The Kernel Tool Kit ( K T K ) is an object-based operating system kernel and parallel programming library that offers explicit support f o r on-and off-line program configuration. Specifically, K T K allows the specification of attributes f o r object classes, object instances, state variables, operations and object invocations. Attributes are interpreted by policy classes that m a y be varied separately f r o m the abstractions with which they are associated. They can be used to vary object internal implementation and semantics without affecting the methods being invoked. In this paper, the runtime configuration of K T K attributes is shown to improve the runtime performance of multiprocessor applications. K T K is layered on a portable and configurable parallel programming substrate, a Mach Cthreads compatible runtime library[22]. ConclusionsKTK and configurable threads provide an efficient basis for building configurable operating system kernels and application programs for multiprocessor systems. The performance advantages demonstrated 4 A configuration action is based on lock state that is 'too old' due to the relatively slow and asynchronous communication between applications threads and the local monitor thread.