Abstract—One of the key challenges for improving efficiency in warehouse scale computers (WSCs) is to improve server utilization while guaranteeing the quality of service (QoS) of latency-sensitive applications. To this end, prior work has proposed techniques to precisely predict performance and QoS interference to identify ‘safe ’ application co-locations. However, such techniques are only applicable to resources shared across cores. Achieving such precise interference prediction on real-system simultaneous multithreading (SMT) architectures has been a significantly challenging open problem due to the complexity introduced by sharing resources within a core. In this paper, we demonstrate through a real-system in-vestigation that the fundamental difference between resource sharing behaviors on CMP and SMT architectures calls for a redesign of the way we model interference. For SMT servers, the interference on different shared resources, including private caches, memory ports, as well as integer and floating-point functional units, do not correlate with each other. This insight suggests the necessity of decoupling interference into multiple resource sharing dimensions. In this work, we propose SMiTe, a methodology that enables precise performance prediction for SMT co-location on real-system commodity processors. With a set of Rulers, which are carefully designed software stressors that apply pressure to a multidimensional space of shared resources, we quantify application sensitivity and contentiousness in a decoupled manner. We then establish a regression model to combine the sensitivity and contentiousness in different dimensions to predict performance interference. Using this methodology, we are able to precisely predict the performance interference in SMT co-location with an average error of 2.80 % on SPEC CPU2006 and 1.79 % on CloudSuite. Our evaluation shows that SMiTe allows us to improve the utilization of WSCs by up to 42.57 % while enforcing an application’s QoS requirements. Keywords-quality of service; simultaneous multithreading; datacenter; warehouse scale computer I.

As user demand scales for intelligent personal assistants (IPAs) such as Apple’s Siri, Google’s Google Now, and Microsoft’s Cortana, we are approaching the computational limits of current datacenter architectures. It is an open ques-tion how future server architectures should evolve to enable this emerging class of applications, and the lack of an open-source IPA workload is an obstacle in addressing this ques-tion. In this paper, we present the design of Sirius, an open end-to-end IPA web-service application that accepts queries in the form of voice and images, and responds with natu-ral language. We then use this workload to investigate the implications of four points in the design space of future accelerator-based server architectures spanning traditional

Abstract — Heterogeneous multicore architectures have the po-tential to improve energy efficiency by integrating power-efficient wimpy cores with high-performing brawny cores. However, it is an open question as how to deliver energy reduction while ensuring the quality of service (QoS) of latency-sensitive web-services running on such heterogeneous multicores in warehouse-scale computers (WSCs). In this work, we first investigate the implications of hetero-geneous multicores in WSCs and show that directly adopting heterogeneous multicores without re-designing the software stack to provide QoS management leads to significant QoS violations. We then present Octopus-Man, a novel QoS-aware task manage-ment solution that dynamically maps latency-sensitive tasks to the least power-hungry processing resources that are sufficient to meet the QoS requirements. Using carefully-designed feedback-control mechanisms, Octopus-Man addresses critical challenges that emerge due to uncertainties in workload fluctuations and adaptation dynamics in a real system. Our evaluation using web-search and memcached running on a real-system Intel het-erogeneous prototype demonstrates that Octopus-Man improves energy efficiency by up to 41 % (CPU power) and up to 15% (system power) over an all-brawny WSC design while adhering to specified QoS targets. I.

Abstract—Reducing the long tail of the query latency dis-tribution in modern warehouse scale computers is critical for improving performance and quality of service of workloads such as Web Search and Memcached. Traditional turbo boost increases a processor’s voltage and frequency during a coarse-grain sliding window, boosting all queries that are processed during that window. However, the inability of such a technique to pinpoint tail queries for boosting limits its tail reduction benefit. In this work, we propose Adrenaline, an approach to lever-age finer granularity, 10’s of nanoseconds, voltage boosting to effectively rein in the tail latency with query-level precision. Two key insights underlie this work. First, emerging finer granularity voltage/frequency boosting is an enabling mechanism for intelli-gent allocation of the power budget to precisely boost only the queries that contribute to the tail latency; and second, per-query characteristics can be used to design indicators for proactively pinpointing these queries, triggering boosting accordingly. Based on these insights, Adrenaline effectively pinpoints and boosts queries that are likely to increase the tail distribution and can reap more benefit from the voltage/frequency boost. By evaluating under various workload configurations, we demonstrate the effectiveness of our methodology. We achieve up to a 2.50x tail latency improvement for Memcached and up to a 3.03x for Web Search over coarse-grained DVFS given a fixed boosting power budget. When optimizing for energy reduction, Adrenaline achieves up to a 1.81x improvement for Memcached and up to a 1.99x for Web Search over coarse-grained DVFS. I.

Datacenters, or warehouse scale computers, are rapidly increasing in size and power consumption. However, this growth comes at the cost of an increasing thermal load that must be removed to prevent overheating and server failure. In this paper, we propose to use phase changing materials (PCM) to shape the thermal load of a datacenter, absorbing and releasing heat when it is advantageous to do so. We present and validate a methodology to study the impact of PCM on a datacenter, and evaluate two important opportunities for cost savings. We find that in a datacenter with full cooling system subscription, PCM can reduce the necessary cooling system size by up to 12 % without impacting peak throughput, or increase the number of servers by up to 14.6 % without increasing the cooling load. In a thermally constrained setting, PCM can increase peak throughput up to 69 % while delaying the onset of thermal limits by over 3 hours. 1.

Abstract—Reducing the long tail of the query latency dis-tribution in modern warehouse scale computers is critical for improving performance and quality of service of workloads such as Web Search and Memcached. Traditional turbo boost increases a processor’s voltage and frequency during a coarse-grain sliding window, boosting all queries that are processed during that window. However, the inability of such a technique to pinpoint tail queries for boosting limits its tail reduction benefit. In this work, we propose Adrenaline, an approach to lever-age finer granularity, 10’s of nanoseconds, voltage boosting to effectively rein in the tail latency with query-level precision. Two key insights underlie this work. First, emerging finer granularity voltage/frequency boosting is an enabling mechanism for intelli-gent allocation of the power budget to precisely boost only the queries that contribute to the tail latency; and second, per-query characteristics can be used to design indicators for proactively pinpointing these queries, triggering boosting accordingly. Based on these insights, Adrenaline effectively pinpoints and boosts queries that are likely to increase the tail distribution and can reap more benefit from the voltage/frequency boost. By evaluating under various workload configurations, we demonstrate the effectiveness of our methodology. We achieve up to a 2.50x tail latency improvement for Memcached and up to a 3.03x for Web Search over coarse-grained DVFS given a fixed boosting power budget. When optimizing for energy reduction, Adrenaline achieves up to a 1.81x improvement for Memcached and up to a 1.99x for Web Search over coarse-grained DVFS. I.