• Communication Structures (Tuesday 10:30AM-Noon)
    Room A108/110/112
    Chair: Phil Papadopoulos, NPACI

    • Title: ORT - A Communication Library for Orthogonal Processor Groups
    • Authors:
      Thomas Rauber (Institut für Informatik, Universität Halle-Wittenberg)
      Robert Reilein (Fakultät für Informatik, Technische Universität Chemnitz)
      Gudula Rünger (Fakultät f¸r Informatik, Technische Universität Chemnitz)
    • Abstract:
      Many implementations on message-passing machines can benefit from an exploitation of mixed task and data parallelism. A suitable parallel programming model is a group-SPMD model, which requires a structuring of the processors into subsets and a partition of the program into multi-processor tasks. In this paper, we introduce a library support for the specification of message-passing programs in a group-SPMD style allowing different partitions in a single program. We describe the functionality and the implementation of the library functions and illustrate the library programming style with example programs. The examples show that the runtime on distributed memory machines can be considerably reduced by using the library.

    • Title: On-the-fly Calculation and Verification of Consistent Steering Transactions
    • Authors:
      David W. Miller (University of Georgia)
      Jinhua Guo (University of Georgia)
      Eileen Kraemer (University of Georgia)
      Yin Xiong (University of Georgia)
    • Abstract:
      Interactive Steering can be a valuable tool for understanding and controlling a distributed computation in real-time. With Interactive Steering, the user may change the state of a computation by adjusting application parameters on-the-fly. In our system, we model both the programís execution and steering actions in terms of transactions. We define a steering transaction as consistent if its vector time is not concurrent with the vector time of any program transaction. That is, consistent steering transactions occur ìbetweenî program transactions, at a point that represents a consistent cut. In this paper, we present an algorithm for verifying the consistency of steering transactions. The algorithm analyzes a record of the program transactions and compares it against the steering transaction; if the time at which the steering transaction was applied is inconsistent, the algorithm generates a vector representing the earliest consistent time at which the steering transaction could have been applied.

    • Title: Removing the Overhead from Software-Based Shared Memory
    • Authors:
      Zoran Radovic (Uppsala University)
      Erik Hagersten (Uppsala University)
    • Abstract:
      The implementation presented in this paper---DSZOOM-WF---is a sequentially consistent, fine-grained distributed software-based shared memory. It demonstrates a protocol-handling overhead below a microsecond for all the actions involved in a remote load operation, to be compared to the fastest implementation to date of around ten microseconds.

      The all-software protocol is implemented assuming some basic low-level primitives in the cluster interconnect and an operating system bypass functionality, similar to the emerging InfiniBand standard. All interrupt-and/or poll-based asynchronous protocol processing is completely removed by running the entire coherence protocol in the requesting processor. This not only removes the asynchronous overhead, but also makes use of a processor that otherwise would stall. The technique is applicable to both page-based and fine-grain software-based shared memory.

      DSZOOM-WF consistently demonstrates performance comparable to hardware-based distributed shared memory implementations.