Protocol offload analysis by simulation

In the last years, diverse network interface designs have been proposed to cope with the link bandwidth increase that is shifting the communication bottleneck towards the nodes in the network. The main point behind some of these network interfaces is to reach an efficient distribution of the communication overheads among the different processing units of the node, thus leaving more host CPU cycles for the applications and other operating systems tasks. Among these proposals, protocol offloading searches for an efficient use of the processing elements in the network interface card (NIC) to free the host CPU from network processing. The lack of both, conclusive experimental results about the possible benefits and a deep understanding of the behavior of these alternatives in their different parameter spaces, have caused some controversy about the usefulness of this technique. The contributions of this paper deal with the implementation and evaluation of offloading strategies and with the need of accurate tools for researching the computer system issues that, as networking, require the analysis of interactions among applications, operating system, and hardware. Thus, in this paper, a way to include timing models in a full-system simulator (Simics) to provide a suitable tool for network subsystem simulation is proposed. Moreover, we compare two kinds of simulators, a hardware description language level simulator and a full-system simulator (including our proposed timing models), in the analysis of protocol offloading at different levels. We also explain the results obtained from the perspective of the previously described LAWS model and propose some changes in this model to get a more accurate approach to the experimental results. From these results, it is possible to conclude that offloading allows a relevant throughput improvement in some circumstances that can be qualitatively predicted by the LAWS model. 2008 Elsevier B.V. All rights reserved.