Power is the most critical resource for the exascale high performance computing. In the future, system administrators might have to pay attention to the power consumption of the machine under different work loads. Hence, each application may have to run with an allocated power budget. Thus, achieving the best performance on future machines requires optimal performance subject to a power constraint. This additional performance requirement should not be the responsibility of HPC~(High Performance Computing) application developers. Optimizing the performance for a given power budget should be the responsibility of high-performance system software stack. Modern machines allow power capping of CPU and memory to implement power budgeting strategy. Finding the best runtime environment for a node at a given power level is important to get the best performance. This paper presents ARCS (Adaptive Runtime Configuration Selection) frameworkthat automatically selects the best runtime configuration for each OpenMPparallel region at a given power level. The framework uses OMPT (OpenMP Tools) API, APEX(Autonomic Performance Environment for eXascale), and Active Harmony frameworksto explore configuration search space and selects the best number of threads, scheduling policy, and chunk size for a given power level at run-time. We test ARCS using the NAS Parallel Benchmark, and proxy application LULESH with Intel Sandybridge, and IBM Power multi-core architectures. We show that for a given power level, efficient OpenMP runtime parameter selection can improve the execution time and energy consumption of an application up to 40% and 42% respectively.

Malleable jobs are those which can dynamically shrink or expand the number of processors on which they are executing at runtime in response to an external command. Malleable jobs can significantly improve system utilization and reduce average response time, compared to traditional jobs. To realize these benefits, three components are critical - an adaptive job scheduler, an adaptive resource manager, and an adaptive parallel runtime system. In this paper, we present a novel mechanism for enabling shrink/expand capability in the parallel runtime system using task migration and dynamic load balancing, checkpoint-restart, and Linux shared memory. Our technique performs true shrink/expand eliminating the need of any residual processes, requires little application programmer effort, and is fast. Further, we establish a bidirectional communication channel between the resource manager and the parallel runtime, and present an asynchronous split-phase mechanism for executing adaptive scheduling decisions. Performance results using Charm++ on Stampede supercomputer show the efficacy, scalability, and benefits of our approach. Shrinking from 2k to 1k cores takes 16s while expand from 1k to 2k takes 40s. Also, we demonstrate the utility of our runtime in traditional as well as emerging scenarios, e.g., proactive fault tolerance and clouds.

Building future generation supercomputers while constraining their power consumption is one of the biggest challenges faced by the HPC community. For example, US Department of Energy has set a goal of 20 MW for an exascale (1018 flops) supercomputer. To realize this goal, a lot of research is being done to revolutionize hardware design to build power efficient computers and network interconnects. In this work, we propose a software-based online resource management system that leverages hardware facilitated capability to constrain the power consumption of each node in order to optimally allocate power and nodes to a job. Our scheme uses this hardware capability in conjunction with an adaptive runtime system that can dynamically change the resource configuration of a running job allowing our resource manager to re-optimize allocation decisions to running jobs as new jobs arrive, or a running job terminates. We also propose a performance modeling scheme that estimates the essential power characteristics of a job at any scale. The proposed online resource manager uses these performance characteristics for making scheduling and resource allocation decisions that maximize the job throughput of the supercomputer under a given power budget. We demonstrate the benefits of our approach by using a mix of jobs with different power response characteristics. We show that with a power budget of 4:75 MW, we can obtain up to 5:2X improvement in job throughput when compared with the SLURM scheduling policy that is power-unaware. We corroborate our results with real experiments on a relatively small scale cluster, in which we obtain a 1:7X improvement.

Driven by the benefits of elasticity and pay-as-you-go model, cloud computing is emerging as an attractive alternative and addition to in-house clusters and supercomputers for some High Performance Computing (HPC) applications. However, poor interconnect performance, heterogeneous and dynamic environment, and interference by other virtual machines (VMs) are some bottlenecks for efficient HPC in cloud. For tightly-coupled iterative applications, one slow processor slows down the entire application, resulting in poor CPU utilization. In this paper, we present a dynamic load balancer for tightly-coupled iterative HPC applications in cloud. It infers the static hardware heterogeneity in virtualized environments, and also adapts to the dynamic heterogeneity caused by the interference arising due to multi-tenancy. Through continuous live monitoring, instrumentation, and periodic refinement of task distribution to VMs, our load balancer adapts to the dynamic variations in cloud resources. Through experimental evaluation on a private cloud with 64 VMs using benchmarks and a real science application, we demonstrate performance benefits up to 45%. Finally, we analyze the effect of load balancing frequency, problem size, and computational granularity (problem decomposition) on the performance and scalability of our techniques.

As we move towards the exascale era, power and energy have become major challenges. Some of the supercomputers draw more than 10 megawatts, leading to high energy bills. A significant portion of this energy is spent in cooling. In this paper, we propose an adaptive control system that minimizes the cooling energy by using Dynamic Voltage and Frequency Scaling to control the temperature and performing load balancing. This framework, which is a part of the adaptive runtime system, monitors the system and application characteristics and triggers mechanism to limit the temperature. It also performs load balancing whenever imbalance is detected and load balancing is beneficial. We demonstrate, using a set of applications and benchmarks, that the proposed framework can control the temperature of the cores effectively and reduce the timing penalty automatically without any support from the user.

Energy consumption and power draw pose two major challenges to the HPC community for designing larger systems. Present day HPC systems consume as much as 10MW of electricity and this is fast becoming a bottleneck. Although energy bills will significantly increase with machine size, power consumption is a hard constraint that must be addressed. Intel's Running Average Power Limit (RAPL) toolkit is a recent feature that enables power capping of CPU and memory subsystems on modern hardware. In this paper, we use RAPL to evaluate the possibility of improving execution time efficiency of an application by capping power while adding more nodes. We profile the strong scaling of an application using different power caps for both CPU and memory subsystems. Our proposed interpolation scheme uses an application profile to optimize the number of nodes and the distribution of power between CPU and memory subsystems to minimize execution time under a strict power budget. We validate these estimates by running experiments on a 20-node (120 cores) Sandy Bridge cluster. Our experimental results closely match the model estimates and show speedups greater than 1.47X for all applications compared to not capping CPU and memory power. We demonstrate that the quality of solution that our interpolation scheme provides matches very closely to results obtained via exhaustive profiling.

Soaring energy consumption, accompanied by declining reliability, together loom as the biggest hurdles for the next generation of supercomputers. Recent reports have expressed concern that reliability at exascale level could degrade to the point where failures become a norm rather than an exception. HPC researchers are focusing on improving existing fault tolerance protocols to address these concerns. Research on improving hardware reliability, i.e., machine component reliability, has also been making progress independently. In this paper, we try to bridge this gap and explore the potential of combining both software and hardware aspects towards improving reliability of HPC machines. Fault rates are known to double for every 10°C rise in core temperature. We leverage this notion to experimentally demonstrate the potential of restraining core temperatures and load balancing to achieve two-fold benefits: improving reliability of parallel machines and reducing total execution time required by applications. Our experimental results show that we can improve the reliability of a machine by a factor of 2.3 and reduce the execution time by 12%. In addition, our scheme can also reduce machine energy consumption by as much as 25%. For a 350K socket machine, regular checkpoint/restart fails to make progress (less than 1% efficiency), whereas our validated model predicts an efficiency of 20% by improving the machine reliability by a factor of up to 2.29.

An exascale machine is expected to be delivered in the time frame 2018-2020. Such a machine will be able to tackle some of the hardest computational problems and to extend our understanding of Nature and the universe. However, to make that a reality, the HPC community has to solve a few important challenges. Resilience will become a prominent problem because an exascale machine will experience frequent failures due to the large amount of components it will encompass. Some form of fault tolerance has to be incorporated in the system to maintain the progress rate of applications as high as possible. In parallel, the system will have to be more careful about power management. There are two dimensions of power. First, in a power-limited environment, all the layers of the system have to adhere to that limitation (including the fault tolerance layer). Second, power will be relevant due to energy consumption: an exascale installation will have to pay a large energy bill. It is fundamental to increase our understanding of the energy profile of different fault tolerance schemes. This paper presents an evaluation of three different fault tolerance approaches: checkpoint/restart, message-logging and parallel recovery. Using programs from different programming models, we show parallel recovery is the most energy-efficient solution for an execution with failures. At the same time, parallel recovery is able to finish the execution faster than the other approaches. We explore the behavior of these approaches at extreme scales using an analytical model. At large scale, parallel recovery is predicted to reduce the total execution time of an application by 17% and reduce the energy consumption by 13% when compared to checkpoint/restart.

Information Set Generation (ISG) is the identification of the set of paths in an imperfect information game tree that are consistent with a player's observations. The ability to reason about the possible a history is critical to the performance of game-playing agents. ISG represents a class of combinatorial search problems which is computationally intensive but challenging to efficiently parallelize. In this paper, we address the parallelization of information set generation in the context of Kriegspiel (partially observable chess). We implement the algorithm on top of a general purpose combinatorial search engine and discuss its performance using datasets from real game instances in addition to benchmarks. Further, we demonstrate the effect of load balancing strategies, problem sizes and computational granularity (grain size parameters) on performance. We achieve speedups of over 500 on 1,024 processors, far exceeding previous scalability results for game tree search applications.

As we move to exascale machines, both peak power demand and total energy consumption have become prominent challenges. A significant portion of that power and energy consumption is devoted to cooling, which we strive to minimize in this work. We propose a scheme based on a combination of limiting processor temperatures using dynamic voltage and frequency scaling (DVFS) and frequency-aware load balancing that reduces cooling energy consumption and prevents hot spot formation. Our approach is particularly designed for parallel applications, which are typically tightly coupled, and tries to minimize the timing penalty associated with temperature control. This paper describes results from experiments using five different Charm++ and MPI applications with a range of power and utilization profiles. They were run on a 32-node (128-core) cluster with a dedicated air conditioning unit. The scheme is assessed based on three metrics: the ability to control processors' temperature and hence avoid hot spots, minimization of timing penalty, and cooling energy savings. Our results show cooling energy savings of up to 63 percent, with a timing penalty of only 2-23 percent.

Meeting power requirements of huge exascale machines of the future will be a major challenge. Our focus in this paper is to minimize cooling power and we propose a technique that uses a combination of DVFS and temperature aware load balancing to constrain core temperatures as well as save cooling energy. Our scheme is specifically designed to suit parallel applications which are typically tightly coupled. The temperature control, comes at the cost of execution time and we try to minimize the timing penalty.