Predictable composition of memory accesses on many-core processors

International audienceThe use of many-core COTS processors in safety critical embedded systems is a challenging research topic. The predictable execution of several applications on those processors is not possible without a precise analysis and mitigation of the possible sources of interference. In this paper, we identify the external DDR-SDRAM and the Network on Chip to be the main bottlenecks for both average performance and predictability in such platforms. As DDR-SDRAM memories are intrinsically stateful, the naive calculation of the Worst-Case Execution Times (WCETs) of tasks involves a significantly pessimistic upper-bounding of the memory access latencies. Moreover, the worst-case end-to-end delays of wormhole switched networks cannot be bounded without strong assumptions on the system model because of the possibility of deadlock. We provide an analysis of each potential source of interference and we give recommendations in order to build viable execution models enabling efficient composable computation of worst-case end-to-end memory access latencies compared to the naive worst-case-everywhere approach

Predictable execution on many-core processors

Dans cette thèse, nous étudions l’adéquation de l’architecture distribuée des processeurs pluricoeurs avec les besoins des concepteurs de systèmes temps réels avioniques. Nous proposons d’abord une analyse détaillée d’un processeur sur étagère (COTS), le KALRAY MPPA®-256, et nous identifions certaines de ses ressources partagées comme étant les goulots d’étranglement limitant à la fois la performance et la prédictibilité lorsque plusieurs applications s’exécutent. Pour limiter l’impact de ces ressources sur les WCETs, nous définissons formellement un modèle d’exécution isolant temporellement les applications concurrentes. Son implantation est réalisée au sein d’un hyperviseur offrant à chaque application un environnement d’exécution isolé et assurant le respect des comportements attendus en ligne. Sur cette base, nous formalisons la notion de partition comme l’association d’une application avec un budget de ressources matérielles. Dans notre approche, les applications s’exécutant au sein d’une partition sont garanties d’être temporellement isolées des autres applications. Ainsi, étant donné une application et son budget associé, nous proposons d’utiliser la programmation par contraintes pour vérifier automatiquement si les ressources allouées à l’application sont suffisantes pour permettre son exécution de manière satisfaisante. Dans le même temps, dans le cas où un budget est effectivement valide, notre approche fournit un ordonnancement et un placement complet de l’application sur le sous-ensemble des ressources du processeurallouées à sa partition.In this thesis, we study the suitability of the distributed architecture of many-core processors for the design of highly constrained real-time systems as is the case in avionics. We firstly propose a thorough analysis of an existing COTS processor, namely the KALRAY MPPA®-256, and we identify some of its shared resources to be paths of interference when shared among several applications. We provide an execution model to restrict the access to these resources in order to mitigate their impact on WCETs and to temporally isolate co-running applications. We describe in detail how such an execution model can be implemented with a hypervisor which practically provides the expected property of temporal isolation at run-time. Based on this, we formalize a notion of partition which represents the association of an application with a resource budget. In our approach, an application placed in a partition is guaranteed to be temporally isolated from applications placed in other partitions. Then, assuming that applications and resource budgets are given,we propose to use constraint programming in order to verify automatically whether the amount of resources requested by a budget is sufficient to meet all of the application’s constraints. Simultaneously, when a budget is valid, our approach computes a schedule of the application on the subset of the processor’s resources allocated to it

Exécution prédictible sur processeurs pluri-cœurs

During the last 25 years, the need for computational power aboard aircrafts has been constantly growing. To support these evolutions, aircraft manufacturers need to bring massive computational power aboard in order to host more and more applications of increasing size.The emergence of promising technologies such as many-core processors thus appears as a good opportunity to tackle this challenge. Yet they also raise issues regarding predictable execution of software. In this context, we provide an end-to-end integration framework enabling to share and to leverage the parallel computational power of many-core processors safely. By doing so, we pave the way for the design of future embedded avionics computers based on many-core processors. More precisely, we propose a thorough analysis of an existing COTS processor, namely the Kalray MPPA-256, and we identify some of its hared resources to be paths of interference when shared among several applications. We provide an execution model to restrict the access to these resources in order to mitigate their impact on software execution times. We describe in detail how such an execution model can be implemented with a hypervisor which practically provides the expected property of temporal isolation at run-time. Based on this, we formalize a notion of partition which represents the association of an application with a resource budget. Since we aim to execute applications of industrial size, we automatically schedule them on their partitions' resources using Constraint Programming.Les besoins en puissance de calcul à bord des avions augmentent régulièrement depuis 25 ans. Pour accompagner ces évolutions, les avionneurs doivent concevoir des calculateurs toujours plus puissants devant héberger des applications toujours plus massives et nombreuses.L'émergence de technologies prometteuses telles que les processeurs pluri-cœurs semble ainsi être une bonne opportunité pour répondre à ces attentes mais présente également de nouveaux défis pour l'exécution prédictible de logiciel. Dans ce contexte, nous proposons un atelier d'intégration de bout en bout qui permet le partage et l'exploitation de la puissance de calcul parallèle d'une cible pluri-cœurs avec des applications contraintes, réalisant ainsi un premier pas vers la conception de calculateurs avioniques à base de processeurs pluri-cœurs. Plus précisément, nous proposons une analyse détaillée d'un processeur sur étagère, le Kalray MPPA-256, et identifions certaines de ses ressources partagées comme étant lespoints de contention réduisant la prédictibilité lors d'exécutions parallèles. Pour résoudre ce problème, nous définissons formellement un modèle d'exécution isolant temporellement les applications concurrentes. Son implantation est réalisée au sein d’un hyperviseur qui garantit le respect des comportements attendus en-ligne. Nous formalisons une notion de partition comme l'association d'une application avec un budget de ressources matérielles. Considérant des applications industrielles de grande taille, nous calculons automatiquement l'ordonnancement et le placement d'une application sur les ressources de sa partition en utilisant la programmation par contraintes

Examining word writing in handwriting and smartphone-writing: orthographic processing affects movement production in different ways

International audienceNew technological devices are changing the way we communicate. With the popularization of smartphones, some people spend more time writing on a phone than handwriting or typing on a keyboard. Does phone-writing change the way we process orthographic information? Does this affect movement production? In the present study, French participants had to write words in a spelling to dictation task. They wrote orthographically consistent and inconsistent short and long words. First, they had to write the words by hand in upper-case letters on a digitizer. One month later, they had to write the words on a smartphone. The results revealed that orthographic consistency affects the spelling processes in both handwriting and phone-writing. We observe more spelling errors for inconsistent words than consistent ones. When analyzing the movement production of the words that were spelled correctly, the data revealed that the timing of orthographic processing differs between the two ways of writing. Orthographic consistency seems to affect the time before movement initiation (latency data) in handwriting, especially in short words. In addition, once the participant starts to write, it also mediates movement production throughout the whole word, affecting the timing of the initial and final letters of the word. In phone-writing, orthographic consistency tends to modulate movement production at the end of the word. Inconsistent words require more processing time than consistent words, especially when they are long. These timing differences are not surprising, since the whole word writing process is much longer in handwriting than in phone-writing. We are preparing another phone-writing experiment in which we examine the implementation of word suggestions. With word suggestions, the spelling processes are no longer a mere recall of information on the letter components of a word. While writing the first letters, smartphones suggest words on top of the virtual keyboard to complete the target word before we write the last letters. This back and forth mechanism of writing letters, reading word suggestions and selecting one of them, radically changes the way we process orthographic information during word writing

Writing words by hand and by phone: Differences in the timing of orthographic processing

International audienceTexting and email writing with smartphones are activities that are done regularly by a very importantproportion of the population. Phonewriting (PW) differs from handwriting (HW) in many ways.Previous HW research revealed that the orthographic processes modulate movement production(see APOMI, Kandel, 2023). Do spelling processes also affect hand movements in PW? To answer thisquestion, we focused on orthographic processing in HW and PW in a spelling-to-dictation task inFrench. We manipulated orthographic consistency and length. First, the participant had to write thewords by hand in upper-case letters on a digitizer. One month later, they had to write the words on asmartphone. We collected data on latency, letter movement duration, errors and online corrections.The data revealed that the timing of orthographic processing differs between handwriting andphonewriting. Latencies -i.e., the time before starting to write- were longer in PW than HW. Incontrast, once we start writing the word, the hand movements took longer in HW than PW. AlthoughPW takes less writing time, errors and online corrections are far more frequent than in HW. Latenciesfor orthographically inconsistent words were longer than for consistent words, both in HW and PW.However, the mean letter duration of orthographically inconsistent words was longer than forconsistent words only in HW but not for PW. Also, inconsistent words elicited a higher number ofphonologically plausible errors than consistent words, in HW and PW.The impact of the technological progress due to the telephone is to decrease the time we spendwriting but the cognitive cost is that we produce more errors and online corrections. Regardingorthographic processing, HW and PW are very different. In PW most of the central processing is donebefore starting to write. In HW, spelling processes start before movement initiation but are stillactive while we write. This modulates movement production

Examining word writing in handwriting and smartphone-writing: orthographic processing affects movement production in different ways

International audienceNew technological devices are changing the way we communicate. With the popularization of smartphones, some people spend more time writing on a phone than handwriting or typing on a keyboard. Does phone-writing change the way we process orthographic information? Does this affect movement production? In the present study, French participants had to write words in a spelling to dictation task. They wrote orthographically consistent and inconsistent short and long words. First, they had to write the words by hand in upper-case letters on a digitizer. One month later, they had to write the words on a smartphone. The results revealed that orthographic consistency affects the spelling processes in both handwriting and phone-writing. We observe more spelling errors for inconsistent words than consistent ones. When analyzing the movement production of the words that were spelled correctly, the data revealed that the timing of orthographic processing differs between the two ways of writing. Orthographic consistency seems to affect the time before movement initiation (latency data) in handwriting, especially in short words. In addition, once the participant starts to write, it also mediates movement production throughout the whole word, affecting the timing of the initial and final letters of the word. In phone-writing, orthographic consistency tends to modulate movement production at the end of the word. Inconsistent words require more processing time than consistent words, especially when they are long. These timing differences are not surprising, since the whole word writing process is much longer in handwriting than in phone-writing. We are preparing another phone-writing experiment in which we examine the implementation of word suggestions. With word suggestions, the spelling processes are no longer a mere recall of information on the letter components of a word. While writing the first letters, smartphones suggest words on top of the virtual keyboard to complete the target word before we write the last letters. This back and forth mechanism of writing letters, reading word suggestions and selecting one of them, radically changes the way we process orthographic information during word writing

Writing words by hand and by phone: Differences in the timing of orthographic processing

International audienceTexting and email writing with smartphones are activities that are done regularly by a very importantproportion of the population. Phonewriting (PW) differs from handwriting (HW) in many ways.Previous HW research revealed that the orthographic processes modulate movement production(see APOMI, Kandel, 2023). Do spelling processes also affect hand movements in PW? To answer thisquestion, we focused on orthographic processing in HW and PW in a spelling-to-dictation task inFrench. We manipulated orthographic consistency and length. First, the participant had to write thewords by hand in upper-case letters on a digitizer. One month later, they had to write the words on asmartphone. We collected data on latency, letter movement duration, errors and online corrections.The data revealed that the timing of orthographic processing differs between handwriting andphonewriting. Latencies -i.e., the time before starting to write- were longer in PW than HW. Incontrast, once we start writing the word, the hand movements took longer in HW than PW. AlthoughPW takes less writing time, errors and online corrections are far more frequent than in HW. Latenciesfor orthographically inconsistent words were longer than for consistent words, both in HW and PW.However, the mean letter duration of orthographically inconsistent words was longer than forconsistent words only in HW but not for PW. Also, inconsistent words elicited a higher number ofphonologically plausible errors than consistent words, in HW and PW.The impact of the technological progress due to the telephone is to decrease the time we spendwriting but the cognitive cost is that we produce more errors and online corrections. Regardingorthographic processing, HW and PW are very different. In PW most of the central processing is donebefore starting to write. In HW, spelling processes start before movement initiation but are stillactive while we write. This modulates movement production

Computational trust and reputation models for open multi-agent systems: a review

In open environments, agents depend on reputation and trust mechanisms to evaluate the behavior of potential partners. The scientific research in this field has considerably increased, and in fact, reputation and trust mechanisms have been already considered a key elements in the design of multi-agent systems. In this paper we provide a survey that, far from being exhaustive, intends to show the most representative models that currently exist in the literature. For this enterprise we consider several dimensions of analysis that appeared in three existing surveys, and provide new dimensions that can be complementary to the existing ones and that have not been treated directly. Moreover, besides showing the original classification that each one of the surveys provide, we also classify models that where not taken into account by the original surveys. The paper illustrates the proliferation in the past few years of models that follow a more cognitive approach, in which trust and reputation representation as mental attitudes is as important as the final values of trust and reputation. Furthermore, we provide an objective definition of trust, based on Castelfranchi's idea that trust implies a decision to rely on someone. © 2011 Springer Science+Business Media B.V.This work was supported by the EC by the project LiquidPub (STREP FP7-213360), by the Spanish Education and Science Ministry with the projects AEI (TIN2006-15662-C02-01), AT (CONSOLIDER CSD2007-0022, INGENIO 2010) and RepBDI (Intramural 200850I136), and by the Generalitat de Catalunya under the grants 2009-SGR-1433 and 2009-SGR-1434.Peer Reviewe