دانلود رایگان ترجمه مقاله میان افزار قابل تنظیم برای سیستم زمان واقعی توزیع شده با وظایف بلافاصله و دوره ای – IEEE 2010

میان افزار قابل پیکربندی برای سیستم های زمان-واقعی توزیع شده با وظایف متناوب و غیرمتناوب

Configurable Middleware for Distributed Real-Time Systems with Aperiodic and Periodic Tasks

چکیده 

سیستم های زمان-واقعی توزیع شده مختلف (DRS) باید رویدادهای متناوب و غیرمتناوب را تحت مجموعه ای متناوب از الزامات (شرایط) رفع و رجوع نمایند. در حالیکه میان افزار موجود مانند CORBA زمان-واقعی, به عنوان یک سیستم عامل برای سیستم های توزیع شده با محدودیت های زمانی نویدبخش بوده است, اما فاقد مکانیزم های پیکربندی انعطاف پذیری مورد نیاز برای مدیریت زمانبندی آسان سر هم پیوسته برای گستره وسیعی از DRS مختلف با رویدادهای متناوب و غیرمتناوب است. سهم اولیه این کار, طراحی, پیاده سازی, و ارزیابی عملکرد اولین خدمات میان افزار مولفه قابل پیکربندی برای کنترل پذیرش و تعادل بار رفع و رجوع رویداد متناوب و غیرمتناوب در DRS است. نتایج تجربی, نیاز و اثربخشی رویکرد میان افزار مولفه قابل پیکربندی ما را در حمایت از کاربردهای مختلف با رویدادهای متناوب و غیرمتناوب نشان می دهند و یک سیستم عامل نرم افزار انعطاف پذیر برای DRS با محدودیت های زمانبندی سر هم پیوسته را فراهم می کند.

Abstract

Different distributed real-time systems (DRS) must handle aperiodic and periodic events under diverse sets of requirements. While existing middleware such as Real-Time CORBA has shown promise as a platform for distributed systems with time constraints, it lacks flexible configuration mechanisms needed to manage end-to-end timing easily for a wide range of different DRS with both aperiodic and periodic events. The primary contribution of this work is the design, implementation, and performance evaluation of the first configurable component middleware services for admission control and load balancing of aperiodic and periodic event handling in DRS. Empirical results demonstrate the need for, and the effectiveness of, our configurable component middleware approach in supporting different applications with aperiodic and periodic events, and providing a flexible software platform for DRS with end-to-end timing constraints.

1 INTRODUCTION

MANY distributed real-time systems (DRS) must handle a mix of aperiodic and periodic events, including aperiodic events with end-to-end deadlines whose assurance is critical to the correct behavior of the system. Requirements for increased software productivity and quality motivate the use of open distributed object computing (DOC) middleware such as CORBA, rather than building applications entirely from scratch using proprietary methods. The use of CORBA middleware has increased significantly in DRS domains such as aerospace, telecommunications, medical systems, distributed interactive simulations, and computer-integrated manufacturing, which are also characterized by stringent quality of service (QoS) requirements [1]. For example, in an industrial plant monitoring system, an aperiodic alert may be generated when a series of periodic sensor readings meets certain hazard detection criteria. This alert must be processed on multiple processors within an end-to-end deadline, e.g., to put an industrial process into a fail-safe mode. User inputs and other sensor readings may trigger other real-time aperiodic events. While traditional real-time middleware solutions such as Real-Time CORBA [2] and Real-Time Java [3] have shown promise as distributed software platforms for systems with time constraints, existing middleware systems lack the flexibility needed to support DRS with diverse application semantics and requirements. For example, load balancing is an effective mechanism for handling variable real-time workloads in a DRS. However, its suitability for DRS highly depends on their application semantics. Some digital control algorithms (e.g., proportional-integral-derivative control) for physical systems are stateful and hence not amenable for frequent task reallocation caused by load balancing, while others (e.g., proportional control) do not have such limitations. Similarly, job skipping (skipping the processing of certain instances of a periodic task) is useful for dealing with transient system overload. While job skipping is not suitable for certain critical control applications in which missing one job may cause catastrophic consequences on the controlled system, other applications ranging from video reception to telecommunications may be able to tolerate varying degrees of job skipping [4]. Therefore, a key open challenge for DRS is to develop a flexible middleware infrastructure that can be easily configured to support the diverse requirements of different DRS. Specifically, middleware services such as load balancing and admission control must support a variety of alternative strategies (algorithms and inputs corresponding to those algorithms). Furthermore, the configuration of those strategies must be supported in a flexible yet principled way, so that system developers are able to explore alternative configurations without choosing invalid configurations by mistake. Providing middleware services with configurable strategies, thus, faces several important challenges: 1) services must be able to provide configurable strategies, and configuration tools must be added or extended to allow configuration of those strategies; 2) the specific criteria that distinguish which service strategies are preferable must be identified, and applications must be categorized according to those criteria; and 3) appropriate combinations of services’ strategies must be identified for each such application category, according to its characteristic criteria. To address these challenges, and thus to enhance support for diverse DRS with aperiodic and periodic events, we have designed and implemented a new set of component middleware services including end-to-end event scheduling, admission control, and load balancing. We have also developed configuration tools to integrate these service components for each particular application according to its specific criteria. Research contributions. In this work, we have 1. developed what is to our knowledge the first set of configurable component middleware services supporting multiple admission control and load balancing strategies for handling aperiodic and periodic events; 2. developed a novel component configuration preparser and interfaces to configure real-time admission control and load balancing services flexibly at system deployment time; 3. defined categories of distributed real-time applications according to specific characteristics, and related them to suitable combinations of strategies for our services; and 4. provided a case study that applies different configurable services to a domain with both aperiodic and periodic events, offers empirical evidence of the overheads involved and the trade-offs among service configurations, and demonstrates the effectiveness of our approach in that domain. Our work, thus, significantly enhances the applicability of real-time middleware as a flexible infrastructure for DRS. Section 2 introduces the middleware systems and scheduling theory underlying our approach. Sections 3-5 present our middleware architecture, configurable strategies, and component implementations for supporting endto-end event handling in DRS. Section 6 describes our new configuration engine extensions, which can flexibly configure different strategies for our services according to each application’s requirements. Section 7 evaluates the performance of our approach, including trade-offs among different service strategy combinations, and characterizes the overheads introduced by our approach. Section 8 presents a survey of related work, and we offer concluding remarks in Section 9.