Using Software-extended Architectures for Software Simultaneous Multithreading

A software-extended architecture (SEA) enhances a hardware architecture by placing a high-performance dynamic instruction-set translator between the application binary and the processor, improving processor utilization and enabling new functionality with no changes to either the processor or the binaries. Our prototype implementation of a software-extended Alpha 21164 can provide new system functionality while adding only 1%{30% to the running time of an application. Using this prototype, we have implemented software simultaneous multithreading (SSMT), a new software technique for allowing programs to make greater use of the processor pipeline. SSMT merges instruction streams from independent processes, in order to increase instruction-level parallelism. Experiments with SSMT on the software-extended Alpha 21164 show that processor throughput can be improved by up to 30% on real programs, despite the small number of issue slots on this processor.