Once upon a time, everything was so simple. The network card was slow and had only one queue. When packets arrives, the network card copies packets through DMA and sends an interrupt, and the Linux kernel harvests those packets and completes interrupt processing. As the network cards became faster, the interrupt based model may cause IRQ storm due to the massive incoming packets. This will consume the most of CPU power and freeze the system. To solve this problem, NAPI (interrupt + polling) was proposed. When the kernel receives an interrupt from the network card, it starts to poll the device and harvest packets in the queue as fast as possible. NAPI works nicely with the 1 Gbps network card which is common nowadays. However, it comes to the 10 Gbps, 20 Gbps, or even 40 Gbps network cards, NAPI may not be sufficient. Those cards would demand much faster CPU if we still use one CPU and one queue to receive packets. Fortunately, multi-core CPUs are popular now, so why not process pa...