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Writing a new scheduler and integrating it into an exist-ing OS is a daunting task, requiring the understanding of multiple low-level kernel mechanisms. Indeed, implementing a new scheduler is outside the expertise of application programmers, even though they are the ones who understand best the scheduling needs of their applications.To address these problems, we present the design of Bossa, a language targeted toward the development of scheduling policies. Bossa provides high-level abstractions that are specific to the domain of scheduling. These constructs simplify the task of specifying a new scheduling policy and facilitate the static verification of critical safety properties.We illustrate our approach by presenting an implementation of the EDF scheduling policy. The overhead of Bossa is acceptable. Overall, we have found that Bossa simplifies scheduler development to the point that kernel expertise is not required to add a new scheduler to an existing kernel.

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Standard operating systems provide only a single fixed scheduler, which does not meet all possible application scheduling needs. More flexibility can be achieved using a hierarchy of schedulers, allowing multiple schedulers to coexist in a single operating system (OS). Bossa is a framework for facilitating the implementation and deployment of OS process schedulers. In this paper, we describe the features of Bossa that enable the creation and management of a scheduling hierarchy. These features include a domain-specific language for implementing schedulers and a type system for describing requirements on scheduler behavior. The use of the domainspecific language eases scheduler development and enables scheduler verification. We have found that the approach allows programmers, even students who are not kernel or scheduling experts, to easily and safely implement and deploy schedulers that meet specific application needs.