Several modern multi-core architectures support the dynamic control of the CPU's clock rate, allowing processor cores to temporarily operate at speeds exceeding the operational base frequency. Conversely, cores can operate at a lower speed or be disabled altogether to save power. Such facilities are notably provided by Intel's Turbo Boost and AMD's Turbo CORE technologies. Frequency control is typically driven by the operating system which requests changes to the performance state of the processor based on the current load of the system. In this paper, we investigate the use of dynamic frequency scaling from user space to speed up multi-threaded applications that must occasionally execute time-critical tasks or to solve problems that have heterogeneous computing requirements. We propose a general-purpose library that allows selective control of the frequency of the cores - subject to the limitations of the target architecture. We analyze the performance trade-offs and illustrate its benefits using several benchmarks and real-world workloads when temporarily boosting selected cores executing time-critical operations. While our study primarily focuses on AMD's architecture, we also provide a comparative evaluation of the features, limitations, and runtime overheads of both Turbo Boost and Turbo CORE technologies. Our results show that we can successful exploit these new hardware facilities to accelerate the execution of key sections of code (critical paths) improving overall performance of some multi-threaded applications. Unlike prior research, we focus on performance instead of power conservation. Our results further can give guidelines for the design of hardware power management facilities and the operating system interfaces to those facilities.

Several modern multi-core architectures support the dynamic control of the CPU's clock rate, allowing processor cores to temporarily operate at speeds exceeding the operational base frequency. Conversely, cores can operate at a lower speed or be disabled altogether to save power. Such facilities are notably provided by Intel's Turbo Boost and AMD's Turbo CORE technologies. Frequency control is typically driven by the operating system which requests changes to the performance state of the processor based on the current load of the system. In this paper, we investigate the use of dynamic frequency scaling from user space to speed up multi-threaded applications that must occasionally execute time-critical tasks or to solve problems that have heterogeneous computing requirements. We propose a general-purpose library that allows selective control of the frequency of the cores - subject to the limitations of the target architecture. We analyze the performance trade-offs and illustrate its benefits using several benchmarks and real-world workloads when temporarily boosting selected cores executing time-critical operations. While our study primarily focuses on AMD's architecture, we also provide a comparative evaluation of the features, limitations, and runtime overheads of both Turbo Boost and Turbo CORE technologies. Our results show that we can successful exploit these new hardware facilities to accelerate the execution of key sections of code (critical paths) improving overall performance of some multi-threaded applications. Unlike prior research, we focus on performance instead of power conservation. Our results further can give guidelines for the design of hardware power management facilities and the operating system interfaces to those facilities.

A significant portion of the memory in servers today is often unused. Our large-scale study of HPC systems finds that more than half of the total memory in active nodes running user jobs are unused for 88% of the time. Google and Azure Cloud studies also report unused memory accounts for 40% of the total memory in their servers, on average. Leaving so much memory unused is wasteful. To address this problem, we note that in the context of CPUs, Turbo Boost can turn off the unused cores to boost the performance of in-use cores. However, there is no equivalent technology in the context of memory; no matter how much memory is unused, the performance of in-use memory remains the same. This dissertation explores architectural techniques to utilize the unused memory to boost the performance of in-use memory and refer to them collectively as Memory Turbo Boost. This dissertation explores how to turbo boost memory performance through memory replication; specifically, it explores how to efficiently store the replicas in the unused memory and explores multiple architectural techniques to utilize the replicas to enhance memory system performance. Performance simulations show that Memory Turbo Boost can improve node-level performance by 18%, on average across a wide spectrum of workloads. Our system-wide simulations show applying Memory Turbo Boost to an HPC system provides 1.4x average speedup on job turnaround time. / Doctor of Philosophy / Today's servers often have a significant portion of their memory unused. Our large-scale study of HPC systems finds that more than half of the total memory of an HPC server is unused for most of the time; Google and Azure Cloud studies find that 40% of the total memory in their servers is often unused. Today's servers usually have 100s of GBs to TB memory; 40% unused memory means 10s-100s of GBs unused memory on the servers. Leaving so much memory unused is wasteful. To address this problem, I note that there are techniques to leverage unused hardware resources to improve the performance of in-use resources in other types of hardware. For example, CPU Turbo Boost can turn off the unused cores to boost the performance of in-use cores; modern SSDs can use the unused space to switch the Multi-Level Cell blocks to Single-Level Cell blocks to boost performance. However, there is no equivalent technology in the context of memory; no matter how much memory is unused, the performance of in-use memory remains the same. This dissertation explores techniques to utilize the unused memory to boost the performance of in-use memory and refer to them collectively as Memory Turbo Boost. Performance evaluations show that Memory Turbo Boost can provide up to 18% average performance improvement.