover the hardware design of the nodes, the design of the sensor network, and the capabilities for remote data access and management. A system architecture is proposed to address these requirements for habitat monitoring in general, and an instance of the architecture for monitoring seabird nesting environment and behavior is presented. The currently deployed network consists of 32 nodes on a small island off the coast of Maine streaming useful live data onto the web. The application driven design exercise serves to identify important areas of further work in data sampling, communications, network re-tasking, and health monitoring.

Speaker Bio.: Maryam Vahabi received her degree in Electrical Engineering from University of Guilan in 2003. She obtained her Master of Science in Communication Network Engineering from University Putra Malaysia in 2009 and her Master research was on wireless sensor networks. She has joined the IPP-HURRAY! in July, 2009. Currently, she is doing her PhD in CISTER/IPP-HURRAY Research unit.Her current research interests are sensor networks, real-time systems and schedulability analysis.

Paper: Wireless Sensor Networks for Habitat Monitoring (pdf)


Talk slides: pdf

July 23 - Dakshina Dasari, ISEP, Portugal - Bounds on Multiprocessing Timing Anomalies¶

Talk Abstract: A multiprocessing system consisting of many identical processors acting in parallel may exhibit certain somewhat unexpected "anomalies," even though the system operates under a rather natural set of rules; e.g., it can happen that increasing the number of processors can increase the length of time required to execute a given set of tasks. In this talk we will study a typical model of such a multiprocessing system, see some examples of such anomalies and determine the precise extent by which the execution time for a set of tasks can be influenced because of these timing anomalies.

Speaker Bio.: Dakshina Dasari was born in 1980 in India. She has a Bachelors Degree from Karnataka University Dharwad and finished her Masters in 2004 from National Institute of Technology, Surathkal (NITK), India. She has five years of working experience - 3 yrs at Sun Microsystems and 2 yrs at Citrix Pvt Ltd as Software Engineer. She has previously worked in the area of Networking.

Paper: Bounds on Multiprocessing Timing Anomalies (pdf)


Talk slides: pdf

September 17 - José Marinho, ISEP, Portugal - Integrated Resource Management and Scheduling with Multi-Resource Constraints¶

Talk abstract: Dynamic real-time systems such as phased-array radars must manage multiple resources, satisfy energy constraints and make frequent on-line scheduling decisions. These systems are hard to manage because task and system requirements change rapidly (e.g. in radar systems, the targets/tasks in the sky are moving continuously) and must satisfy a multitude of constraints. Their highly dynamic nature and stringent time constraints lead to complex cross-layer interactions in these systems. Therefore, the design of such systems has long been a conservative and/or unpredictable mixture of pre-computed schedules, pessimistic resource allocations, cautious energy usage and operator intuition. In this paper, we present an integrated approach that simultaneously maximizes overall system utility, performs task scheduling and satisfies multi-resource constraints. Using a phased-array radar system, we show that our approach can reconfigure settings of 100 tracks at every 0.7 sec in real-time, and performs within 0.1% of the achievable optimal solution.

Speaker Bio.: José Marinho is an Electrical Engineer from the University of Coimbra. While studying for his degree, José became interested in processor architectures and real-time systems. After a year working in robotics (ISR-Coimbra), José finally moved into ISEP's CISTER unit to carry out his PhD studies in real-time systems.

Paper:Integrated Resource Management and Scheduling with Multi-Resource Constraints (pdf)

September 24 - Paulo Baltarejo Sousa, ISEP, Portugal - Scheduling Algorithms for Multiprocessors in a Hard Real-Time Environment¶

Talk abstract: The problem of multiprogramming scheduling on a single processor is studied from the viewpoint of the characteristics peculiar to the program functions that need guaranteed service. It is shown that an optimum fixed priority scheduler possesses an upper bound to processor utilization which may be as low as 70 percent for large task sets. It is also shown that full processor utilization can be achieved by dynamically assigning priorities on the basis of their current deadlines. A combination of these two scheduling techniques is also discussed.

Speaker Bio.: Paulo Baltarejo Sousa is a researcher on scheduling algorithms for Multicore processors at CISTER Research Group and also a Lecturer at the Polytechnic Institute of Porto.

Paper: available at Delft \Project\FCT\RESCORE\scientific_literature\papers\multipro\Liu69_global_static_prio

Talk slides: pdf

October 8 - António Barros, ISEP, Portugal - Programming Execution-Time Servers in Ada 2005¶

Talk abstract: Much of the research on scheduling schemes is prevented from being used in practice by the lack of implementations that provide the necessary abstractions. An example of this is the support of execution-time servers. Apart for a single mechanism (the Sporadic Server), which is defined in the POSIX standard, these important building blocks are not available to the system developer. Over the last few years, we have been developing the mechanisms necessary to construct execution-time servers from within an Ada context. Versions of these have now been incorporated in the Ada 2005 standard. In this paper, we show how the mechanisms can be used to construct the Deferrable and Sporadic servers

Speaker Bio.: António Manuel de Sousa Barros was born in 1974 and has a degree (1997) in Electrical and Computer Engineering at the Universtity of Porto. Since 2001 he has been a teacher assistant at the Department of Computer Engineering, among other radical sports. He was researcher at the Biomedical Engineering Institute (University of Porto) from 1998 to 2001. He also worked as freelancer in the fields of electronics and computer programming. Since January 2005 he is also with the IPP-HURRAY. His interests are in electronic devices communications, data acquisition, signal processing.

Paper: Programming Execution-Time Servers in Ada 2005 (pdf)

Talk slides: pdf

October 22 - Muhammad Ali Awan, ISEP, Portugal - Improving Soft Real-Time Performance Through Better Slack Reclaiming¶

Talk abstract: Modern operating systems frequently support applications with a variety of timing constraints including hard real-time, soft real-time, and best-effort. To guarantee performance, critical applications typically over-reserve resources based on worst-case resource usage estimates, while others may reserve based on average-case or other estimates. When resources are fully subscribed, the performance of soft- and non-real-time applications depends upon the effective distribution of dynamic slack—reserved, but unused resources—from other tasks. Motivated by several representative examples, we derive four general principles for the effective management of slack. We have implemented these principles in four progressively better slack schedulers that demonstrate their effectiveness. BACKSLASH, which employs all four principles, misses fewer soft realtime deadlines than all of the other slack schedulers we examined

Speaker Bio.: Muhammad Ali Awan did his master's Degree from Royal Institute of Technology(KTH) Sweden in System on Chip Design with a focus on Digital System Design and Embedded Systems. He worked as Lecturer in National University of Science and Technology Pakistan. He also worked as a researcher in IMEC, Belgium for two years. His research focus was on High Level Memory Management. Currently he started his PhD in CISTER and participating in a research on "Real-Time Power Management on Partitioned Multicores"

Paper: Improving Soft Real-Time Performance Through Better Slack Reclaiming (pdf)

Talk slides: pdf

October 29 - Gurulingesh Raravi, ISEP, Portugal - Multiprocessor On-Line Scheduling of Hard-Real-Time Tasks¶

Talk abstract: The problems of hard-real-time task scheduling in a multiprocessor environment are discussed in terms of a scheduling game representation of the problem. It is shown that optimal scheduling without a priori knowledge is impossible in the multiprocessor case even if there is no restriction on preemption owing to precedence or mutual exclusion constraints. Sufficient conditions are derived which will permit a set of tasks to be optimally scheduled at run time.

Speaker Bio.: Gurulingesh Raravi did his Bachelors in Computer Science and Engineering from Karnataka University Dharwad and finished his Masters in Information Technology at IIT Bombay in 2005. He has three years of working experience. Currently, he is doing PhD in the area of Heterogeneous Multi-core Real-Time Scheduling.

Paper: Multiprocessor On-Line Scheduling of Hard-Real-Time Tasks (pdf)

Talk slides: pdf

November 12 - Ricardo Severino, ISEP, Portugal - Computing Needs Time¶

Talk abstract: This paper considers the orchestration of computing with physical processes. It argues that to realize its full potential, the core abstractions of computing need to be rethought to incorporate ssential properties of the physical systems, most particularly the passage of time. It makes a case that the solution cannot be simply overlaid on existing abstractions, and outlines a number of promising approaches being pursued. The emphasis needs to be on repeatable behavior rather than on performance optimization.

Speaker Bio.: Ricardo Severino was born in 1982 and has a Degree (2006), and a MSc (2008) in Electrical and Computer Engineering at the Polytechnic Institute of Porto – School of Engineering (ISEP/IPP). Since 2006, he has been working in the area of Wireless Sensor Networks, namely on improving quality-of-service (QoS) in WSNs by using standard and commercial-off-the-shelf (COTS) technology, at the CISTER/IPP-HURRAY! Research Unit. In this line, he has been actively participating in the ART-WiSe (http://artwise.cister-isep.info) and Open-ZB (http://www.open-zb.net) research frameworks, as well as in international projects such as ArtistDesign (FP7 NoE on Embedded System Design), CONET (FP7 NoE on Cooperating Objects), and EMMON (FP7 JU on Embedded Monitoring). He is also a founding member and contributor of the 15.4 and ZigBee TinyOS Working Groups. Recently, his MSc Thesis work was awarded with the EWSN'09 Best MSc Thesis Award at the prestigious European Conference on Wireless Sensor Networks (EWSN'09). He has several publications in reputed conferences (e.g. MASS, RTCSA, ECRTS) and journals (e.g. IEEE TII) and has served as a reviewer for several conferences (e.g. IEEE ETFA, SUTC and VTC).

Paper: Computing Needs Time (pdf)

Talk slides: pdf

November 19 - Aida Ehyaei, ISEP, Portugal - Towards Controllable Distributed Real-Time Systems with Feasible Utilization Control¶

Talk abstract: Feedback control techniques have recently been applied to a variety of real-time systems. However, a fundamental issue that was left out is guaranteeing system controllability and the feasibility of applying feedback control to such systems. No control algorithms can effectively control a system which itself is uncontrollable or infeasible. In this paper, we use the multiprocessor utilization control problem as a representative example to study the controllability and feasibility of distributed real-time systems. We prove that controllability and feasibility of a system depend crucially on end-to-end task allocations. We then present algorithms for deploying end-to-end tasks to ensure that the system is controllable and utilization control is feasible for the system. Furthermore, we develop runtime algorithms to maintain controllability and feasibility by reallocating tasks dynamically in response to workload variations, such as task terminations and migrations caused by processor failures. We implement our algorithms in a robust real-time middleware system and report empirical results on an experimental test-bed. We also evaluate the performance of our approach in large systems using numerical experiments. Our results demonstrate that the proposed task allocation algorithms improve the robustness of feedback control in distributed real-time systems.

Speaker Bio.: Aida Ehyaei received her MSc. and BSc. degree in Electrical engineering from Isfahan University of technology, Iran. She is a PhD student in FEUP and does her research in Cister research Unit from September 2009. Her current research activity is in the field of Cyber Physical Systems.

Paper: Towards Controllable Distributed Real-Time Systems with Feasible Utilization Control(pdf)

Talk slides: pdf

November 26 - Hossein Fotouhi, ISEP, Portugal - Emerging Challenges: Mobile Networking for Smart Dust¶

Talk abstract: Large-scale networks of wireless sensors are becoming increasingly tractable. Advances in hardware technology and engineering design have led to dramatic reductions in size, power consumption and cost for digital circuitry, wireless communications and Micro ElectroMechanical Systems (MEMS). This has enabled very compact, autonomous and mobile nodes, each containing one or more sensors, computation and communication capabilities, and a power supply. The missing ingredient is the networking and applications layers needed to harness this revolutionary capability into a complete system. We review the key elements of the emergent technology of “Smart Dust” and outline the research challenges they present to the mobile networking and systems community, which must provide coherent connectivity to large numbers of mobile network nodes co-located within a small volume.

Speaker Bio.: Hossein Fotouhi received his degree on Electrical Electronics Engineering in 2004 and worked afterwards for about three years. He obtained his Master of Science in Communication Network Engineering in 2009. His MSc thesis was on "optimizing energy consumption in MAC layer for Wireless Sensor Networks". Currently, he is doing his PhD research in CISTER Research Unit since July 2009. His research interests are wireless sensor networks, mobility management, handoff mechanism and fuzzy logic theory.

Paper: Emerging Challenges: Mobile Networking for Smart Dust(pdf)

Talk slides: pdf

December 10; 13:00 hrs - Borislav Nikolic, ISEP, Portugal - The Multikernel: A new OS architecture for scalable multicore systems¶

Talk abstract: Commodity computer systems contain more and more processor cores and exhibit increasingly diverse architectural tradeoffs, including memory hierarchies, interconnects, instruction sets and variants, and IO configurations. Previous high-performance computing systems have scaled in specific cases, but the dynamic nature of modern client and server workloads, coupled with the impossibility of statically optimizing an OS for all workloads and hardware variants pose serious challenges for operating system structures. The paper is joint project of ETH Zurich and Microsoft Research. The authors argue that the challenge of future multicore hardware is best met by embracing the networked nature of the machine, rethinking OS architecture using ideas from distributed systems. They investigate a new OS structure, the multikernel, that treats the machine as a network of independent cores, assumes no inter-core sharing at the lowest level, and moves traditional OS functionality to a distributed system of processes that communicate via message-passing. Also, they have implemented a multikernel OS to show that the approach is promising, and they describe how traditional scalability problems for operating systems (such as memory management) can be effectively recast using messages and can exploit insights from distributed systems and networking. An evaluation of our prototype on multicore systems shows that, even on present-day machines, the performance of a multikernel is comparable with a conventional OS, and can scale better to support future hardware.

Speaker Bio.: Borislav graduated at the Faculty of Electrical Engineering in Belgrade with major in Computer Science in 2007. He spent almost two years in industry developing large-scale enterprise applications. Currently, Borislav is doing his PhD at CISTER/IPP-HURRAY Research unit. He is amateur road cyclist and big fan of FC Red Star Belgrade. His research interests include real time and embedded systems, distributed and parallel computing, gossip protocols, ORMs and software architecture and design.