Compile/Run-time Support for Threaded MPI Execution on Multiprogrammed Shared Memory Machines Hong Tang, Kai Shen, and Tao Yang Department of Computer Science University of California, Santa Barbara CA93116 MPI is a message-passing standard widely used for developing high-performance parallel applications. Because of the restriction in the MPI computation model, conventional implementations on shared memory machines map each MPI node to an OS process, which suffers serious performance degradation in the presence of multiprogramming, especially when a space/time sharing policy is employed in OS job scheduling. In this paper, we study compile-time and run-time support for MPI by using threads and demonstrate our optimization techniques for executing a large class of MPI programs written in C. The compile-time transformation adopts thread-specific data structures to eliminate the use of global and static variables in C code. The run-time support includes an efficient point-to-point communication protocol based on a novel lock-free queue management scheme. Our experiments on SGI Origin2000 show that the MPI execution optimized by using the proposed techniques is competitive with SGI's native MPI implementation in dedicated environments, and has great performance advantages with upto 23-fold improvement in multiprogrammed environments.