A Framework for Problem - Specific QoS Based Scheduling in Grids 2

Grid computing is generally viewed as task assignment to distributed resources. While in practice many factors do complicate this scheduling process (e.g. resource monitoring and discovery, resource failures, resources ownership and policies ... etc), the process is still viewed as resource scheduling according to some criteria. The criteria are referred to as Quality of Service (QoS) attributes in grid computing context. QoS in general are non-functional characters describing a process. QoS attributes are divided into two main groups, namely objective QoS and subjective QoS. Objective QoS attributes are used to specify performance parameters including timeliness, precision, accuracy, security requirements and availability. Subjective QoS attributes, on the other hand, capture application specific policies that govern how an application is treated by the resourcemanager. In this chapter, objective QoS attributes are referred to as basic QoS attributes, while subjective QoS attributes are referred to as application-specific QoS attributes. In comparison to application-specific QoS attributes, a huge legacy of schedulingwith the basic QoS attributes exists. This chapter proposes adopting application-specific QoS attributes to define new criteria other than the basic ones to enhance the preference of which resources to choose in the task assignment process as the QoS attributes are application-specific (e.g. a Grid application involving service tasks that retrieve images from a service resource could have the color depth and resolution as QoS attributes). For grid computing to go beyond the basic QoS attributes the following challenges need to be addressed: a) A method to formally define new application-specific QoS attributes. b) A method to measure the QoS attribute fidelity of a specific resource. c) Scheduling the tasks over the resources taking into consideration the defined application-specific QoS attributes. This chapter addresses these challenges and proposes a framework that starts from defining new application-specific QoS attributes until the tasks are executed over the resources. As for the first challenge, a system for defining QoS using a formal language is inspired fromCanfora et al. (2006) which proposes service composition binding driven by application-specific QoS. The domain of Canfora et al. (2006) is different from the work in this chapter. This is because the authors are concerned with the composition of services that are initially defined as an abstract workflow, where for each service in the workflow a set of service providers are defined. Then the scheduler/binder makes a concrete workflow at which each service in the abstract workflow is bind to a service provider. Canfora et al. addressed how application A Framework for Problem-Specific QoS Based Scheduling in Grids 2