Cooperative Shared Memory and the Wisconsin Wind Tunnel

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Hill The goal of this project is to design hardware and software for scalable shared-address-space computers. Cooperative shared memory, the approach taken in the project, provides a simple design for shared-memory hardware and a programming model that can be used by programmers and compilers to understand an application's communication behavior. Cooperative shared memory uses simple directory hardware together with a set of pragmas for use in applications software. The pragmas allow the applications software to indicate which processors will be using a block of memory: a processor can check out a block when it expects frequent use, check it back in when it is done, and can indicate that it expects to check out a block in the near future. Simple directory hardware can be used to place checked-out-memory locations in the caches of the appropriate processors. Common state transitions in the directory protocol are implemented in hardware, while the less common ones use software traps. Note that the pragmas and the resulting hardware actions affect only the execution speed of a program, not its correctness. A new virtual prototyping approach is being used for evaluating the new architecture. The Wisconsin Wind Tunnel runs parallel shared-memory programs on a parallel message-passing computer and concurrently evaluates the programs execution times on proposed hardware using a distributed simulation. The simulation runs quickly because instructions that make only local memory references are executed directly.