Receive Side Coalescing for Accelerating TCP/IP Processing

With rapid advancements in Ethernet technology, Ethernet speeds have increased by 10 fold, from 1 to 10Gbps, in a period of 2-3 years. This sudden increase in speeds has outpaced the rate at which processor and memory speeds have been increasing, raising concerns that TCP/IP processing will not scale to these levels. As a result, applications running on commercial servers will not be able to take advantage of the increased Ethernet bandwidth. This has led to a flurry of activity in the industry and academia focused on finding ways to scale up TCP/IP processing to 10Gbps and beyond. In this paper, we propose a novel technique called "Receive Side Coalescing" (RSC) that increases TCP/IP processing efficiencies significantly. RSC allows NICs to identify packets that belong to same TCP/IP flow and coalesce them into a single large packet. As a result, TCP/IP stack has to process fewer packets reducing per packet processing costs. NIC can do this coalescing of packets during interrupt moderation time, hence packet latency is not effected. We have collected packet traces and analyzed those to find out how much coalescing is possible in different scenarios. Our analysis shows that about 50% reduction in number of packets is possible. We have prototyped RSC on Windows and Linux to understand the benefits, and the results show that 2-7% of savings in CPU utilization is possible at 1Gbps speeds. Projection models developed to estimate processing costs at 10Gbps show that RSC can save up to 20% of the CPU.