Hardware Support for Multithreaded Execution of Loops with Limited Parallelism

Loop scheduling has significant differences in multithreaded from other parallel processors. The sharing of hardware resources imposes new scheduling limitations, but it also allows a faster communication across threads. We present a multithreaded processor model, Coral 2000, with hardware extensions that support Macro Software Pipelining, a loop scheduling technique for multithreaded processors. We tested and evaluated Coral 2000 on a cycle-level simulator, using synthetic and integer SPEC benchmarks. We obtained speedups of up to 30% with respect to highly optimized superblock-based schedules on loops that exhibit limited parallelism.