Congestion Control for Asynchronous Parallel Computing on Workstation Networks

Asynchronous parallel computing can result in high message generation rates, thus triggering network congestion. This paper investigates the network congestion problem that can result from asynchronous parallel programs' high message generation rates. First, we characterize the communication requirements of a large class of supercomputing applications falling under the category of xed-point problems amenable to solution by parallel iterative methods. In particular , we concentrate on asynchronous iterative algorithms whose communication/computation ratio is especially high resulting in degraded eeective throughput if communication is not managed properly. Second, we show the eeects of network contention and asynchrony on application performance in a local-area network environment and investigate methods of solution. Our approach is based on a congestion control algorithm called Warp Control whose adaptive properties are exploited to yield signiicant performance enhancements when network contention is high. Although tested in a LAN environment for experimental control purposes, our solution follows the end-to-end paradigm and refrains from exploiting special MAC-layer properties to achieve applicability to general WAN environments. Third, we provide a framework wherein eecient congestion control can be facilitated, encompassing methods acting at the application layer as well as the transport/network layer, with emphasis on application-driven control. We conclude with a discussion of our experimental results and special issues arising in high-bandwidth ATM networks.