1,720,972 research outputs found
Improving Responsiveness for Virtualized Networking Under Intensive Computing Workloads
No full textIn this paper the problem of providing network response guarantees to multiple Virtual Machines (VMs) co-scheduled on the same set of CPUs is tackled, where the VMs may have to host both responsive real-time applications and batch compute-intensive workloads. When trying to use a real-time reservation- based CPU scheduler for providing stable performance guarantees to such a VM, the compute-intensive workload would be scheduled better with high time granularities, to increase performance and reduce system overheads, whilst the real-time workload would need lower time granularities in order to keep the response-time under acceptable levels. The mechanism that is proposed in this paper mixes both concepts, allowing the scheduler to dynamically switch between fine-grain and coarse-grain scheduling intervals depending on whether the VM is performing network operations or not. A prototype implementation of the proposed mechanism has been realized for the KVM hypervisor when running on Linux, modifying a deadline-based real-time scheduling strategy for the Linux kernel developed previously. The gathered experimental results show that the proposed technique is effective in controlling the response-times of the real-time workload inside a VM while at the same time it allows for an efficient execution of the batch compute-intensive workload
Real-Time Issues in Live Migration of Virtual Machines
No full textThis paper addresses the issue of how to meet the strict timing constraints of (soft) real-time virtualized applications while the Virtual Machine (VM) hosting them is undergoing a live migration. To this purpose, it is essential that the resource requirements of a migration are identified in advance, that appropriate resources are reserved to the process, and that multiple VMs sharing the same resources are temporally isolated from each other. The first issue is dealt with by introducing a stochastic model for the migration process. The other ones by introducing a methodology making use of proper scheduling algorithms (for both CPU and network) that allow for reserving resource shares to individual VMs. Also, an extensive set of simulations have been done by using traces of a VLC video server virtualized by using KVM on Linux. The traces have been obtained by patching KVM at the kernel level, and the same patch constitutes an important step towards the complete implementation of the proposed technique. The obtained results highlight the benefits of the proposed approach
Effective Real-Time Computing on Linux
No full textIn this paper we present an architecture design for supporting real time computing on Linux. This architecture focuses on improving the usability of real time capabilities for applications by providing a unified Application Programming Interface. Applications can therefore use it without having to know exactly what the underlying scheduling algorithm is. Still, the real-time computing capabilities of the platform may be exploited to the maximum extent. The main aim of the paper is to gather feedback from the community about the design and directions for development
Adaptive Real-Time Scheduling for Legacy Multimedia Applications
No full textMultimedia applications are often executed on standard Personal Computers. The absence of established standards has hindered the adoption of real-time scheduling solutions in this class of applications. Developers have adopted a wide range of heuristic approaches to achieve an acceptable timing behaviour but the result is often unreliable. We propose a mechanism to extend the benefits of real-time scheduling to legacy applications based on the combination of two techniques: 1) a real-time monitor that observes and infers the activation period of the application, and 2) a feedback mechanism that adapts the scheduling parameters to improve its real-time performance
Self-tuning Schedulers for Legacy Real-Time Applications
No full textWe present an approach for adaptive scheduling of soft real-time legacy applications (for which no timing information is exposed to the system). Our strategy is based on the combination of two techniques: 1) a real-time monitor that observes the sequence of events generated by the application to infer its activation period, 2) a feedback mechanism that adapts the scheduling parameters to ensure a timely execution of the application. By a thorough experimental evaluation of an implementation of our approach, we show its performance and its efficiency
The Wizard of OS: a Heartbeat for Legacy Multimedia Applications
No full textMultimedia applications are often characterised by implicit temporal constraints but, in many cases, they are not programmed using any specialised real-time API. These "Legacy applications" have no way to communicate their temporal constraints to the OS kernel, and their quality of service (QoS), being necessarily linked to the temporal behaviour, fails to satisfy acceptable standards. In this paper we propose an innovative way for dealing with these applications, based on the combination of an on-line identification mechanism (which extracts from high-level observations such important parameters as the execution rate) and an adaptive scheduler (specialised for legacy applications) that identifies the correct amount of CPU needed by each application. Preliminary experimental results are reported, proving the effectiveness of the proposed idea in providing a widely used multimedia player on Linux with appropriate QoS guarantees, through an appropriate choice of the scheduling parameters. Finally, a detailed road-map is presented with the possible extensions to the approach
Distributed Interactive Real-time Multimedia Applications: A Sampling and Analysis Framework
No full textThe advancements in distributed computing have driven the emergence of service-based infrastructures that allow for on-demand provision of IT assets. However, the complexity of characterizing an application’s behavior, and as a result the potential offered level of Quality of Service (QoS), introduces a number of challenges in the data collection and analysis process on the Service Providers’ side, especially for real time applications. The aforementioned complexity is increased due to additional factors that influence the application’s behavior, such as real time scheduling decisions, percentage of a node assigned to the application or application-generated workload. In this paper, we present a framework developed under the IRMOS EU-funded project that enables the sampling and gathering of the necessary dataset in order to analyze an application’s behavior. Processing of the resulting dataset is also conducted in order to extract useful conclusions regarding CPU allocation and scheduling decisions effect on the QoS. We demonstrate the operation of the proposed framework and evaluate its performance and effectiveness using an interactive real-time multimedia application, namely a webbased eLearning scenario
Sporadic Server Revisited
No full textThe Sporadic Server (SS) overcomes the major limitations of other Resource Reservation Fixed Priority based techniques, but it also presents some drawbacks, mainly related to an increased scheduling overhead and a not so efficient behavior during overrun situations.In this paper we introduce and prove the effectiveness of an improved SS with reduced overhead and fairer handling of server overrun situations. We also show how this can be efficiently exploited to provide temporal isolation in a multiprocessor platform, adapting already existing schedulability tests
Providing Performance Guarantees to Virtual Machines Using Real-Time Scheduling
No full textIn this paper we tackle the problem of providing Quality of Service guarantees to virtualized applications, focusing on computing and networking guarantees. We propose a mechanism for providing temporal isolation based on a CPU real time scheduling strategy. This allows not only to have control over the individual virtual machine throughput, but also on the activation latency and response-time by which virtualized software components react to external events. We show experimental results gathered on a real system validating the approach
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