Steven K. Reinhardt, Babak Falsafi, and David A. Wood
Computer Sciences Department
University of Wisconsin--Madison
The executive interface was motivated by the requirements of the Wisconsin Wind Tunnel (WWT), a system for evaluating cache-coherent shared-memory parallel architectures. WWT uses the executive interface to implement a fine-grain user-level extension of Li's shared virtual memory on a Thinking Machines CM-5, a message-passing multicomputer. However, the interface is sufficiently general that an executive could act as a multiprogrammed operating system, exporting an alternative interface to the threads running in its subservient contexts.
The executive interface is currently implemented as an extension to CMOST, the standard operating system for the CM-5. In CMOST, policy decisions are made on a central, distinct control processor (CP) and broadcast to the processing nodes (PNs). The PNs execute a minimal kernel sufficient only to implement the CP's policy. While this structure efficiently supports some parallel application models, the lack of autonomy on the PNs restricts its generality. Adding the executive interface provides limited autonomy to the PNs, creating a structure that supports multiple models of application parallelism. This structure, with autonomy on top of centralization, is in stark contrast to most microkernel-based parallel operating systems in which the nodes are fundamentally autonomous.
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