Laurent George - Academia.edu (original) (raw)

Papers by Laurent George

Scheduling theory, as it applies to hard-real-time environment, has been widely studied in the la... more Scheduling theory, as it applies to hard-real-time environment, has been widely studied in the last twenty years and it might be unclear to make it out within the plethora of results available. Our goal is first to collect in a single paper the results known for uniprocessor, non-idling, preemptive/non-preemptive, fixed/dynamic priority driven contexts, considering general task sets as a central figure for the description of possible processor loads. Second to establish new results when needed. In particular, optimality, feasibility conditions and worst-case response times are examined largely by utilizing the concepts of workload, processor demand and busy period. Some classic extensions such as jitter, resource sharing are also considered. Although this work is not oriented toward a formal comparison of these results, it appears that preemptive and non-preemptive scheduling are closely related and that the analysis of fixed versus dynamic scheduling might be unified according to the concept of higher priority busy period. In particular, we introduce the notion of deadline-d busy period for EDF schedules, that we conjecture to be an interesting parallel of the level-i busy period, a concept already used in the analysis of fixed priority driven scheduling.

We focus on the partitioned scheduling of sporadic real-time tasks with constrained deadlines. Th... more We focus on the partitioned scheduling of sporadic real-time tasks with constrained deadlines. The scheduling policy on each processor is staticpriority. The considered tasks are not independent and the consistency of these shared data is ensured by a multiprocessor synchronization protocol. Considering these assumptions, we propose a partitioned scheduling algorithm which tends to maximize the robustness of the tasks to the Worst Case Execution Time (WCET) overruns faults. We describe the context of the problem and we outline our solution based on simulated annealing.

ABSTRACT Real-time industrial domains are subject to strong constraints in terms of performance a... more ABSTRACT Real-time industrial domains are subject to strong constraints in terms of performance and reliability that directly increase the costs of their infrastructures. In order to build these infrastructures and to test them, we propose to implement ARTEMIS: Another Real-Time Engine for Message-Issued Sim- ulation. Its aim is to manage all real-time networks like CAN or AFDX and to simulate their behaviors in terms of scheduling and performance delay. To implement this tool, we use a modular way of development, building modules on a two-parts kernel. This architecture allows our software to be generic. Moreover, many interfaces can be easily integrated for several network implementations.

Our paper deals with a Dynamic Spectrum Access (DSA) and its implementation on a Software Defined... more Our paper deals with a Dynamic Spectrum Access (DSA) and its implementation on a Software Defined Radio (SDR) for IEEE 802.15.4e Networks. The network nodes select the carrier frequency after Energy-Detection based Spectrum Sensing (SS). To ensure frequency hoping between two nodes in IEEE 802.15.4e Network, we propose a synchronization algorithm. We considerate the IEEE 802.15.4e Network is Secondary User (SU), and all other networks are Primary Users (PUs) in unlicensed 868/915 MHz and 2450 MHz bands of a Cognitive Radio (CR). However, the algorithm and the energy-sensor have been implemented over GNU Radio and Universal Software Radio Peripheral (USRP) SDR. In addition, real packet transmissions have been performed in two cases. In the first case, SU communicates in static carrier-frequency, while in the second case with the implemented DSA. For each case, PU transmitter disturbs SU, which calculates Packet Success Rate (PSR) to measure the robustness of a used DSA. The obtained PSR is improved by 80\% when the SU accomplished DSA rather than a static access.

ABSTRACT In this paper, we focus on real-time switched Ether- net networks with mixed-criticality... more ABSTRACT In this paper, we focus on real-time switched Ether- net networks with mixed-criticality constraints. We are interested in (i) exploiting IEEE 1588 Precision Time Protocol (PTP) to implement criticality propagation techniques in such networks and (ii) analyzing delay of criticality switching. This work presents how to inte- grate criticality concepts for messages sent on Ethernet networks using PTP protocol. Concerning the delay of criticality switching, we consider FIFO and Fixed- Priority scheduling policies.

2015 IEEE 18th International Symposium on Real-Time Distributed Computing, 2015

Leveraging Applications of Formal Methods, 2007

Journal of Aerospace Computing, Information, and Communication, 2009

2007 IEEE Conference on Emerging Technologies & Factory Automation (EFTA 2007), 2007

In this paper, we propose to extend real-time feasibility conditions taking into account kernel o... more In this paper, we propose to extend real-time feasibility conditions taking into account kernel overheads for mixed preemptive periodic tasks with shared resources when tasks are scheduled with fixed priority FP/FIFO scheduling, where FIFO is used to arbitrate tasks having the same fixed priority. The kernel considered in this paper is an event driven OSEK kernel which uses the priority

Proceedings of the 8th international conference on New technologies in distributed systems - NOTERE '08, 2008

In this paper, we study the problem of maintaining the consistency of distributed objects in real... more In this paper, we study the problem of maintaining the consistency of distributed objects in real-time. Sporadic transactions sent by a set of clients must be processed by a set servers with a bounded end-to-end response time. We propose in this article a solution, following the state machine approach, based on a particular non-preemptive scheduling denoted EDF* (Earliest Deadline First

Proceedings of 2012 IEEE 17th International Conference on Emerging Technologies & Factory Automation (ETFA 2012), 2012

We consider the problem of fixed priority scheduling of non-preemptive strict periodic tasks in c... more We consider the problem of fixed priority scheduling of non-preemptive strict periodic tasks in conjunction with sporadic preemptive tasks. There are few studies about the scheduling problem combining these two kinds of tasks. Moreover, only few results are available on scheduling non-preemptive strict periodic tasks since their performance analysis gives low success ratios, except in the case of harmonic tasks. Also, strict periodic tasks are of great importance since they are in charge for example of sensors/actuators or feedback control functions which are all critical in feedback control systems. Such tasks must have the highest priorities in order to guarantee a correct behavior of the control system. Preemptive sporadic tasks can be used for non critical functions and have lower priorities.

Proceedings of the 20th International Conference on Real-Time and Network Systems - RTNS '12, 2012

In this paper, we consider the problem of scheduling periodic Multi-Phase Multi-Thread tasks on a... more In this paper, we consider the problem of scheduling periodic Multi-Phase Multi-Thread tasks on a set of m identical processors with Earliest Deadline First (EDF) scheduling. Each periodic task is defined by a sequence of phases with offsets that can be possibly parallelized. We use a portioned semi-partitioned approach with migrations at local deadlines assigned to each phase. We extend this approach to take into account phase parallelism. The phase parallelism we consider is an extension of the popular job parallelism. A phase, if parallelizable, can be decomposed into parallel threads run on a configurable number of processors. We only require simultaneous execution of threads inside a window equal to the local deadline of their associated phase. To decide on the schedulability of a Multi-Phase Multi-Thread task, we extend the popular uniprocessor EDF feasibility condition for periodic asynchronous tasks. We propose two new schedulability tests for EDF that significantly improve the well known Leung and Merill feasibility test based on the feasibility interval [Omin, Omax + 2P ], where Omin and Omax are respectively the minimum and maximum phase offsets and P the least common multiple of the task periods. The first schedulability test is used when an EDF simulation is needed and gives, by simulation, a 44% gain in simulation speed. The second method provides a sufficient schedulability test with a time interval of length P based on the demand bound function. Finally, we study three local deadline assignment heuristics assigned to parallelizable phases. We compare and analyze the performances obtained by simulation for those three local deadline assignment heuristics.

Lecture Notes in Computer Science, 1998

Uniform reliable multicast protocols with a guaranteed response time are of concern in numerous d... more Uniform reliable multicast protocols with a guaranteed response time are of concern in numerous distributed real-time systems (e.g. distributed transactional systems, high available systems). We focus on uniform reliable multicast protocols in processors groups. The source of a message can belong or not to the destination group. A bounded number of processors crashes and network omissions is tolerated. The uniform

Applications for Flexibility and Agility, 2011

ABSTRACT In this chapter the authors focus on the problem of reconfiguring embedded real-time sys... more ABSTRACT In this chapter the authors focus on the problem of reconfiguring embedded real-time systems. Such reconfiguration can be decided either off-line to determine if a given application can be run on a different platform, while preserving the timeliness constraints imposed by the application, or on-line, where a reconfiguration should be done to adapt the system to the context of execution or to handle hardware or software faults. The task model considered in this chapter is the classical sporadic task model defined by a Worst Case Execution Time (WCET), a minimum inter-arrival time (also denoted the minimum Period) and a late termination deadline. The authors consider two preemptive scheduling strategies: Fixed Priority highest priority first (FP) and Earliest Deadline First (EDF). They propose a sensitivity analysis to handle reconfiguration issues. Sensitivity analysis aims at determining acceptable deviations from the specifications of a problem due to evolutions in system characteristics (reconfiguration or performance tuning). They present a state of the art for sensitivity analysis in the case of WCETs, Periods and Deadlines reconfigurations and study to what extent sensitivity analysis can be used to decide on the possibility of reconfiguring a system.

Scheduling theory, as it applies to hard-real-time environment, has been widely studied in the la... more Scheduling theory, as it applies to hard-real-time environment, has been widely studied in the last twenty years and it might be unclear to make it out within the plethora of results available. Our goal is first to collect in a single paper the results known for uniprocessor, non-idling, preemptive/non-preemptive, fixed/dynamic priority driven contexts, considering general task sets as a central figure for the description of possible processor loads. Second to establish new results when needed. In particular, optimality, feasibility conditions and worst-case response times are examined largely by utilizing the concepts of workload, processor demand and busy period. Some classic extensions such as jitter, resource sharing are also considered. Although this work is not oriented toward a formal comparison of these results, it appears that preemptive and non-preemptive scheduling are closely related and that the analysis of fixed versus dynamic scheduling might be unified according to the concept of higher priority busy period. In particular, we introduce the notion of deadline-d busy period for EDF schedules, that we conjecture to be an interesting parallel of the level-i busy period, a concept already used in the analysis of fixed priority driven scheduling.

We focus on the partitioned scheduling of sporadic real-time tasks with constrained deadlines. Th... more We focus on the partitioned scheduling of sporadic real-time tasks with constrained deadlines. The scheduling policy on each processor is staticpriority. The considered tasks are not independent and the consistency of these shared data is ensured by a multiprocessor synchronization protocol. Considering these assumptions, we propose a partitioned scheduling algorithm which tends to maximize the robustness of the tasks to the Worst Case Execution Time (WCET) overruns faults. We describe the context of the problem and we outline our solution based on simulated annealing.

ABSTRACT Real-time industrial domains are subject to strong constraints in terms of performance a... more ABSTRACT Real-time industrial domains are subject to strong constraints in terms of performance and reliability that directly increase the costs of their infrastructures. In order to build these infrastructures and to test them, we propose to implement ARTEMIS: Another Real-Time Engine for Message-Issued Sim- ulation. Its aim is to manage all real-time networks like CAN or AFDX and to simulate their behaviors in terms of scheduling and performance delay. To implement this tool, we use a modular way of development, building modules on a two-parts kernel. This architecture allows our software to be generic. Moreover, many interfaces can be easily integrated for several network implementations.

Our paper deals with a Dynamic Spectrum Access (DSA) and its implementation on a Software Defined... more Our paper deals with a Dynamic Spectrum Access (DSA) and its implementation on a Software Defined Radio (SDR) for IEEE 802.15.4e Networks. The network nodes select the carrier frequency after Energy-Detection based Spectrum Sensing (SS). To ensure frequency hoping between two nodes in IEEE 802.15.4e Network, we propose a synchronization algorithm. We considerate the IEEE 802.15.4e Network is Secondary User (SU), and all other networks are Primary Users (PUs) in unlicensed 868/915 MHz and 2450 MHz bands of a Cognitive Radio (CR). However, the algorithm and the energy-sensor have been implemented over GNU Radio and Universal Software Radio Peripheral (USRP) SDR. In addition, real packet transmissions have been performed in two cases. In the first case, SU communicates in static carrier-frequency, while in the second case with the implemented DSA. For each case, PU transmitter disturbs SU, which calculates Packet Success Rate (PSR) to measure the robustness of a used DSA. The obtained PSR is improved by 80\% when the SU accomplished DSA rather than a static access.

ABSTRACT In this paper, we focus on real-time switched Ether- net networks with mixed-criticality... more ABSTRACT In this paper, we focus on real-time switched Ether- net networks with mixed-criticality constraints. We are interested in (i) exploiting IEEE 1588 Precision Time Protocol (PTP) to implement criticality propagation techniques in such networks and (ii) analyzing delay of criticality switching. This work presents how to inte- grate criticality concepts for messages sent on Ethernet networks using PTP protocol. Concerning the delay of criticality switching, we consider FIFO and Fixed- Priority scheduling policies.

2015 IEEE 18th International Symposium on Real-Time Distributed Computing, 2015

Leveraging Applications of Formal Methods, 2007

Journal of Aerospace Computing, Information, and Communication, 2009

2007 IEEE Conference on Emerging Technologies & Factory Automation (EFTA 2007), 2007

In this paper, we propose to extend real-time feasibility conditions taking into account kernel o... more In this paper, we propose to extend real-time feasibility conditions taking into account kernel overheads for mixed preemptive periodic tasks with shared resources when tasks are scheduled with fixed priority FP/FIFO scheduling, where FIFO is used to arbitrate tasks having the same fixed priority. The kernel considered in this paper is an event driven OSEK kernel which uses the priority

Proceedings of the 8th international conference on New technologies in distributed systems - NOTERE '08, 2008

In this paper, we study the problem of maintaining the consistency of distributed objects in real... more In this paper, we study the problem of maintaining the consistency of distributed objects in real-time. Sporadic transactions sent by a set of clients must be processed by a set servers with a bounded end-to-end response time. We propose in this article a solution, following the state machine approach, based on a particular non-preemptive scheduling denoted EDF* (Earliest Deadline First

Proceedings of 2012 IEEE 17th International Conference on Emerging Technologies & Factory Automation (ETFA 2012), 2012

We consider the problem of fixed priority scheduling of non-preemptive strict periodic tasks in c... more We consider the problem of fixed priority scheduling of non-preemptive strict periodic tasks in conjunction with sporadic preemptive tasks. There are few studies about the scheduling problem combining these two kinds of tasks. Moreover, only few results are available on scheduling non-preemptive strict periodic tasks since their performance analysis gives low success ratios, except in the case of harmonic tasks. Also, strict periodic tasks are of great importance since they are in charge for example of sensors/actuators or feedback control functions which are all critical in feedback control systems. Such tasks must have the highest priorities in order to guarantee a correct behavior of the control system. Preemptive sporadic tasks can be used for non critical functions and have lower priorities.

Proceedings of the 20th International Conference on Real-Time and Network Systems - RTNS '12, 2012

In this paper, we consider the problem of scheduling periodic Multi-Phase Multi-Thread tasks on a... more In this paper, we consider the problem of scheduling periodic Multi-Phase Multi-Thread tasks on a set of m identical processors with Earliest Deadline First (EDF) scheduling. Each periodic task is defined by a sequence of phases with offsets that can be possibly parallelized. We use a portioned semi-partitioned approach with migrations at local deadlines assigned to each phase. We extend this approach to take into account phase parallelism. The phase parallelism we consider is an extension of the popular job parallelism. A phase, if parallelizable, can be decomposed into parallel threads run on a configurable number of processors. We only require simultaneous execution of threads inside a window equal to the local deadline of their associated phase. To decide on the schedulability of a Multi-Phase Multi-Thread task, we extend the popular uniprocessor EDF feasibility condition for periodic asynchronous tasks. We propose two new schedulability tests for EDF that significantly improve the well known Leung and Merill feasibility test based on the feasibility interval [Omin, Omax + 2P ], where Omin and Omax are respectively the minimum and maximum phase offsets and P the least common multiple of the task periods. The first schedulability test is used when an EDF simulation is needed and gives, by simulation, a 44% gain in simulation speed. The second method provides a sufficient schedulability test with a time interval of length P based on the demand bound function. Finally, we study three local deadline assignment heuristics assigned to parallelizable phases. We compare and analyze the performances obtained by simulation for those three local deadline assignment heuristics.

Lecture Notes in Computer Science, 1998

Uniform reliable multicast protocols with a guaranteed response time are of concern in numerous d... more Uniform reliable multicast protocols with a guaranteed response time are of concern in numerous distributed real-time systems (e.g. distributed transactional systems, high available systems). We focus on uniform reliable multicast protocols in processors groups. The source of a message can belong or not to the destination group. A bounded number of processors crashes and network omissions is tolerated. The uniform

Applications for Flexibility and Agility, 2011

ABSTRACT In this chapter the authors focus on the problem of reconfiguring embedded real-time sys... more ABSTRACT In this chapter the authors focus on the problem of reconfiguring embedded real-time systems. Such reconfiguration can be decided either off-line to determine if a given application can be run on a different platform, while preserving the timeliness constraints imposed by the application, or on-line, where a reconfiguration should be done to adapt the system to the context of execution or to handle hardware or software faults. The task model considered in this chapter is the classical sporadic task model defined by a Worst Case Execution Time (WCET), a minimum inter-arrival time (also denoted the minimum Period) and a late termination deadline. The authors consider two preemptive scheduling strategies: Fixed Priority highest priority first (FP) and Earliest Deadline First (EDF). They propose a sensitivity analysis to handle reconfiguration issues. Sensitivity analysis aims at determining acceptable deviations from the specifications of a problem due to evolutions in system characteristics (reconfiguration or performance tuning). They present a state of the art for sensitivity analysis in the case of WCETs, Periods and Deadlines reconfigurations and study to what extent sensitivity analysis can be used to decide on the possibility of reconfiguring a system.

In this paper we study the partitioning approach for multiprocessor real-time scheduling. This ap... more In this paper we study the partitioning approach for multiprocessor real-time scheduling. This approach seems to be the easiest since, once the partitioning of the task set has been done, the problem reduces to well understood uniprocessor issues. Meanwhile, there is no optimal and polynomial solution to partition tasks on processors. In this paper we analyze partitioning algorithms from several points of view such that for a given task set and specific constraints (processor number, task set type, etc.) we should be able to identify the best heuristic and the best schedulability test. We also analyze the influence of the heuristics on the performance of the uniprocessor tests and the impact of a specific task order on the schedulability. A study on performance difference between Fixed Priority schedulers and EDF in the case of partitioned scheduling is also considered.