AQuoSA - adaptive quality of service architecture

This paper presents an architecture for quality of service (QoS) control of time-sensitive applications in multi-programmed embedded systems. In such systems, tasks must receive appropriate timeliness guarantees from the operating system independently from one another; otherwise, the QoS experienced by the users may decrease. Moreover, fluctuations in time of the workloads make a static partitioning of the central processing unit (CPU) that is neither appropriate nor convenient, whereas an adaptive allocation based on an on-line monitoring of the application behaviour leads to an optimum design. By combining a resource reservation scheduler and a feedback-based mechanism, we allow applications to meet their QoS requirements with the minimum possible impact on CPU occupation. We implemented the framework in AQuoSA (Adaptive Quality of Service Architecture (AQuoSA). http://aquosa.sourceforge.net), a software architecture that runs on top of the Linux kernel. We provide extensive experimental validation of our results and offer an evaluation of the introduced overhead, which is perfectly sustainable in the class of addressed applications

CloudNetSim - Simulation of Real-Time Cloud Computing Applications

In this paper, we describe CloudNetSim, a project aiming to realise a simulation platform supporting our ongoing and planned research activities in the area of resource management and scheduling for distributed QoS-sensitive and soft real-time applications. It is based on OMNeT++, integrating in the platform a set of modules for the simulation of CPU scheduling, including hierarchical scheduling at both levels of the hypervisor and guest Operating System, as needed when simulating cloud infrastructures. Thanks to the modularity of OMNeT++, CloudNetSim may easily leverage many existing simulation models already available for networking, including standard network components and protocols, such as TCP/IP. After a brief overview of related simulation tools found in the literature, and the discussion of their limitations, we provide a detailed description of the internals of our simulator. Then, we show results gathered from a few representative scenarios demonstrating how its behaviour matches with the one of simple real applications

Handling timing constraints violations in soft real-time applications as exceptions

In this paper, an exception-based programming paradigm is envisioned to deal with timing constraints violations occurring in soft real-time and multimedia applications written in the C language. In order to prove viability of the approach, a mechanism allowing to use such paradigm has been designed and implemented as an open-source library of C macros making use of the standard POSIX API (a few Linux-specific optimizations are also briefly discussed). The proposed approach has been validated by modifying mplayer, one of the most widely used multimedia player for Linux, so as to use the introduced library. An extensive experimental evaluation has been made, both when running the player alone and when mixing it with a workload of other synthetic real-time applications. In the latter case, different scheduling policies have been used, including both standard priority-based ones as available on the mainline Linux, and an experimental deadline-based one available as a separate patch. The shown results demonstrate how the exception-based paradigm is effective in improving the audio/video delay exhibited by the player achieving a superior performance and a dramatically better quality of experience as compared to the original heuristic frame-dropping mechanism of the player

EDF scheduling of real-time tasks on multiple cores: Adaptive Partitioning vs. Global Scheduling

This paper presents a novel migration algorithm for real-time tasks on multicore systems, based on the idea of migrating tasks only when strictly needed to respect their temporal constraints and a combination of this new algorithm with EDF scheduling. This new “adaptive migration” algorithm is evaluated through an extensive set of simulations showing good performance when compared with global or partitioned EDF: our results highlight that it provides a worst-case utilisation bound similar to partitioned EDF for hard real-time tasks and an empirical tardiness bound (like global EDF) for soft real-time tasks. Therefore, the proposed scheduler is effective for dealing with both hard and soft real-time workloads

Message from the General Chairs

REACTION 2013. 2nd International Workshop on Real-time and distributed computing in emerging applications. December 3rd, 2013, Vancouver, Canada

Analysis and implementation of the multiprocessor bandwidth inheritance protocol

The Multiprocessor Bandwidth Inheritance (M-BWI) protocol is an extension of the Bandwidth Inheritance (BWI) protocol for symmetric multiprocessor systems. Similar to Priority Inheritance, M-BWI lets a task that has locked a resource execute in the resource reservations of the blocked tasks, thus reducing their blocking time. The protocol is particularly suitable for open systems where different kinds of tasks dynamically arrive and leave, because it guarantees temporal isolation among independent subsets of tasks without requiring any information on their temporal parameters. Additionally, if the temporal parameters of the interacting tasks are known, it is possible to compute an upper bound to the interference suffered by a task due to other interacting tasks. Thus, it is possible to provide timing guarantees for a subset of interacting hard real-time tasks. Finally, the M-BWI protocol is neutral to the underlying scheduling policy: it can be implemented in global, clustered and semi-partitioned scheduling. After introducing the M-BWI protocol, in this paper we formally prove its isolation properties, and propose an algorithm to compute an upper bound to the interference suffered by a task. Then, we describe our implementation of the protocol for the LITMUS RT real-time testbed, and measure its overhead. Finally, we compare M-BWI against FMLP and OMLP, two other protocols for resource sharing in multiprocessor systems

Adopting Redundancy Techniques for Multicast Stream Authentication

Various schemes have been proposed to achieve strong authentication of streamed data in a lossy network by means of "light" digital signatures. Such techniques perform a strong authentication on only one packet, to which others are linked by means of hash functions, so that the authentication property propagates to them too. Most of these schemes make the basic assumption that the signature packet is not lost, even if no practical and precise solutions are proposed that guarantee such a property. In this paper we show how adoption of some redundancy techniques can be used in the context of multicast stream authentication in order to increase probability that the signature packets are received and correctly verified against their digital signature. Finally some experimental results are presented comparing computational overheads due to the authentication schemes both at the sender and at the receiver

Confidential execution of cloud services

In this paper, we present Confidential Domain of Execution (CDE), a mechanism for achieving confidential execution of software in an otherwise untrusted environment, e.g., at a Cloud Service Provider. This is achieved by using an isolated execution environment in which any communication with the outside untrusted world is forcibly encrypted by trusted hardware. The mechanism can be useful to overcome the challenging issues in guaranteeing confidential execution in virtualized infrastructures, including cloud computing and virtualized network functions, among other scenarios. Moreover, the proposed mechanism does not suffer from the performance drawbacks typical of other solutions proposed for secure computing, as highlighted by the presented novel validation results. Copyright © 2014 SCITEPRESS - Science and Technology Publications

Access Control for the Pepys Internet-Wide File-System

This paper describes the Access Control Model realized for the novel Pepys distributed, Internet-wide, file-system. The model design has been widely inspired to various existing standards and best practices about access control and security in file-system access, but it also echoes peculiar basic principles characterizing the design of Pepys, as well as the ΠP protocol, over which Pepys itself relies. The paper also provides technical details about how the model has been realized on a Linux port of Pepys

Optimum Allocation of Distributed Service Workflows with Probabilistic Real-Time Guarantees

This paper addresses the problem of optimum allocation of distributed real-time workflows with probabilistic service guarantees over a set of physical resources. The discussion focuses on how such a problem may be mathematically formalized, in terms of both constraints and objective function to be optimized, which also accounts for possible business rules for regulating the deployment of the workflows. The presented formal problem constitutes a probabilistic admission control test that may be run by a provider in order to decide whether or not it is worth to admit new workflows into the system and to decide what the optimum allocation of the workflow to the available resources is. Various options are presented, which may be plugged into the formal problem description, depending on the specific needs of individual workflows. The presented problem has been implemented using GAMS and has been tested under various solvers. An illustrative numerical example and an analysis of the results of the implemented model under realistic settings are presented