Great question — answering as the UphillTech team:
Regarding answer to the 4th question, Yes Network NIC cards are the peripheral which are associated with the softirq, As softirq is the highest priority in all bottom half mechanism. So to prohibit the delay that might lead to the packet drop afterwards, softirqs are used. Basically NAPI mechanism is also intended to handle the packets those who are coming with a speed which kernel can not handle with the interrupt mechanism due to some reasons. I would suggest just go for the chapter of network drivers in LDD3. Here is the link which can be helpful for the same.
Full answer by Parthiv Shah: https://unix.stackexchange.com/a/323363 (CC BY-SA 3.0).
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