The widening gap between processor speed and memory latency will continue to be a critical issue to the performance of computer systems. The latency problem is even more acute on multiprocessors that share the same space, in which a main memory module is typically remote to all or all but one of the processors. It is therefore important to reduce unnecessary remote memory references and unnecessary network activities, and to achieve high hit ratio at the private, primary caches. The project explores coherent designs of compilers and memory architectures to improve the average memory latency, and the network traffic. The main thrust of this work is to combine compilers' ability to predict program behavior with harrdware's ability to record memory reference patterns at run time. The research focuses on three major issues: (1) The use of a compiler-assisted and hardware controlled coherence mechanism on multiprocessors with private cache memories; (2) The use of sophisticated interprocedural analysis to support the proposed coherence mechanism, via array data flow analysis and static task scheduling; and (3) The effects of program transformations, false sharing and limited directory pointers on the proposed coherence mechanism. This work covers a variety of multiprocessors that share a common address space, including bus-based systems, the Non-Uniform Access (NUMA) multiprocessors and the Cache-Only Memory Access (COMA) multiprocessors. The main objectives of the PI's education plan in this funding period are (1) to redesign the compiler and language design course sequence for the Computer Science Department of Minnesota and to solidify the interfaces of these sources with other language design sources; (2) to augment the main compiler and language design sources by seminar courses which address new issues regarding the interfaces of the compilers with the rest of the computer systems, and (3) to achieve teaching excellence in these c ourses so as to provide students solid understanding of the principles of programming language design and implementation and compiler techniques which will be important to their scientific and engineering career. The PI will conduct two experiments in this funding period. One is to develop a language design source to be taught after the compiler courses and the other is to add an operating system implementation course to the curriculum. Additional educational activities of the PI include exploration of new avenues for creating industry co-op programs for students in the computer systems area and exploration of new avenues or providing professionals with excellent access to both the basic courses and the seminar courses, e.g. through the university's Distributed Multimedia Learning Center.
