Estimating the Impact of Interrupt Coalescing Delays on Steady State TCP Throughput

Interrupt coalescing is a feature implemented in hardware on many of today’s high-performance network interface cards (NIC). It allows a reception of a group of network frames to be notified to the operating system kernel via a single hardware interrupt, thus reducing the interrupt processing overhead, particularly at high packet rates. However, the delays introduced by interrupt coalescing can result in significant TCP throughput degradation. In this article we analyze the advantages and drawbacks of a generic interrupt coalescing implementation. We propose an approximate model defining relation between interrupt coalescing delays and steady state TCP throughput, which we validate by laboratory measurements. We conclude our report by showing how the proposed model can be used for determination of optimal delay duration, depending on specific environment and application.