S.124-135

Multithreading has been promoted as an effective mechanism to hide inter-processor communications and remote data access latencies by quickly switching among a set of ready threads. In this paper, we show that multitreading provides an immunity to the performance variations due to changes in data distributions in a distributed-memory multiprocessor. First, toe propose two performance metrics to quantify the sensitivity of performance to data-locality. Second, we perform a quantitative comparison of data-locality sensitivity with both single-threaded and multithreaded computations. These experiments are performed on a 20-node EARTH-MANNA system. Our results show that not only does a multithreaded computation yields higher performance than the single-threaded version, but also that its performance is more robust (less affected) by variations in data-locality.

Parallel systems supporting multithreading, or message passing in general, have typically used either polling or interrupts to handle incoming messages. Neither approach is ideal; either may lead to excessive overheads or message-handling latencies, depending on the application. This paper investigates a combined approach---Polling Watchdog, where both are used depending on the circumstances. The Polling Watchdog is a simple hardware extension that limits the generation of interrupts to the cases where explicit polling fails to handle the message quickly. As an added benefit, this mechanism also has the potential to simplify the interaction between interrupts and the network accesses performed by the program.We present the resulting performance for the EARTH-MANNA-S system, an implementation of the EARTH (Efficient Architecture for Running THreads) execution model on the MANNA multiprocessor. In contrast to the original EARTH-MANNA system, this system does not use a dedicated communication processor. Rather, synchronization and communication tasks are performed on the same processor as the regular computations. Therefore, an efficient message-handling mechanism is essential to good performance. Simulation results and performance measurements show that the Polling Watchdog indeed performs better than either polling or interrupts alone. In fact, this mechanism allows the EARTH-MANNA-S system to achieve the same level of performance as the original EARTH-MANNA multithreaded system.