Hip

The standard way to notify the processor of a network event, such as the arrival or transmission of a packet, is through interrupts. Interrupts are more effective than polling, in terms of the per packet send/receive latency. Interrupts, however, incur a high overhead both during and after the interrupt handling, because modern superscalar processors use long pipelines, out-of-order and speculative execution, and multi-level memory systems, all of which tend to increase the interrupt overhead in terms of clock cycles. In this paper, we attempt to reduce the network interface overhead by introducing a hybrid scheme (HIP) that uses interrupts under low network load conditions and polling otherwise. Even though such hybrid schemes have been proposed in the past, the polling period in HIP is adjusted dynamically based on the rate of the arriving packet stream. In this way, the increase in the per packet latency, which occurs with polling, is quite low. This is quantified with trace-driven simulations, which also show that the per packet overhead with HIP is significantly reduced compared to the conventional interrupt-based mechanism. HIP would be beneficial for high bandwidth network interfacing in servers with a heavy WWW or streaming media workload.