Im Rahmen der Winteruniversität konnten sich heute einige studieninteressierte Schüler über das Informatikstudium informieren. Die dazu passenden Folien finden Sie hier: [Folien]

Oskar Pusz presents our paper Program-Structure–Guided Approximation of Large Fault Spaces at the 24th IEEE Pacific Rim International Symposium on Dependable Computing (PRDC '19) in Kyoto, Japan. In the paper we describe an approach to reduce the number of required fault injections using program-structure informations while aiming full fault-space coverage. Results show that injections can be reduced by up to 76 percent with an deviation of less than 2.7 percent and we keep the locality of the results regarding silent data corruptions to a low deviation.

Tobias Landsberg receives the award for best master thesis in the field of operating systems. The award is granted annually by the SIG on Operating Systems of the German Computer Assiciation (GI Fachgruppe Betriebssysteme) solely on the base of scientific excellence. It includes a price money of 500 €. Congrats, Tobias!

In his thesis Analyzing and Optimizing TLB-Induced Thread Migration Costs on Linux/ARM Tobias evaluates if it is feasable and benefitial to pre-warm the TLB (Translation Look-Aside Buffer) when a thread is migrated to another core. He analyzes existing ARM cores, presents and evaluates possible hardware extensions in gem5 and and provides a complete Linux integration for the system.

Linux Weekly News (LWN) features our recent work on analyzing kernel e-mail and the PaStA tool presented in our ICSE '19 and OpenSym '16 papers and recent talks by Ralf Ramsauer, Sebastian Duda, and Wolfgang Mauerer at ELCE '19 and LPC '19.

PaStA quantitatively analyses the evolution of patch stacks by mining git repositories, which is an important building block for analyzing patch-level optional features in the CADOS project.

Christian Dietrich successfully defends his PhD Thesis Interaction-Aware Analysis and Optimization of Real-Time Application and Operating System. Congrats, Christian!

Abstract: Mechanical and electronic automation was a key component of the technological advances in the last two hundred years. With the use of special-purpose machines, manual labor was replaced by mechanical motion, leaving workers with the operation of these machines, before also this task was conquered by embedded control systems. With the advances of general-purpose computing, the development of these control systems shifted more and more from a problem-specific one to a one-size-fits-all mentality as the trade-off between per-instance overheads and development costs was in favor of flexible and reusable implementations. However, with a scaling factor of thousands, if not millions, of deployed devices, overheads and inefficiencies accumulate; calling for a higher degree of specialization.

For the area of real-time operating systems, which form the base layer for many of these computerized control systems, we deploy way more flexibility than what is actually required for the applications that run on top of it. Since only the solution, but not the problem, became less specific to the control problem at hand, we have the chance to cut away inefficiencies, improve on system-analyses results, and optimize the resource consumption. However, such a tailoring will only be favorable if it can be performed without much developer interaction and in an automated fashion. Here, real-time systems are a good starting point, since we already have to have a large degree of static knowledge in order to guarantee their timeliness. Until now, this static nature is not exploited to its full extent and optimization potentials are left unused.

The requirements of a system, with regard to the RTOS, manifest in the interactions between the application and the kernel. Threads request resources from the RTOS, which in return determines and enforces a scheduling order that will ensure the timely completion of all necessary computations. Since the RTOS runs only in the exception, its reaction to requests from the application (or from the environment) is its defining feature.

In this thesis, I will grasp these interactions, and thereby the required RTOS semantic, in a control-flow--sensitive fashion. Extracted automatically, this knowledge about the reciprocal influence allows me to fit the implementation of a system closer to its actual requirements. The result is a system that is not only in its usage a special-purpose system, but also in its implementation and in its provided guarantees.

In the development of my approach, it became clear that the focus on these interactions is not only highly fruitful for the optimization of a system, but also for its end-to-end analysis. Therefore, this thesis does not only provide methods to reduce the kernel-execution overhead and a system's memory consumption, but it also includes methods to calculate tighter response-time bounds and to give guarantees about the correct behavior of the kernel. All these contributions are enabled by my proposed interaction-aware methodology that takes the whole system, RTOS and application, into account.

With this thesis, I show that a control-flow--sensitive whole-system view on the interactions is feasible and highly rewarding. With this approach, we can overcome many inefficiencies that arise from analyses that have an isolating focus on individual system components. Furthermore, the interaction-aware methods keep close to the actual implementation, and therefore are able to consider the behavioral patterns of the finally deployed real-time computing system.

Im Rahmen des Niedersachsen-Technikums hat uns eine Gruppe interessierter Abiturientinnen besucht. Während des 6-monatigem Programms lernen sie im Rahmen eines bezahlten Unternehmenspraktikums und eines Schnupper-Studiums das Arbeitsleben in einem MINT-Beruf kennen. Die jungen Frauen nahmen nach einem Vortrag an einem Kurzworkshop zum Programmieren teil, bei dem sie einen Unterschriftendrucker mithilfe des Kturtle-Programms in einer speziell dafür erstellten Programmiersprache programmieren konnten.

Florian Rommel presents our paper Wait-Free Code Patching of Multi-Threaded Processes at the 10th Workshop on Programming Languages and Operating Systems (PLOS '19) co-located with SOSP in Huntsville, Canada. The paper describes an approach to apply run-time code modification in multi-threaded processes without the need to stop all threads on a global barrier. This is achieved by first preparing a patched clone of the process’s address space and then migrating individual threads at predefined quiescence points while all other threads make uninterrupted progress.

Andreas Ziegler presents our paper Honey, I Shrunk the ELFs: Lightweight Binary Tailoring of Shared Libraries at the International Conference on Embedded Software (EMSOFT '19), in New York. In the paper we describe an approach to automatially reduce the footprint of existing shared libraries by removing unneeded functionality with lightweight binary tailoring. Our approach does not require access to the source code and effectively reduces the amount of code in all shared libraries on a Linux-based system by 63 percent and shrinks their files by 17 percent. The reduction in size is beneficial to cut down costs (e.g., lower storage and memory footprint) and eases code analyses that are necessary for code audits.

Lightweight application-specific tailoring of libraries is an important building block in our attempts towards a fully automatic whole-system tailoring of Linux-based infrastructure software in the CADOS project.

Romeo Shuka hat am seine Dissertation Parallele adaptive Schwarmsuche für Blackbox-Probleme erfolgreich verteidigt. Wir gratulieren!

Abstract: In der heutigen Wissenschaft und Wirtschaft haben wir es oft mit Systemen zu tun, welche aus Problemen bestehen, die sehr komplex und nicht einfach zu lösen sind. Aufgrund der zunehmenden Komplexität und der teilweise fehlenden Informationen ist es bereits heutzutage nicht mehr möglich, solche Probleme – welche als Blackbox-Probleme klassifiziert werden – per Hand zu lösen. Um das Maximum oder Minimum zu finden, wird auf Optimierungsmethoden zurückgegriffen, die uns ermöglichen, eine optimale Lösung für das Problem zu suchen und ggf. zu finden. Stochastische Methoden haben die letzten Jahre gezeigt, dass sie sehr gut geeignet sind, solche Probleme zu lösen. Der Vorteil der Verwendung von stochastischen Methoden ist, dass sie nicht den Gradienten des zu optimierenden Problems verwenden, so dass sie sowohl bei großen als auch bei komplexen Optimierungsproblemen erfolgreich angewendet werden können. Diese Vielseitigkeit hat aber ihren Preis. Es gibt hauptsächlich drei wesentliche Aspekte, die die Effizienz der Lösung beeinträchtigen:

1. Die realen Probleme werden immer größer und komplizierter oder sie müssen in sehr kurzer Zeit gelöst werden, was erhebliche Ressourcen in Zeit und Hardware erfordert.
2. Optimierungsprobleme sind durch mehrere lokale Optima charakterisiert, die ein Verfahren zur Vermeidung einer zu frühen Konvergenz erfordern.
3. Algorithmen erfordern einige problembedingte Anpassungen ihrer Verhaltensparameter, um bessere Ergebnisse zu erzielen.

In dieser Arbeit wird ein Framework (Parallel Adaptive Swarm Search - PASS) vorgestellt, das die Ermittlung der möglichst optimalen Lösung für Black-box Probleme gewährleistet. Durch das Framework kann der Nutzer eine Mapping des Algorithmus an die vorhandene Hardware und Software (Problemart) realisieren. Es werden alle drei oben genannten Probleme behandelt. Das Problem der Parallelisierung wird durch die Umwandlung des Algorithmus von seriell zu parallel gelöst. Das Problem des Stillstands wird durch das Benutzen des Island Models behandelt und für das Problem der Adaptivität wird ein neuer Suchalgorithmus vorgestellt, welcher die Suche der optimalen Parameter beschleunigt. In dieser Arbeit wird PASS mit bekannten Verfahren aus der Literatur (wie z.B. Particle Swarm Optimization, Differential Evolution, Artificial Bee Colony usw.) mit unterschiedlichen Benchmark-Problemen verglichen. Die erste Gruppe der Benchmark-Probleme besteht aus synthetischen Funktionen bekannt aus der Literatur (wie z.B. Rastrigin Funktion, Rosenbrock Funktion) und die zweite Gruppe besteht aus Problemen aus der realen Welt.
Untersuchungen in dieser Arbeit haben gezeigt, dass die Anpassungen zu besse ren Ergebnissen führen. Durch die adaptive Natur des Frameworks, ist es in vielen Rechnerarchitekturen nutzbar und für viele Probleme anwendbar.

Gerion Entrup presents our paper ARA: Automatic Instance-Level Analysis in Real-Time Systems at the 15th Workshop on Operating System Platforms for Embedded Real-Time Applications (OSPERT '19), in Stuttgart. In the paper we describe ARA, an analysis framework and tool to detect and visualize, how a given application employs RTOS abstractions. As a tool, ARA helps to understand how the tasks of an application given as source code interact which each other. The framework itself is an important building block towards our goal of fully automatic application analysis in the AHA project.

Im Rahmen der SommerUni (ehem. Herbstuniversität) ist ein Angebot speziell für Mädchen der 10. bis 13. Klassen, die sich für ein Studium im Bereich Mathematik, Informatik, Naturwissenschaften oder Technik (MINT) interessieren. Am SRA erhielten die Teilnehmerinnen Einblicke in das Informatikstudium und das grundlegende Konzept von CPU Scheduling. Die dazu passenden Folien finden Sie hier: [Folien]

Ralf Ramsauer presents the paper The List is the Process: Reliable Pre-Integration Tracking of Commits on Mailing Lists at the 41^st International Conference on Software Engineering 2019 in Montreal. In the paper we present an approach and tooling to track otherwise invisible evolution of software changes discussed on mailing lists by connecting all early revisions of changes to their final version in the repository. Since artefact modifications on mailing lists are communicated by updates to fragments (i.e., patches) only and furthermore integrated and changed by maintainers before becoming visible in the repository, identifying semantically similar changes is a nontrivial task that our approach solves in a language-independent way. This can be used for assessing properties of open-source software (OSS) development processes, which is an essential requirement for using OSS, such as the Linux kernel, in reliable or safety-critical industrial products (e.g., autonomous driving), where certifiability and conformance to processes are crucial.

Florian Rommel presents the paper Multiverse: Compiler-Assisted Management of Dynamic Variability in Low-Level System Software at the Fourteenth EuroSys Conference 2019 in Dresden. In the paper we address run-time patching of binary code depending on some configuration variables. Based on seldom changing variables, the call-sites of certain functions are changed to ones pointing to specialized functions, for example ones without run-time checks of the configuration values. This allows specializing code at run-time, i.e. having dynamic variability. At load-time the code has all features and with our approach can be specialized at any time to any state, making run-time checks unnecessary.

Tobias Landsberg joins the SRA team as Doctoral Researcher. He will strengthen our research team and, in the upcoming semester, he will manage our Bachelor's seminar (Proseminar Parallelverarbeitung) and assist in our Master's project (Projekt SRA). Welcome, Tobias!

Der Student Malte Bargholz wurde im Rahmen des Tags der Fakultät für seine herausragenden Leistungen in seiner Bachelorprüfung geehrt. Seine herausragenden Leistungen stellte er, unter anderem, in seiner Bachelorarbeit InterSloth: Globales Hardware-gesteuertes Scheduling in einem Multikern-Echtzeitbetriebssystem auf RISC-V beim SRA unter Beweis und konnte seine Ergebnisse beim Herbsttreffen der Fachgruppe Betriebssysteme vorstellen.

Im Rahmen des Niedersachsen-Technikums hat uns eine Gruppe interessierter Frauen besucht. Während des 6-monatigem Programms lernen sie im Rahmen eines bezahlten Unternehmenspraktikums und eines Schnupper-Studiums das Arbeitsleben in einem MINT-Beruf kennen. [Folien]

Christian Dietrich presents the paper Semi-Extended Tasks: Efficient Stack Sharing Among Blocking Threads at the IEEE Real-Time Systems Symposium in Nashville, TE, USA (RTSS `18). In the paper we adress the problem of worst-case stack consumption (WCSC) in real-time systems that support preemption and blocking of threads. We refine the stack-sharing granularity from the thread to function level and provide an efficient intra-thread stack-switch mechanism as well as an ILP-based analysis approach to realize tight WCSC boundaries.

Prof. Dr.-Ing. habil. Daniel Lohmann gave his inaugural lecture at the Faculty of Electrical Engineering and Computer Science. In his presentation "Klein und sicher – Automatisch anpassbare Systemsoftware für eingebettete Spezialzweckanwendungen", Prof. Lohmann provided an entertaining introduction into our research activities and the case for highly tailorable system software.

Studenten und Mitarbeiter des SRA nehmen am Herbstreffen der Fachgruppe Betriebssysteme in Coburg teil. Das SRA ist mit zwei Vorträgen vertreten. Malte Bargholz spricht über „InterSloth: Hardwaregestützte, globale und prioritätsgesteuerte Echtzeiteinplanung“ und Christian Dietrich präsentiert seine Arbeit über „Semi-Extended Tasks: Geteilter Stack für selbstblockierende Fäden“.

Stefan Naumann joins the SRA team as Doctoral Researcher. He will strengthen our research team and, in this semester, he will manage our Master's seminar on Coprocessors and their Management in Operating Systems. Welcome, Stefan!

Björn Fiedler presents our paper Levels of Specialization in Real-Time Operating Systems was at the 14th Workshop on Operating System Platforms for Embedded Real-Time Applications (OSPERT '18), in Barcelona. In the paper we describe a taxonomy for the specialization of system software towards a specific application and provide showcases of the achievable benefits. We got an Best Paper Award for this work.

Wolfgang Schröder-Preikschat is visiting our group and will present his work in the computer science colloquium.

Predictability Issues in Operating Systems, 15:00, L3S multimedia room, Appelstr. 9, 15th floor

Predictability is always subject to the underlying assumptions being made. For real-time systems, time response of processes in relation to the strictness of deadlines is of particular importance. With an additional focus on embedded systems, space and energy requirements become relevant as well and need to be considered in combination. As far as software is concerned, structure and organisation of the programs to be executed determines whether or not predictable processes will take place in a given computing system. Design for predictability is an overarching aspect that crosscuts the whole computing system and particularly addresses operating systems.

This talk is about structuring principles of non-sequential programs - in the shape of but not limited to operating systems - to abet predetermination of quality attributes of non-sequential (real-time) processes, it is not about analytical methods to effectively predetermine these attributes. Issues in operating systems as to space, timing, and energy requirement are touched. Emphasis thereby is on coordination of cooperation and competition between processes, namely synchronisation. It is shown how measures of process synchronisation against the background of many-core processors cater to these issues.

Our paper Cross-Layer Fault-Space Pruning for Hardware-Assisted Fault Injection is presented by Christian Dietrich at the 55th Design Automation Conference in San Francisco. The paper describes a method to calculate fault-masking terms that are used to prune the fault space of a flip-flop level fault injection dynamically. Thereby, we can shrink the fault space by up to 20 percent.

Nach einer langen und erfolgreichen akademischen Karriere verabschiedet sich der bisherige Leiter des Fachgebietes System- und Rechnerarchitektur, Herr Prof. Dr.-Ing. Christian Müller-Schloer, zum 1. April 2018 in den wohlverdienten Ruhestand. Nach Studium und Promotion an der Technischen Universität München arbeitete Prof. Müller-Schloer bei den Siemens Corporate Research Labartories. Im Jahr 1991 erhielt er den Ruf an die Leibniz Universität Hannover und gründete den heutigen Fachbereich System- und Rechnerarchitektur, der zunächst unter dem Namen "Institut für Rechnerstrukturen und Betriebssysteme" firmierte und die Entstehung und Entwicklung der Informatik an der Leibniz Universität Hannover maßgeblich prägte. Neben seinem hohen Einsatz für die Informatik in Hannover über viele Jahre hinweg, begründete und prägte Prof. Christian Müller-Schloer das Forschungsgebiet des Organic Computing. Der Fachbereich System- und Rechnerarchitektur verabschiedet sich von seinem langjährigen Leiter und bedankt sich für viele Jahre interessanter Diskussionen, gemeinsam errungenener Erkenntnisse und schöner Erlebnisse.

Systemsoftware für die Industrie von morgen und das Internet der Dinge

Mit Unterstützung der Kollegen vom IKT findet das erste Gesamttreffen des neu gegründeten Fachbereich SYS der Gesellschaft für Informatik (GI) am 1. und 2. März 2018 hier in Hannover statt. Mit mehr als zwölf Beiträgen aus dem Bereich der Betriebssysteme, Kommunikationssysteme und Verteilten Systeme erwartet die 70 angmeldeten Teilnehmer ein spannendes Programm.

Die als Meltdown und Spectre bekannt gewordenen Angriffe verunsichern zur Zeit Anwender und Experten. Prof. Daniel Lohmann hat heute im Rahmen einer Informationsveranstaltung des LUIS für Systemadministratoren der Universität die technischen Grundlagen aus Rechnerarchitektur und Betriebssystemen am Beispiel von Meltdown präsentiert. Die Folien des Vortrags finden Sie hier: [Folien]

Organisiert durch den Fachrat Informatik gab es heute eine kleine Informationsveranstaltung für Erstsemester über Forschung und Lehre am SRA und die Bedeutung der systemnahen Informatik. Die dazu passenden Folien finden Sie hier: [Folien]

Im Rahmen einer Informationsveranstaltung an der Evangelischen Akademie Loccum wurde einer Gruppe von Schülern die Inhalte und Herausforderungen des Informatikstudiums näher gebracht. Die dazu passenden Folien finden Sie hier: [Folien]

With Björn Fiedler and Florian Rommel two new Doctoral Researchers join the SRA team to strenghten our research team in the AHA and CADOS DFG projects. On the teaching side, they will help us to develop new projects and courses in the systems domain. Welcome, Björn! Welcome, Florian!

Im Rahmen des Niedersachsen-Technikums hat uns eine Gruppe interessierter Frauen besucht. Während des 6-monatigem Programms lernen sie im Rahmen eines bezahlten Unternehmenspraktikum und eines Schnupper-Studium das Arbeitsleben in einem MINT-Beruf kennen. [Folien]

AHA: Automated Hardware Abstraction in Operating-System Engineering (DFG: LO 1719/4-1)

Goal of AHA is to improve nonfunctional properties of system software by a very deep, but fully automated specialization of the application-hardware bridge represented by the operating system. We investigate, how alternative implementations that are mapped more directly to hardware features, can be generated from a concrete application and their actual interactions with the operating system.

The German research foundation DFG is now supporting our AHA project for three years with two positions for doctoral researchers (E13), two positions for student researchers, and some additional lab equippment.

Christian Dietrich presents the paper Automatic Verification of Application-Tailored OSEK Kernels at the ACM / IEEE Conference on Formal Methods in Computer-Aided Design in Vienna. In the paper, which is joint work with the Theoretical Computer Science group of Lutz Schröder and Stefan Milius (FAU), we describe a new approach to verify an RTOS kernel not against its abstract specification, but only the semantics actually used by the concrete application.

Gerion Entrup joins the SRA team as Doctoral Researcher. He will manage our new Master's seminar on Linux Kernel Architecture and strenghten our research team in the field of static analysis and code generation for the AHA project. Welcome, Gerion!

Christian Dietrich presents our paper cHash: Detection of Redundant Compilations via AST Hashing at the USENIX ATC 2017 conference. In the paper we describe a new approach to quickly decide which files really need to be recompiled after some change to the source code. We got an Best Paper Award for this work.

Christian Dietrich presents the paper OSEK-V: Application-Specific RTOS Instantiation in Hardware at the ACM SIGPLAN / SIGBED Conference on Languages, Compilers, and Tools for Embedded Systems in Barcelona. In the paper we describe our approach to automatically tailor the RTOS functionality needed by an OSEK application to integrate it directly into the processor pipeline of the Rocket RISC-V core.

Christian Dietrich presented the paper SysWCET: Whole-System Response-Time Analysis for Fixed-Priority Real-Time Systems at the 2017 IEEE Real-Time and Embedded Technology and Applications Symposium in Pittsburgh. We got an Outstanding Paper Award for this work.

Our new student laboratory has been established. Equipped with 11 high-end PC workstations, we now have an excellent environment for our students working on their BA/MA thesis as well as new hands-on lectures and laboratories in systems.

Our paper Global Optimization of Fixed-Priority Real-Time Systems by RTOS-Aware Control-Flow Analysis finally appeared in issue 16.2 of ACM Transactions on Embedded Computing Systems. The paper is an extended version of our LCTES '15 paper Cross-Kernel Control-Flow-Graph Analysis for Event-Driven Real-Time Systems, where we originally described our approach to exploit the deterministic scheduling of OSEK and other event-driven RTOS to establish a global, cross-kernel/inter-task control flow analysis for aggressive tailoring and optimization. This journal version extends the original article by an algorithmic alternative that trades efficiency for precision and broader case studies.

Daniel Lohmann investigates together with his doctoral researchers Christian Dietrich und Oskar Pusz principles, methods and techniques for the development of highly adaptable systems software targeted as special-purpose systems. His teaching activities will focus on the topic of operating systems and the broader area of systems software development in general.

Daniel Lohmann wird von Staatsminister Dr. Ludwig Spaenle „in Würdigung seiner Vorbildfunktion mit dem Preis für gute Lehre 2015 des Freistaats Bayern“ ausgezeichnet. Der mit 5000 EUR dotierte Preis wird jährlich an 15 herausragende Wissenschaftlerinnen und Wissenschaftler vergeben.

Die Kriterien für die Auszeichnung sind eine herausragende Lehrleistung über die Dauer von wenigstens zwei Studienjahren an einer Universität in Bayern, eine Beteiligung der Studierenden an der Auswahl sowie der Vorschlag der jeweiligen Universität. Über alle Maßnahmen zur Sicherung der Qualität der Lehre, die von den Hochschulen praktiziert werden, spielen das persönliche Engagement und die pädagogisch-didaktischen Kompetenzen des Lehrenden eine große Rolle.

CADOS research students gave two talks at LPC '14: Valentin Rothberg talked about his new tool undertaker-checkpatch, which analyzes patch files. The vampyr tool to configurability-aware compile test (or determine the variability of) source files was presented by Stefan Hengelein.

Linux Weekly News features both CADOS talks and tools in its summary of the LPC highlights!