Abstract-Due to the growing need to tolerate network faults and congestion in high-end computing systems, supporting multiple network communication paths is becoming increasingly important. However, multi-path communication comes with the disadvantage of out-oforder arrival of packets (because packets may traverse different paths). While modern networking stacks such as the Internet Wide-Area RDMA Protocol (iWARP) over 10-Gigabit Ethernet (10GE) support multi-path communication, their current implementations do not handle out-of-order packets primarily owing to the overhead on in-order communication that it adds. Specifically, in iWARP, supporting out-of-order packets requires every packet to carry additional information causing significant overhead on packets that arrive in-order. Thus, in this paper, we analyze the trade-offs in designing a featurecomplete iWARP stack, i.e., one that provides support for out-of-order arriving packets, and thus, multi-path systems, while focusing on the performance of in-order communication. We propose three feature-complete designs of iWARP and analyze the pros and cons of each of these designs using performance experiments based on several micro-benchmarks as well as an iso-surface visual rendering application. Our analysis reveals that the iWARP design providing the best overall performance depends on the particular characteristics of the upper layers and that different designs are optimal based on the metric of interest.
The Sockets Direct Protocol (SDP) is an industry standard to allow existing TCP/IP applications to be executed on high-speed networks such as InfiniBand (IB). Like many other high-speed networks, IB requires the receiver process to inform the network interface card (NIC), before the data arrives, about buffers in which incoming data has to be placed. To ensure that the receiver process is ready to receive data, the sender process typically performs flow-control on the data transmission. Existing designs of SDP flow-control are naive and do not take advantage of several interesting features provided by IB. Specifically, features such as RDMA are only used for performing zero-copy communication, although RDMA has more capabilities such as sender-side buffer management (where a sender process can manage SDP resources for the sender as well as the receiver). Similarly, IB also provides hardware flow-control capabilities that have not been studied in previous literature. In this paper, we utilize these capabilities to improve the SDP flow-control over IB using two designs: RDMA-based flow-control and NIC-assisted RDMA-based flow-control. We evaluate the designs using micro-benchmarks and real applications. Our evaluations reveal that these designs can improve the resource usage of SDP and consequently its performance by an order-of-magnitude in some cases. Moreover we can achieve 10-20% improvement in performance for various applications.
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