TechTalks from event: IEEE IPDPS 2011

Note 1: Only plenary sessions (keynotes, panels, and best papers) are accessible without requiring log-in. For other talks, you will need to log-in using the email you registered for IPDPS 2011. Note 2: Many of the talks (those without a thumbnail next to the their description below) are yet to be uploaded. Some of them were not recorded because of technical problems. We are working with the corresponding authors to upload the self-recorded versions here. We sincerely thank all authors for their efforts in making their videos available.

SESSION 11: Multiprocessing and Concurrency

  • Hardware-based Job Queue Management for Manycore Architectures and OpenMP Environments Authors: Junghee Lee (Georgia Institute of Technology, USA); Chrysostomos Nicopoulos (University of Cyprus, Cyprus); Yongjae Lee (Georgi
    The seemingly interminable dwindle of technology feature sizes well into the nano-scale regime has afforded computer architects with an abundance of computational resources on a single chip. The Chip Multi-Processor (CMP) paradigm is now seen as the de facto architecture for years to come. However, in order to ef?ciently exploit the increasing number of on-chip processing cores, it is imperative to achieve and maintain ef?cient utilization of the resources at run time. Uneven and skewed distribution of workloads misuses the CMP resources and may even lead to such undesired effects as traf?c and temperature hotspots. While existing techniques rely mostly on software for the undertaking of load balancing duties and exploit hardware mainly for synchronization, we will demonstrate that there are wider opportunities for hardware support of load balancing in CMP systems. Based on this fact, this paper proposes IsoNet, a con?ict-free dynamic load distribution engine that exploits hardware aggressively to reinforce massively parallel computation in manycore settings. Moreover, the proposed architecture provides extensive fault-tolerance against both CPU faults and intra-IsoNet faults. The hardware takes charge of both (1) the management of the list of jobs to be executed, and (2) the transfer of jobs between processing elements to maintain load balance. Experimental results show that, unlike the existing popular techniques of blocking and job stealing, IsoNet is scalable with as many as 1024 processing cores.
  • HK-NUCA: Boosting Data Searches in Dynamic Non-Uniform Cache Architectures for Chip Multiprocessors Authors: Javier Lira (Universitat Politècnica de Catalunya, Spain); Carlos Molina (Universitat Rovira i Virgili, Spain); Antonio
    The exponential increase in the cache sizes of multicore processors (CMPs) accompanied by growing on-chip wire delays make it dif?cult to implement traditional caches with single and uniform access latencies. Non-Uniform Cache Architecture (NUCA) designs have been proposed to address this problem. NUCA divides the whole cache memory into smaller banks and allows nearer cache banks to have lower access latencies than farther banks, thus mitigating the effects of the cache’s internal wires. Traditionally, NUCA organizations have been classi?ed as static (S-NUCA) and dynamic (D-NUCA). While in S-NUCA a data block is mapped to a unique bank in the NUCA cache, D-NUCA allows a data block to be mapped in multiple banks. Besides, D-NUCA designs are dynamic in the sense that data blocks may migrate towards the cores that access them most frequently. Recent works consider D-NUCA as a promising design, however, in order to obtain signi?cant performance bene?ts, they used a non-affordable access scheme mechanism to ?nd data in the NUCA cache. In this paper, we propose a novel and implementable data search algorithm for D-NUCA designs in CMP architectures, which is called HK-NUCA (Home Knows where to ?nd data within the NUCA cache). It exploits migration features by providing fast and power ef?cient accesses to data which is located close to the requesting core. Moreover, HK-NUCA implements an ef?cient and cost-effective search mechanism to reduce miss latency and on-chip network contention. We show that using HK-NUCA as data search mechanism in a D-NUCA design reduces about 40% energy consumed per each memory request, and achieves an average performance improvement of 6%.
  • Power Token Balancing: Adapting CMPs to Power Constraints for Parallel Multithreaded Workloads Authors: Juan M. Cebrián (University of Murcia, Spain); Juan L. Aragón (University of Murcia, Spain); Stefanos Kaxiras (Un
    In the recent years virtually all processor architectures employ multiple cores per chip (CMPs). It is possible to use legacy (i.e., single-core) power saving techniques in CMPs which run either sequential applications or independent multithreaded workloads. However, new challenges arise when running parallel shared-memory applications. In the later case, sacri?cing some performance in a single core (thread) in order to be more energy-ef?cient might unintentionally delay the rest of cores (threads) due to synchronization points (locks/barriers), therefore, harming the performance of the whole application. CMPs increasingly face thermal and power-related problems during their typical use. Such problems can be solved by setting a power budget to the processor/core. This paper initially studies the behavior of different techniques to match a prede?ned power budget in a CMP processor. While legacy techniques properly work for thread independent/multi-programmed workloads, parallel workloads exhibit the problem of independently adapting the power of each core in a thread dependent scenario. In order to solve this problem we propose a novel mechanism, Power Token Balancing (PTB), aimed at accurately matching an external power constraint by balancing the power consumed among the different cores using a power tokenbased approach while optimizing the energy ef?ciency. We can use power (seen as tokens or coupons) from non-critical threads for the bene?t of critical threads. PTB runs transparent for thread independent / multiprogrammed workloads and can be also used as a spinlock detector based on power patterns. Results show that PTB matches more accurately a prede?ned power budget (total energy consumed over the budget is reduced to 8% for a 16-core CMP) than DVFS with only a 3% energy increase. Finally, we can trade accuracy on matching the power budget for energy-ef?ciency reducing the energy a 4% with a 20% of accuracy.
  • A Very Fast Simulator For Exploring The Many-Core Future Authors: Olivier Certner (INRIA, France); Zheng Li (INRIA, France); Arun Raman (Princeton University, USA); Olivier Temam (INRIA Futurs,
    Although multi-core architectures with a large number of cores (“many-cores”) are considered the future of computing systems, there are currently few practical tools to quickly explore both their design and general program scalability. In this paper, we present SiMany, a discrete-event-based many-core simulator able to support more than a thousand cores while being orders of magnitude faster than existing ?exible approaches. One of the dif?cult challenges for a reasonably realistic many-core simulation is to model faithfully the potentially high concurrency a program can exhibit. SiMany uses a novel virtual time synchronization technique, called spatial synchronization, to achieve this goal in a completely local and distributed fashion, which diminishes interactions and preserves locality. Compared to previous simulators, it raises the level of abstraction by focusing on modeling concurrent interactions between cores, which enables fast coarse comparisons of high-level architecture design choices and parallel programs performance. Sequential pieces of code are executed natively for maximal speed. We exercise the simulator with a set of dwarf-like task-based benchmarks with dynamic control ?ow and irregular data structures. Scalability results are validated through comparison with a cycle-level simulator up to 64 cores. They are also shown consistent with well-known benchmark characteristics. We ?nally demonstrate how SiMany can be used to ef?ciently compare the benchmarks’ behavior over a wide range of architectural organizations, such as polymorphic architectures and network of clusters