Chip multithreading systems need a new operating system scheduler

The unpredictable nature of modern workloads, characterized by frequent branches and control transfers, can result in processor pipeline utilization as low as 19%. Chip multithreading (CMT), a processor architecture combining chip multiprocessing and hardware multithreading, is designed to address this issue. Hardware vendors plan to ship CMT systems within the next two years; understanding how such systems will perform is crucial if we are to use them to full advantage.Our simulation experiments show that a CMT-savvy operating system scheduler could improve application performance by a factor of two. In this paper we describe our initial analysis of application performance on CMT systems and propose a design for a scheduler tailored for the needs of a CMT system.