As known there are two approach to avoid some overheads of hardware interrupts in highload networks, when there are too many hardware interrupts, that switching to them takes too much time. It is very important for performance and choosing approach of programm style. NAPI vs Adaptive Interrupts
- NAPI (New API) - Does not use hardware interrupts, and polls the Ethernet-device every certain period of time. The Linux kernel uses the interrupt-driven mode by default and only switches to polling mode when the flow of incoming packets exceeds a certain threshold.
http://en.wikipedia.org/wiki/New_API The kernel can periodically check for the arrival of incoming network packets without being interrupted, which eliminates the overhead of interrupt processing.
- Interrupt coalescing - Uses hardware interrupts, but if interrupt occur, then disables interrupt and starts poll, for certain period of time, after which the polling is terminated and the interrupt is activated.
https://en.wikipedia.org/wiki/Interrupt_coalescing a technique in which events which would normally trigger a hardware interrupt are held back, either until a certain amount of work is pending, or a timeout timer triggers.
Both approaches have not significant costs of interruption - this is advantage befor default interrupt-driven mode.
But the second approach - Interrupt coalescing is more rational because it:
Less latency - Once the package arrived, immediately tries to handle it immediately interrupt occurs or poll it if the interrupt has occurred recently. Opposite NAPI will not process the frame immediately, but will wait certain period of time for the next poll.
Less CPU usage - Starts the poll only if at least one packet has already come. But is not doing a poll in vain, even if frames has not received, as if it did NAPI.
What are the advantages NAPI before the IRQ Coalesce?
