OS-aware architecture for improving microprocessor performance and energy efficiency

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Li, Tao

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The Operating System (OS) which manages both hardware and software resources, constitutes a major component of today’s complex systems implemented with high-end and general-purpose microprocessors, memory hierarchy and heterogeneous I/O devices. Modern and emerging applications (e.g., database, web servers and file/e-mail workloads) exercise the OS significantly. However, microprocessor designs and (performance/power) optimizations have largely ignored the impact of OS. This dissertation characterizes the OS activity in emerging applications execution and demonstrates the necessity, advantages, and benefits of integrating OS component in processor architecture design. It is essential to understand the characteristics of today’s emerging workloads in order to design efficient architectures for them. Given the facts that modern and emerging applications involve system activities significantly, this research uses complete system evaluation. These evaluations result in several system performance and power optimizations targeting for emerging applications that have heavier OS activity. The OS dissipates a significant portion of total power in many modern application executions. Therefore, modeling OS power is imperative for accurate software power evaluation, as well as power management (e.g. dynamic thermal control and equal energy scheduling). This research characterizes the power behavior of a modern, commercial OS across a wide spectrum of applications to understand OS energy profiles and then proposed various models to cost-effectively estimate its run-time energy dissipation. To reduce software power, hardware can provide resources that closely match the needs of the software. However, with exception-driven and intermittent execution in nature, it becomes difficult to accurately predict and adapt processor resources in a timely fashion for OS power savings without significant performance degradation. This dissertation proposes a methodology that permits precise processor adaptations for the operating system with low overhead. Low power has been considered as an important issue in instruction cache (Icache) designs. This research goes beyond previous work to explore the opportunities to design energy-efficient I-cache by exploiting the interactions of hardware-OSapplications. This dissertation presents two techniques (OS-aware cache way lookup and OS-aware cache set drowsy mode) to reduce the dynamic and the static power consumption of I-cache. The proposed mechanisms require minimal hardware modification and addition. The OS component affects the control flow transfer in the execution environment because the exception-driven, intermittent invocation of OS code significantly increases the misprediction in both user and kernel code. This indicates that to improve microprocessor performance, adapting branch prediction hardware for OS has become very important now. This research proposes two OS-aware branch prediction techniques to alleviate this destructive impact.