Scheduling of processes onto processors of a parallel machine has always been an important and challenging area of research. The issue becomes even more crucial and difficult as we gradually progress to the use of off-the-shelf workstations, operating systems, and high bandwidth networks to build cost-effective clusters for demanding applications. Clusters are gaining acceptance not just in scientific applications that need supercomputing power, but also in domains such as databases, web service and multimedia, which place diverse Qualityof-Service (QoS) demands on the underlying system. Further, these applications have diverse characteristics in terms of their computation, communication and I/O requirements, making conventional parallel scheduling solutions, such as space sharing or coscheduling, unattractive. At the same time, leaving it to the native operating system of each node to make decisions independently can lead to ineffective use of system resources whenever there is communication. Instead, an emerging class of dynamic coscheduling mechanisms, that attempt to take remedial actions to guide the system towards coscheduled execution without requiring explicit synchronization, offers a lot of promise for cluster scheduling. Using a detailed simulator, this paper evaluates the pros and cons of different dynamic coscheduling alternatives, while comparing their advantages over traditional coscheduling (and not performing any coordinated

In this paper, we examine two architectural alternatives— native OS support versus middleware—for supporting multimedia applications. Specifically, we examine whether extensions to OS functionality are necessary for supporting multimedia applications, or whether much of these benefits can be accrued by implementing resource management mechanisms in a middleware system. To answer these questions, we use QLinux and TAO as representative examples of a multimedia operating system and a multimedia middleware, respectively, and examine their effectiveness in supporting distributed applications. Our results show that although the run-time overheads of a middleware can impact application performance, middleware resource management mechanisms can, nevertheless, be as effective as native OS mechanisms for many applications. We also find OS kernelbased mechanisms to be more effective then middleware systems at providing application isolation and at preventing applications from interfering with one another.